Grade 4 Science — every video script

Here's Elena on a winter morning, with her sled on the grass by the park gate.

She pulls hard, but the sled hardly moves.

Then she reaches the snow. The same sled glides on and on, and she has to run to keep up.

The sled is the same, and Elena is the same. So what is different about the snow and the grass?

To find out, we will see what happens where a sled rubs the ground, why moving things stop, and which surfaces let things slide farther.

Okay, so are you ready to find out why sliding things stop?

Here's Elena in her classroom. She pushes a box full of books across the floor, and it is hard work.

When she stops pushing, the box slides a little and stops. Nobody pulls it back, so what works against her push?

Here, the bottom of the box rubs against the floor. Right there, a force pushes against the sliding. That force is called friction.

And now Elena rubs an eraser across her desk. The eraser rubs against the desk, so friction pushes against the sliding.

But now Elena throws the eraser across the room. The eraser touches no surface as it flies. No rubbing force acts on it. There is no friction.

So, every time two surfaces rub, friction pushes against the sliding. The force that acts when two surfaces rub is called friction.

Okay, now your turn.

Here's Carmen in her bedroom. She wants her bed by the window, so she pushes it. She pushes hard, but the bed does not move.

Nobody is pushing the bed the other way, so what stops her push from moving it?

Carmen pushes the bed one way. The bed stays still, so something must push it back the other way.

Where the bed's legs press on the floor, friction pushes back against her push. Her push and friction are balanced, so the bed stays still.

Friction acts as soon as she tries to slide the bed, even before it moves.

And now Carmen pushes harder. The bed starts to slide, and friction still pushes back against her push, so it is hard work.

So, friction always acts against the direction you are trying to push something.

Okay, now your turn.

Here's Darnell on the sidewalk. He gives a wooden block a push and lets go.

The block slides, slows down, and stops. Nobody touched it, so why did it stop?

A moving thing does not stop by itself. Where the block rubs against the sidewalk, friction pushes against the sliding, until the block stops.

Some people say the push ran out. But a push is not inside the block. Darnell's push acted only while his hand touched it. After that, friction stopped the block.

And now Darnell slides the same block along the smooth hall floor. Only a little friction pushes against it here, and nobody pushes the block, yet it slides on and on, much farther than on the sidewalk.

So, a sliding thing slows down and stops because friction pushes against it.

Okay, now your turn.

Here's Elena at home with a book. She gives it the same gentle push on the wooden floor, then on the carpet.

On the wood, the book slides to the far wall. On the carpet it stops after about 1 meter. The push was the same, so why does it go farther on the wood?

Look closely at the carpet. It is rough, so the book rubs against it hard. Friction is greater between the book and the carpet, so it stops sooner.

Now look at the wood. It is smooth, so the book rubs against it a little. Friction is less between the book and the wood, so the same push takes it farther.

More friction means a stronger push against the sliding.

Here's the pattern. Friction is less between a smoother surface and the thing sliding on it, so the same thing slides farther.

Okay, now your turn.

Here's Reed on an icy path. His foot slides out from under him. On the dry path, his shoe grips.

Friction acts where Reed's shoe presses on the path, so it does not slip. He wants the grip, so friction is helpful.

And now consider a bike brake. Its pads rub against the wheel, so friction slows the bike. The rider wants to slow down, so friction is helpful.

But now consider a door that sticks in its frame. Friction between the door and the frame makes it hard to open. You want it to swing, so friction is unhelpful.

A stuck kitchen drawer is the same. Friction between the drawer and the cabinet pushes against the sliding. You want it to slide, so friction is unhelpful.

So, friction is helpful when you want the grip or the slowing, and unhelpful when you want the sliding.

Okay, now your turn.

Here's everything we found out about why sliding things stop.

First, the force that acts when two surfaces rub is called friction.

Next, friction always acts against the direction you are trying to push something. It pushes back even before the thing moves.

Then, a moving thing does not stop by itself. A sliding thing slows down and stops because friction pushes against it.

After that, friction is less between a smoother surface and the thing sliding on it, so the same thing slides farther. More friction means a stronger push against the sliding.

And last, friction is helpful when you want the grip or the slowing, and unhelpful when you want the sliding.

Okay, now your turn.

Here's Miss Alvarez's class in the school hallway, and Maeve has a toy car and a small ramp.

She lets the car go on the tile, and it rolls a long way.

Then she moves the ramp onto the carpet, and this time the car stops after a short way.

Felipe says that proves it: the tile lets the car go farthest. But Niall is not so sure.

So how does the class find out for sure, in a way nobody can argue with?

To find out, we will look at what you change, what you keep the same, and what you measure.

Okay, so are you ready to run a test everyone can trust?

Here's Miss Alvarez's class in the hallway with a toy car and a small ramp. The class wants to find out about the floors.

Felipe writes: which floor is the best? Niall writes: which floor lets our toy car slide farthest?

Which question can the class answer by trying it out?

Niall's question names something the class can do: slide the car on each floor, and measure how far it goes. So the class can try it out.

'Best' is an opinion: it is what one person thinks. Felipe picks the tile, and Maeve picks the carpet.

Nobody can measure an opinion, so the class cannot try out Felipe's question.

What you see or measure when you try something out is called an observation.

So, a question you can answer by trying something out and watching or measuring what happens is a question you can test.

Okay, now your turn.

Miss Alvarez's class is testing which floor lets the same toy car slide farthest. Maeve lets the car go from the top of a small ramp onto the tile floor.

Then the class carries the ramp to the wooden floor, and Maeve lets the car go again.

Then the class carries the ramp to the carpet, and Maeve lets the car go once more.

What is the one thing the class changes from one run to the next?

The floor changes: tile, then wood, then carpet. The class changes the floor on purpose, because the floor is what the question asks about.

So, in a test, the one thing you change on purpose is the thing your question asks about.

Okay, now your turn.

Miss Alvarez's class is testing which floor lets the same toy car slide farthest. On the tile, Maeve lets the car go from the ramp, and nobody touches it.

On the carpet, Felipe gives the car a push as it leaves the ramp, and the car goes farther than it did on the tile.

Niall says the carpet must be the floor that lets the car slide farthest. Why can the class not trust this result?

Two things changed between the tile run and the carpet run: the floor, and the push. So nobody can tell which one made the car go farther.

So, everything except the one thing you change must stay the same: the same car, the same ramp, the same start line, and no push.

Okay, now your turn.

Miss Alvarez's class has let the same toy car go from the ramp onto each floor, with no push. Now the class needs to say which floor let the car slide farthest.

Maeve wants to time how long the car keeps moving. Niall wants to measure how far the car slid, from the foot of the ramp to where it stopped.

Which measurement answers the class's question?

The question asks how far the car slides. So the class measures the distance it slid, in centimeters, with a tape measure, and on the tile the car slid 180 centimeters.

So, what you measure to see the result is the thing your question asks about, after the change.

Okay, now your turn.

Miss Alvarez's class also tests two bean plants, to see whether more water makes a plant grow taller. Felipe gives one plant more water and puts it on the sunny windowsill.

The other plant gets less water and sits in the dark corner. The plant on the windowsill grows taller.

Can the class say that the water made the difference?

No. Two things changed: the water and the light, so nobody can tell which one made the plant grow taller.

Now consider a class that dips two kinds of paper towel in the same amount of water, for the same time. Only the kind of towel changed, so the class can trust its result.

A test where only one thing is changed, and everything else stays the same, is called a fair test. This test changed two things, so it is not a fair test.

Okay, now your turn.

Miss Alvarez's class is ready to find out which floor lets the same toy car slide farthest. Before the class starts, Niall writes the plan on the board.

The question: which floor lets the same toy car slide farthest? We change: the floor, tile, wood or carpet.

We keep the same: the same car, the same ramp, the same start line, and no push. We measure: how far the car slides, in centimeters, with a tape measure.

Now the class runs the test. The car slides 180 centimeters on the tile, 150 centimeters on the wood, and 40 centimeters on the carpet.

So the tile lets the car slide farthest. To plan a fair test, write down the question, the one thing you change, what stays the same, and what you measure.

Okay, now your turn.

Here's everything we found out about how to run a fair test.

First, a question you can answer by trying something out and watching or measuring what happens is a question you can test.

Next, in a test, the one thing you change on purpose is the thing your question asks about.

And everything except the one thing you change must stay the same.

Then, what you measure to see the result is the thing your question asks about, after the change.

A test where only one thing is changed, and everything else stays the same, is called a fair test.

So, to plan a fair test, write down the question, the one thing you change, what stays the same, and what you measure.

Okay, now your turn.

A steel paperclip lies on Teddy's desk in Miss Okafor's class, and nobody is touching it.

Then the paperclip slides across the desk by itself.

Under the desk, Miss Okafor is sliding a magnet.

But when the magnet passes under Teddy's eraser, the eraser does not move at all.

And when Thea brings her own magnet close, Miss Okafor's magnet pushes Thea's magnet away.

So how does a magnet choose what to pull, and when does it push instead?

To find out, we will look at what a magnet pulls, the two ends of a magnet, and how close a magnet has to be.

Okay, so are you ready to find out how magnets push and pull?

Here's Thea's tray: a steel paperclip, a copper penny, an aluminum can tab, a brass key and a plastic button. She holds a magnet above it.

The paperclip jumps up to the magnet. Everything else stays, even the shiny metals.

The paperclip is steel, and a magnet pulls steel.

But the penny is copper. The magnet does not pull copper.

And the can tab is aluminum. The magnet does not pull aluminum.

Now Harvey adds an iron nail. It jumps up, so a magnet pulls iron.

And the brass key stays. A magnet does not pull brass.

A magnet also pulls two other metals: a shiny, silvery metal called nickel, and a silvery-gray metal called cobalt.

So, here's what we've seen. A magnet pulls steel and iron, without touching them. A magnet does not pull copper, aluminum or brass, even though they are metals.

Okay, now your turn.

Here's Harvey, holding a thread. A bar magnet hangs from the thread, so it can turn. Leia brings one end of her magnet close to it.

The hanging magnet swings toward Leia's magnet.

Now Leia turns her magnet around and brings the other end close. This time the hanging magnet swings away.

So the two ends of a magnet are different, even though they look the same.

Each end of a magnet is called a pole. Every magnet has two poles.

One pole is called the north pole, and the other is called the south pole. Bar magnets are often marked N and S.

So, a magnet has two different ends, called poles: a north pole and a south pole.

Okay, now your turn.

Here are two bar magnets on Leia's desk, with a north pole facing a north pole. Leia lets go.

The magnets slide apart, and nobody is touching them.

Now Leia turns one magnet around, so a north pole faces a south pole. She lets go, and the magnets slide together and stick.

Which poles face each other decides it. When a north pole faces a south pole, the magnets pull together.

When a north pole faces a north pole, the magnets push apart. And when a south pole faces a south pole, they push apart too.

When two magnets pull together, we say they attract. When two magnets push apart, we say they repel.

So, two different poles attract: they pull together. Two of the same pole repel: they push apart.

Okay, now your turn.

Here's Teddy at his desk, holding a magnet above a steel paperclip. The magnet is 10 centimeters above the paperclip, and nothing happens.

The magnet pulls the paperclip, but the pull is weak.

Now Teddy lowers the magnet to 5 centimeters. The pull is stronger, but the paperclip still stays.

Now he lowers it to 2 centimeters. The pull is strongest here, and the paperclip jumps up.

The paperclip jumps when the magnet's pull is stronger than Earth's pull on it.

So, here's what we've seen. The closer a magnet is to a thing, the stronger its pull on it.

Okay, now your turn.

Here's Thea's desk: a ruler across two book stacks, with cardboard hanging from it.

Under the cardboard, a steel paperclip hangs on a thread, touching nothing.

It seems impossible. It seems like a magic trick.

The paperclip is hovering in thin air. So how did she do it?

Thea lifts the cardboard away. A magnet is taped under the ruler.

The magnet pulls the paperclip up through the cardboard.

The pull of the magnet is balanced out by the pull of the Earth and the pull of the thread, so the paperclip hangs still.

Here's how Thea built it. First, a ruler across the books, a magnet taped under it.

Next, she taped a thread to the desk under the magnet, tied on the paperclip, lifted it up and let go.

So, a magnet's pull works without touching, and it works through cardboard and air.

Okay, now your turn.

Here's everything we found out about how magnets push and pull.

First, a magnet pulls steel and iron, without touching them. A magnet does not pull copper, aluminum or brass, even though they are metals. A magnet also pulls two other metals, nickel and cobalt.

Next, a magnet has two different ends, called poles: a north pole and a south pole.

Then, two different poles attract: they pull together. Two of the same pole repel: they push apart.

And the closer a magnet is to a thing, the stronger its pull on it.

Last, a magnet's pull works without touching, and it works through cardboard and air. That is what the floating paperclip shows.

Okay, now your turn.

Here's a school field on a sunny morning, and Miss Murphy's class is reading outside.

The Sun warms Bennett's face. Across the field, a band practices, and the drum booms. Bennett hears every beat.

The drum is far away, and the Sun is farther still. Nothing touched Bennett.

But his face warmed up, and the boom reached his ear. So what reached him, and how did it get across the whole field?

To find out, we will look at where energy comes from and where it goes, what carries it, and whether two things have to touch.

Okay, so are you ready to follow the energy across the field?

Here's Miss Murphy's class, reading outside on the sunny school field. A band practices far away.

The Sun warms Bennett's face, the drum booms in his ears, and inside, a lamp lights Blake's page.

Miss Murphy says the same thing happened three times.

The Sun's light carries energy to Bennett's face. The Sun is the giver, and his face is the receiver.

And now the drum's sound carries energy to Bennett's ear. The drum is the giver, and his ear is the receiver.

And now the lamp's light carries energy to the page. The lamp is the giver, and the page is the receiver.

But now Blake switches the lamp off, and its light does not carry energy to the page.

So, here's the pattern. When energy moves, the thing it comes from is the giver, and the thing it goes to is the receiver.

Okay, now your turn.

Here's Miss Murphy's class on a cold day. She plugs in the electric heater, and Brady holds out his hands.

Soon his hands warm up. Energy moved from the heater to Brady's hands, and heat carried it.

Now let's follow the heater's wire to the wall plug. Energy moved from the wall plug to the heater, and electricity carried it along the wire.

And now the lamp lights Blake's page. Energy moved from the lamp to the page, and light carried it.

And now the bell rings, and Bennett hears it. Energy moved from the bell to his ear, and sound carried it.

So, the thing that carries energy from the giver to the receiver is called the carrier.

Finally, things that give out light usually give out heat too. The lamp lights Blake's page, and the lamp feels warm.

Okay, now your turn.

Here's Brady at lunchtime, on the sunny school steps with a mug of hot cocoa.

His hands warm up on the mug, and his face warms up in the Sun. Miss Murphy asks: what is touching your face?

The mug and Brady's hands touch, and heat carries the energy from the mug to his hands.

Now he holds his hands just above the mug. They touch nothing, and they still warm up: heat carries energy across the gap.

And nothing touches his face. The Sun is far away, and its light carries energy across the gap.

And now a drum booms across a field. It does not touch Bennett's ear, and sound carries the energy across the gap.

But electricity is different. It carries energy only along a wire from the giver to the receiver.

So, energy can move between two things that are not touching.

Okay, now your turn.

Here's everything we found out about how energy moves from one thing to another.

First, when energy moves, the thing it comes from is the giver, and the thing it goes to is the receiver.

The receiver is the thing that changes: it warms up, it is lit up, or the sound reaches it.

Next, the thing that carries energy from the giver to the receiver is called the carrier.

Sound, light and heat carry energy from one thing to another, and electricity carries energy along wires to whatever is plugged in.

Then, energy can move between two things that are not touching.

Light, sound and heat can carry energy across a gap, but electricity needs a wire from the giver to the receiver.

Okay, now your turn.

Here's Miss Fischer's class in the gym with a plastic bowling set.

Camden rolls the ball toward the pins. The pins stand still.

Then the ball hits the pins. The pins fly, you hear a loud clatter, and the ball slows down.

A moment ago, the pins were still. So what started them flying, and where did that clatter come from?

And if Camden rolls the ball faster next time, what will the pins do?

To find out, we will look at what a moving thing hands over when it hits something, and what happens to both things after the hit.

Okay, so are you ready to find out what happens when things bump into each other?

Here's Miss Fischer's class in the gym. Camden rolls a bowling ball toward the still pins.

The ball hits the pins. They fly, and the ball slows down. Where did the pins' energy come from?

The rolling ball is moving, so it has kinetic energy. At the hit, it hands over some of its energy.

Now the pins have energy, so they fly. The ball has less, so it slows down.

But now the ball rolls into the gutter and misses the pins. It hits nothing, so it hands over none of its kinetic energy, and the pins stay still.

And now a rolling shopping cart bumps into a parked cart and hands over some energy, so the parked cart starts rolling.

A moving object hands over some of its energy to whatever it hits. A moving object bumping into another object is called a collision.

Okay, now your turn.

Here's Miss Fischer's class with marbles out on the classroom floor. Brielle rolls a marble toward a still marble.

Before it arrives, Callie asks: what will each marble do?

The rolling marble hits the still marble. This hit is a collision. It hands over some of its energy to the still marble.

The still marble has energy now, so it starts moving. The rolling marble has less energy now, so it slows down.

And now, a toy car rolls into a still toy car. The still car starts moving, and the rolling car slows down.

And now, a skateboard rolls into a still skateboard. The still skateboard starts moving, and the rolling skateboard slows down.

Here's the pattern. When a moving object hits a still object, the still object starts moving and the moving object slows down.

Okay, now your turn.

Here's Miss Fischer's class with their marbles. Camden rolls a marble into a still marble, and they clack together. The still marble rolls only a little way.

Callie asks: where did the rest of the rolling marble's energy go?

You heard the clack. That sound carries energy from the marbles to your ears.

And now, Miss Fischer hammers a nail into a board. Each hit makes a bang, and that sound carries energy to your ears.

After ten hits, she touches the nail. It is warm: some of the hammer's energy warmed it, so the nail has more thermal energy.

Some went to the still marble, some into the sound, some into warmth. Nothing is gone.

So, here's what we've seen. In a crash, the sound carries some of the energy away, and some of the energy warms the two things that hit.

Okay, now your turn.

Here's Miss Fischer's class with a toy truck on a ramp and a block on the floor. Brielle says the truck has more energy when it's faster.

Camden says: you can't see energy. How can you tell?

We cannot see energy. But we can see what the truck hands over.

Brielle lets the truck go from the LOW mark. It is slow at the bottom, and the block slides 20 centimeters.

Now the same truck goes from the HIGH mark. Same block, same floor, so only the speed changes. It's faster at the bottom, and the block slides 55 centimeters.

The faster truck handed over more energy, so it had more. The slide is the evidence.

The faster object hands over more energy, so the block it hits slides farther. How far the block slides is the evidence that the faster object had more energy.

Okay, now your turn.

Here's everything we found out about what happens when things bump into each other.

First, a moving object hands over some of its energy to whatever it hits. A moving object bumping into another object is called a collision.

Next, when a moving object hits a still object, the still object starts moving and the moving object slows down.

Then, in a crash, the sound carries some of the energy away, and some of the energy warms the two things that hit.

And last, the faster object hands over more energy, so the block it hits slides farther. How far the block slides is the evidence that the faster object had more energy.

Okay, now your turn.

Here's Carla coming in from the snow, into Miss Hughes's warm classroom. Her hands are cold.

She wraps both hands around a mug of hot cocoa. Slowly her hands warm up, and the cocoa cools down.

Then she touches the metal leg of her chair, and it feels so cold. But the wooden seat does not feel cold, and both have stood in the same warm room all night.

Where did the heat from the cocoa go, and why does the metal feel colder than the wood?

To find out, we will look at which way heat moves, what happens to the temperatures, and why metal feels so cold.

Okay, so are you ready to follow the heat?

Here's Carla in Miss Hughes's classroom, her hand flat on the cold window. It feels cold.

Cedric says the cold is getting in. No. Nothing moves into her hand.

Her hand is hotter than the window, so heat moves from her hand to the window.

Heat leaves her hand, so it feels cold.

And now, a cold spoon in hot soup. The soup is hotter, so heat moves from the soup to the spoon.

And now, an ice cube in cold fridge water. The water is hotter, so heat moves from the water to the ice.

But now, a cup of water on the table all day. Both are the same temperature, so no heat moves.

So, here's the pattern. Heat moves from the hotter thing to the colder thing. If two things are the same temperature, no heat moves between them.

Okay, now your turn.

Here's Miss Hughes's class. A cup of warm water stands in a bowl of cold water, the same amount in each, a thermometer in each.

The cup's thermometer reads one hundred degrees Fahrenheit. The bowl's reads forty.

The cup's water is hotter, so heat moves from the cup to the bowl.

After five minutes, the cup's reads eighty-four degrees Fahrenheit. It went down.

The bowl's reads fifty-six degrees Fahrenheit. It went up.

After fifteen minutes, both read seventy degrees Fahrenheit, between forty and one hundred. The temperatures are the same, so heat stops moving.

A cold spoon in hot soup does the same. The soup's temperature goes down, and the spoon's goes up.

So, here's what we've seen. While heat moves, the hotter thing's temperature goes down and the colder thing's temperature goes up. When the two temperatures are the same, heat stops moving.

Okay, now your turn.

Here's Miss Hughes's class with two mugs of hot cocoa. Carla stirs with a metal spoon, Cedric with a wooden spoon.

After one minute, Carla's metal handle is hot. Cedric's wooden handle is still cool. Why is that?

Heat moves through the metal quickly, up to the handle. So it is hot.

Heat moves through the wood slowly. So the wooden handle stays cool.

And now, a hot potato in foil. Foil is metal, so heat moves through it quickly, and the outside is hot.

And now, a hot potato in a cloth napkin. Heat moves through the cloth slowly, so the outside stays cool.

A material that lets heat move through it quickly is called a heat conductor. A material that slows heat down is called a heat insulator.

So, here's the pattern. Metals are heat conductors. Wood, plastic and cloth are heat insulators.

Okay, now your turn.

Here's Celeste in Miss Hughes's classroom. She touches the metal leg of her chair, then the wooden seat. The leg feels colder.

Celeste says the metal is colder. Let's check with two thermometers.

Miss Hughes tapes a thermometer to each. Both read seventy degrees Fahrenheit, so the leg and the seat are the same temperature.

So why does the metal feel colder? Her hand is warmer, so heat moves out of her hand into both.

Metal is a heat conductor. Heat moves out of her hand into the metal quickly, and her hand feels cold.

Wood is a heat insulator. Heat moves into the wood slowly, so her hand still feels warm.

So, when a metal thing and a wooden thing are in the same room, they are the same temperature. Metal feels colder because it moves heat out of your hand faster.

Okay, now your turn.

Here's everything we found out about how heat moves from hot to cold.

First, heat moves from the hotter thing to the colder thing. If two things are the same temperature, no heat moves between them.

Next, while heat moves, the hotter thing's temperature goes down and the colder thing's temperature goes up. When the two temperatures are the same, heat stops moving.

Then, a material that lets heat move through it quickly is called a heat conductor. A material that slows heat down is called a heat insulator. Metals are heat conductors. Wood, plastic and cloth are heat insulators.

And last, a metal thing and a wooden thing in the same room are the same temperature. Metal feels colder because it moves heat out of your hand faster.

Okay, now your turn.

Here's Miss Novak's class on a night walk in the woods, flashlights off.

Colby's eyes are wide open, but he cannot see the trees, the path or his hands.

Then an owl hoots, deep and slow, and a bat squeaks overhead.

Colby hears both, from the dark. Nothing seemed to touch his ears, and nothing seemed to touch his eyes.

So what reaches Colby when he hears, and what fails to reach him when he looks?

To find out, we will look at what makes a sound high or low, loud or quiet, and what must reach your eye for you to see.

Okay, so are you ready to find out what reaches your ears and your eyes?

Here's Miss Novak's music lesson. Colby blows a whistle softly, and Colin taps a big drum softly.

Both are quiet, but they are not alike. So how are the two sounds different?

The whistle's sound is high, like a bird's tweet.

The drum's sound is low, like a dog's growl.

How high or low a sound is, is called its pitch. So the whistle's sound is high in pitch, and the drum's sound is low in pitch.

And now a bicycle bell rings. Its sound is high in pitch.

And now a cow moos. Its sound is low in pitch.

But now Colby blows the same whistle more softly. It is quieter, but still high in pitch: how loud a sound is does not change its pitch.

So, here's what we've seen. How high or low a sound is, is called its pitch.

Okay, now your turn.

Here's Colin at his desk with a ruler. A long part hangs over the edge, and he flicks it.

Its hum is low in pitch. Now he slides it in, so a short part hangs over, and flicks again.

The sound is higher in pitch. Same ruler, same desk, so why did the pitch change?

Every sound is made by something vibrating. The long part vibrates slowly, you can see it wobble, and its sound is low in pitch.

The short part vibrates faster, so fast that it is a blur, and its sound is higher in pitch.

And now Colin pulls a rubber band over a box tighter and plucks it: it vibrates faster, so its sound is higher in pitch.

The faster a thing vibrates, the higher in pitch its sound is.

The slower a thing vibrates, the lower in pitch its sound is.

Okay, now your turn.

Here's Cooper at a big drum, with grains of rice on its skin. He taps the drum gently, the rice hops a little, and the boom is quiet.

Now he hits the same drum hard. The rice jumps high, and the boom is loud.

Colby says the loud boom is higher in pitch. Is he right?

After the gentle tap, the skin vibrates only a little, so the sound is quiet.

After the hard hit, the skin vibrates strongly, so the sound is loud.

No, Colby is not right. Both booms are low in pitch, so the hard hit made the boom louder, not higher in pitch.

So, here's what we've seen. The more strongly a thing vibrates, the louder its sound is.

Hitting a drum harder makes its sound louder, not higher in pitch.

Okay, now your turn.

Here's Colby reading a book under a lamp. Miss Novak asks the class to draw the path the light takes.

Where do the arrows go? You see something only when light from it reaches your eye.

The lamp makes the light, so it is the light source, and the first arrow goes from the lamp to the book.

At the book, the light bounces off, just as it bounces off a mirror. This bouncing off is called reflection.

So the second arrow goes from the book to Colby's eye, and he sees the book.

And now Cooper looks at a tree in sunshine. The first arrow goes from the Sun to the tree, the second from the tree to his eye.

So, light travels from a light source to the thing, then bounces off the thing to your eye.

Okay, now your turn.

Here's Cooper in the basement, getting a box. It has no windows, and the bulb goes out.

His eyes are open, but he sees nothing, however long he waits. Why does he see nothing?

With the bulb on, light went from the bulb to the box, then to his eye.

With the bulb out, there is no light source. No light lands on the box, so none reaches his eye: he sees nothing.

Some people say eyes send out light. But they do not, or Cooper would see the box.

At night a bedroom is never completely dark: light from a streetlight comes in, and that is what you see by.

In a completely dark room, no light reaches your eye from anything, so you see nothing.

To hear a thing, a vibration must reach your ear. To see a thing, light must reach your eye.

Okay, now your turn.

Here's everything we found out about what reaches your ears and your eyes.

First, how high or low a sound is, is called its pitch. A whistle's sound is high in pitch, and a big drum's sound is low in pitch.

Next, the faster a thing vibrates, the higher in pitch its sound is. The slower a thing vibrates, the lower in pitch its sound is.

Then, the more strongly a thing vibrates, the louder its sound is. Hitting a drum harder makes its sound louder, not higher in pitch.

Then, light travels from a light source to the thing, then bounces off the thing to your eye.

And last, in a completely dark room, no light reaches your eye from anything, so you see nothing.

To hear a thing, a vibration from it must reach your ear. To see a thing, light from it must reach your eye.

Okay, now your turn.

Here's Miss Price's class at the park pond on a still morning.

Dana drops a stone in, and ripples spread out from the splash, ring after ring.

Far across the pond, a duck floats. The ripples reach it, and the duck starts to bob up and down.

But the duck does not float away: it bobs and stays right where it is. So what traveled across the pond to reach it?

To find out, we will look at what a ripple carries, how to tell one ripple from another, and how a pattern of flashes can carry a message.

Okay, so are you ready to follow the ripple across the pond?

Here's Miss Price's class at the park pond. Dana drops a stone in, and ripples spread out from the splash.

A duck floats near the far edge. The ripples reach the duck, and the duck bobs up and down.

Miss Price asks: did the water go with the ripple?

No, it did not. The duck bobs and stays in the same spot, so the water under it stays in the same spot too.

And now watch a leaf. The ripples pass under it, and the leaf bobs and stays over the dashed line.

The bump traveled across the pond, and it carried energy from the stone to the duck.

A bump that travels across the water is called a wave.

So, here's what we've seen. A wave carries energy across the water, and the water itself stays put, moving only up and down.

Okay, now your turn.

Here's Miss Price's class at the pond. Dana drops a small pebble, and little ripples spread out.

Then Declan drops a big rock, and his ripples are much bigger. The duck bobs higher.

Miss Price draws both waves from the side: wave A from the pebble, wave B from the rock. The dashed line is the middle line, the flat water before the wave came.

Wave B is taller than wave A. Its top is higher above the middle line.

And now an even bigger rock makes wave C. Wave C is taller than wave B.

But here is wave D, with its tops closer together. It is not taller than wave A: its top is the same height.

So, how tall a wave is, from the middle line up to its top, is called its amplitude. Wave B has a bigger amplitude than wave A.

Okay, now your turn.

Here's Dante at the edge of the pond, tapping the water with a stick, slowly: tap, tap, tap. Ripples spread out, with wide spaces between them.

Then he taps quickly, and the ripples come close together.

Miss Price draws both waves from the side, and they are the same height. So what changed?

Wave B's tops are closer together than wave A's.

And now even quicker taps make wave C. Wave C's tops are closer together than wave B's.

But here is wave D, which is taller. Wave D's tops are not closer together than wave A's: the space from one top to the next is the same.

So, the distance from the top of one wave to the top of the next is called its wavelength. Wave A has a longer wavelength than wave B.

Okay, now your turn.

Here's Miss Price at the board. She draws a wave and says: now draw me a wave taller than this one.

Dana, Dante and Declan each draw one, all different. Which one matches?

The words say taller, so the amplitude is bigger, and the wavelength is the same.

Dana's wave is taller, and its tops are the same distance apart, so it matches.

Dante's wave is taller, but its tops are closer together too, so the wavelength changed.

And Declan's wave is not taller: he changed the wavelength, not the amplitude.

A wave drawing is a pattern: the same bump, again and again, in the same way.

Now the words are: tops closer together. Only the wavelength changes; the height stays the same.

To draw a new wave, keep the same bump repeating, and change only what the words say: its amplitude, its wavelength, or both.

Okay, now your turn.

Here's the school playground, getting dark. Dana has walked to the far fence with a flashlight.

Before she went, the class agreed a code: short, short means yes, one long flash means no, and short, long, short means come here.

Miss Price calls: Dana, can you see us? Dana flashes short, short, and that means yes.

Dante calls: is it cold over there? One long flash comes back, and that means no.

Now Miss Price sends short, long, short, and Dana walks back: that means come here.

Every time Dana means yes, she sends the same pattern. The same pattern means the same word, so the class always knows.

And back inside, Declan taps short, short on his desk, and Dante reads it as yes.

So, a pattern of long and short flashes or taps can carry a message, when everyone agrees what each pattern means.

Okay, now your turn.

Here's everything we found out about how waves carry energy and messages.

First, a bump that travels across the water is called a wave.

A wave carries energy across the water, and the water itself stays put, moving only up and down.

Next, the amplitude of a wave is how tall it is, from the middle line up to its top.

Then, the wavelength of a wave is the distance from the top of one wave to the top of the next.

To draw a new wave, keep the same bump repeating, and change only what the words say: its amplitude, its wavelength, or both.

And a pattern of long and short flashes or taps can carry a message, when everyone agrees what each pattern means.

Okay, now your turn.

Here's Miss Walsh's class, with a battery, a bulb and two wires on every desk.

Derek clips one wire from the battery to the bulb, and nothing happens. With the second wire on, it lights up.

Then Miss Walsh takes a clip off the battery. Dexter puts a paper clip in the gap, and the bulb lights. Dominic tries a straw, and it stays dark.

Why did the bulb need the second wire, and why does the paper clip light it while the straw leaves it dark?

To find out, we will look at what a bulb needs, how to join one up, and which materials let electricity through.

Okay, so are you ready to make a bulb light?

Here's Derek with a battery, a bulb in a holder and two wires. He clips one wire from the battery to the holder, and the bulb stays dark.

Dexter says one wire is enough. He is not right.

Electricity flows around a loop: out of one end of the battery, through the bulb, and back to the other end.

With one wire there is a gap in the loop, so no electricity flows, and the bulb stays dark.

Now Derek clips a second wire from the other screw back to the other end of the battery. The loop is complete, so the bulb lights. Longer wires change nothing.

But now one clip slips off the battery. There is a gap again, so the bulb goes dark.

A complete loop like this is called a circuit. So, the bulb lights only when the loop is complete.

Okay, now your turn.

Here's Dominic in Miss Walsh's class. Two wires are clipped to his battery and his bulb holder, but the bulb stays dark.

Miss Walsh says, 'Follow the loop with your finger. Where does it stop?'

It stops at the battery. One clip rests on the battery's side, not on its end. That leaves a gap, so the bulb stays dark.

Dominic moves the clip onto the end. The loop is complete, so the bulb lights.

And now a clip sits on the bulb's glass. There is a gap at the holder's screw, so the bulb stays dark.

And now both clips are on one end of the battery. The other end is bare, so there is a gap, and the bulb stays dark.

If the loop is complete, the bulb lights. If there is a gap anywhere in the loop, the bulb stays dark.

Okay, now your turn.

Here's Derek with a battery, a bulb in a holder and two wires. Miss Walsh says, 'Make the bulb light.'

Step one. Clip one end of a wire to one end of the battery. You can start at either end.

Step two. Clip its other end to one screw of the holder. The loop still has a gap, so the bulb stays dark.

Step three. Clip one end of the second wire to the other screw.

Step four. Clip its other end to the other end of the battery. The loop is complete, so the bulb lights.

Then follow the loop with your finger to check it.

We build circuits with batteries only. Never put a wire into a wall's plug holes.

So, clip one wire from one battery end to one screw, and a second wire from the other screw to the other end.

Okay, now your turn.

Here's Dexter with a circuit that has a gap in one wire. The bulb is dark.

He puts a paper clip across the gap, and the bulb lights. Dominic puts a plastic straw across it, and the bulb stays dark. Why is that?

The paper clip is metal. Electricity passes through it, so the loop is complete, and the bulb lights.

Electricity cannot pass through the plastic, so the loop still has a gap, and the bulb stays dark.

A metal spoon goes across the gap, and the bulb lights. A wooden spoon goes across, and it stays dark.

One surprise: pencil lead is not a metal, but electricity passes through it.

A material that lets electricity pass through it is called an electrical conductor. A material that blocks electricity is called an electrical insulator.

Metals are electrical conductors. Plastic, wood and rubber are electrical insulators.

Okay, now your turn.

Here's everything we found out about how a circuit makes a bulb light.

First, a circuit is a complete loop from one end of the battery, through the bulb, back to the other end. The bulb lights only when the loop is complete.

Next, to find out if a bulb will light, follow the loop with your finger. If the loop is complete, the bulb lights. If there is a gap anywhere in the loop, the bulb stays dark.

Then, to build a circuit, clip one wire from one end of the battery to one screw of the bulb holder, and a second wire from the other screw back to the other end of the battery.

And last, a material that lets electricity pass through it is called an electrical conductor. A material that blocks electricity is called an electrical insulator. Metals are electrical conductors. Plastic, wood and rubber are electrical insulators.

Okay, now your turn.

Here's Miss Cruz's class, with a battery, two wires and a bulb on every desk.

Donna joins her parts into a loop, and the bulb lights up.

After a minute she touches the bulb, and it feels warm. Drew swaps his bulb for a buzzer, and the buzzer sounds.

But the battery just sits on the desk. So how does the energy get out of the battery, around the loop, and come out as light, heat and sound?

To find out, we will look at what each part of the circuit does, how the energy gets around the loop, and what comes out at the end.

Okay, so are you ready to follow the energy around the loop?

Here's Donna's desk: a battery, wires, a bulb and a switch in one loop, and a spare wire.

She presses the switch, and the bulb lights.

The battery has energy to give. Its job is to give the energy.

The wires join the parts into one loop.

Electricity flows through the bulb, and the bulb gives out light.

And now Donna presses the switch. It closes the gap, so the loop is complete. Pressed again, it opens a gap, so the switch is open and the loop is broken.

The switch makes no electricity. It only closes or opens the gap.

The spare wire, joined to nothing, has no job.

So, each part of a circuit has its own job. The battery gives the energy, the wires join the parts into one loop, the bulb gives out light, and the switch completes or breaks the loop.

Okay, now your turn.

Here's Drew's circuit on a long desk. The bulb sits far from the battery, on two long wires, and it lights.

Dylan says the bulb uses up the electricity. Miss Cruz asks how the energy gets from the battery to the bulb.

When the loop is complete, electricity flows all the way around it, and that flowing electricity is called the current.

The current carries energy from the battery to the bulb. The wire itself does not give energy.

Is Dylan right? No. Drew adds a matching bulb on the wire back to the battery, and both bulbs glow just the same.

The same current flows all the way round and back into the battery. The energy leaves the bulb with its light and heat.

So, the current carries energy from the battery to the bulb, and the same current flows on back to the battery.

Okay, now your turn.

Here's Miss Cruz's class with their loops. Donna's loop has a bulb in it, and the bulb lights.

The current carries energy from the battery to the bulb, and the bulb gives out light. Donna's finger near it feels warm, so the bulb gives out heat too.

And now Drew swaps his bulb for a buzzer. The current carries energy to the buzzer, and the buzzer gives out sound.

And now Dylan swaps his bulb for a motor with a fan. The current carries energy to the motor, and the motor gives out motion: the fan spins.

But now Dylan opens the switch. No current flows, so nothing carries energy to the motor, and the fan stops.

So, a working circuit gives out light, heat, sound or motion. A bulb gives out light and heat, a buzzer gives out sound, and a motor gives out motion.

Okay, now your turn.

Here's everything we found out about what a circuit gives out.

First, each part of a circuit has its own job.

The battery gives the energy, the wires join the parts into one loop, the bulb gives out light, and the switch completes or breaks the loop.

Next, the electricity flowing around the loop is called the current.

The current carries energy from the battery to the bulb, and the same current flows on back to the battery.

Then, a working circuit gives out light, heat, sound or motion.

A bulb gives out light and heat, a buzzer gives out sound, and a motor gives out motion.

Okay, now your turn.

Here's a school garden in winter, and two bird feeders hang from one branch.

Jack's feeder is painted bright red. Molly's feeder is plain brown.

A sparrow lands on Molly's feeder and eats. Then it hops to Jack's feeder, and the seed pours out onto the grass.

Jack's feeder looked better. So why did Molly's feeder work, and Jack's feeder fail?

Molly did something before she built hers, and Jack did not.

To find out, we will look at what a design must do, and how to check an idea before you build it.

Okay, so are you ready to build something that works?

Here's Miss Reyes's class, making bird feeders for the school garden. She says: before you build, write down what your feeder must do.

Jack writes: the feeder must be really good. Molly writes: the feeder must hold one cup of seed without spilling. Which line can you test?

Molly's line is a job the feeder must do. You can test it: pour in one cup of seed, and look for seed on the table.

Jack's line is not a job the feeder must do. Nobody can test really good.

Another line says: the feeder must hang from a branch by itself. That is a job. You can test it: hang it up, let go, and watch.

A job is something the design must do. Anyone can test a job: use the design, and watch what happens. A job the design must do is called a criterion.

Okay, now your turn.

Miss Reyes's class is making bird feeders. On the board she has written what a feeder must do: hold one cup of seed without spilling, and hang from a branch by itself. Something the design must do is called a criterion.

She adds a line: you may use only one plastic bottle, string and one wooden spoon. Liam asks for a second bottle, and she points at the new line.

Is the new line a criterion? No, it is not.

It says what you may use. It says nothing the feeder must do. It is a different kind of line: a limit you must stay inside.

So, a limit says what you may use, or how much time, space or money you have. You must stay inside a limit. A limit the design must stay inside is called a constraint.

Okay, now your turn.

Miss Reyes's class makes bird feeders. The board has two criteria, the jobs a feeder must do, and two constraints, the limits it must stay inside. Before anyone builds, the class checks every idea against the board.

Molly's first idea is a big hole near the bottom. The seed pours out, so it fails a criterion, and she crosses it out.

Her second idea is a small hole halfway up. It holds the seed, hangs by itself, and uses one bottle. It meets every criterion and stays inside every constraint, so she keeps it.

Liam wants a glass jar. That breaks the one-bottle constraint, so he crosses it out.

Write the criteria and the constraints down before you build. If an idea meets every criterion and stays inside every constraint, keep it. If an idea fails a criterion or breaks a constraint, cross it out.

Okay, now your turn.

Here's everything we found out about what a design must do and what it must stay inside.

First, a job the design must do is called a criterion. Anyone can test a criterion: use the design, and watch what happens.

Next, a limit the design must stay inside is called a constraint. A constraint says what you may use, or how much time, space or money you have.

Then, write the criteria and the constraints down before you build. If an idea meets every criterion and stays inside every constraint, keep it. If an idea fails a criterion or breaks a constraint, cross it out.

And nobody can test 'nicer', so 'make it nicer' is neither a criterion nor a constraint.

Okay, now your turn.

Here's Eden in Miss Torres's class on a windy morning. She holds her paper pinwheel out of the open window, and it spins so fast that you cannot see the blades.

Miss Torres watches it. Then she puts a paper cup on her desk and says, could that spinning lift this cup?

Eden is not sure. The pinwheel is only paper, and the wind is only air. But the wheel is turning, and turning can pull a thread.

To find out, we will look at what moving air and moving water can turn, where the energy goes, and how to build a design and test it.

Okay, so are you ready to build a wheel that lifts?

Here's Eden with her pinwheel out of the open window, and it turns fast. What pushes the blades round?

The moving air pushes on the blades, so the wheel turns.

Now a hair dryer blows at the pinwheel. The moving air pushes on the blades, so the wheel turns.

But with the window shut, the air is still. Still air does not push the blades round, so the wheel stays still.

Here's a spoon wheel under a pouring jug. The moving water pushes on the spoons, so the wheel turns.

Edgar says the wind is energy. Is he right? No, the wind is moving air, which has kinetic energy.

So, here's what we've seen. Moving air or moving water pushes on the blades of a wheel, so the wheel turns. Still air and still water do not push the blades round, so the wheel stays still.

Okay, now your turn.

Here's Miss Torres's desk, with Eden's pinwheel, a small electric fan, a flashlight and a spoon water wheel. She points the fan at the pinwheel, and it turns. Eliza says the pinwheel makes energy. Does it?

Energy comes in with the moving air. Energy goes out with the turning straw.

Now let's look at the fan. Energy comes in with electricity, along the wire. Energy goes out with the moving air.

And here is the flashlight's bulb. Energy comes in with electricity, from the battery. Energy goes out with the light.

A device that takes in energy with one thing and gives it out with another thing is called an energy changer.

So, is Eliza right? No, the pinwheel makes no new energy. The energy it gives out came in with the moving air.

Okay, now your turn.

Here's Miss Torres's class building energy changers. The board has one criterion, the job the design must do, and one constraint, the limit it must stay inside.

Eliza's pinwheel spins fast when she blows. Is her build finished? No, a spinning wheel on its own lifts nothing.

She draws her plan and checks it against the board. It can lift the cup, using only what the constraint allows.

Then she builds it step by step and blows. The wheel turns, the thread winds, and the cup rises.

Energy comes in with the moving air and goes out with the turning straw. Then it comes in with the turning straw and goes out with the rising cup.

Before you build, write down the criterion and the constraint, and check your plan against them. In an energy changer you build, each part hands energy to the next part.

Okay, now your turn.

Here's test day in Miss Torres's class. Eliza says Edgar's design looks the strongest, so his will lift the cup. How can the class tell?

A fair test changes only one thing, and here that one thing is the design. The same hair dryer blows from 30 centimeters at every wheel, with the same thread and cup.

Eden's wheel turns fast, the thread winds up, and the cup rises off the desk, so her design does the job.

Edgar's wheel turns slowly. The cup slides along and stays on the desk. So his design does not do the job yet.

Eliza's wheel does not turn, so her design does not do the job yet.

So, to test a design against the criterion, run the same fair test for every design, and say what happened. Only the test tells whether a design does the job.

Okay, now your turn.

Here's everything we found out about how to build and test an energy changer.

First, moving air or moving water pushes on the blades of a wheel, so the wheel turns. Moving air is a moving thing, so it has kinetic energy. So does moving water.

Next, a device that takes in energy with one thing and gives it out with another thing is called an energy changer. An energy changer makes no new energy.

Then, before you build, write down the criterion and the constraint, and check your plan against them. In an energy changer you build, each part hands energy to the next part.

And last, to test a design against the criterion, run the same fair test for every design, and say what happened. Only the test tells whether a design does the job.

Okay, now your turn.

Here's Elliott at the sink in Miss Castillo's classroom, washing a tray of odds and ends.

A cork and a candle sit at the top. A key and a marble lie at the bottom.

A big wooden ruler floats, and a tiny steel screw sinks.

So what decides which things float and which sink? And if you know what one piece of a material does, do you know what every piece does?

To find out, we will look at big pieces and small pieces of one material, at which materials float and which sink, and at how to pick out one sample by its properties.

Okay, so are you ready to find out how to tell materials apart?

Here's Miss Castillo's class, with two tubs of water on the table. Emery lowers a steel bolt in and lets go. It sinks.

Now she picks up a steel paperclip, tiny and light. Elliott says it will float, because it's so small. Is he right?

No, he's not right. The paperclip goes to the bottom. It sinks, just like the bolt. Both are steel.

Now, let's look at wood. Emilia lets go of a wooden block. It floats. Then she lets go of a tiny chip cut from the same block. It floats too. Both are wood.

And now, let's look at wax. A tall candle floats, with most of it under the water. A candle stub floats the same way. Both are wax.

So, here's what we've seen. Every piece of one material floats or sinks the same way, whatever its size or shape.

Okay, now your turn.

Here's Emery with two spoons, the same shape and size, one wood and one steel.

She says both will do the same thing. Is she right?

No. The wooden spoon floats, and the steel spoon sinks. Only the material is different.

Every piece of wood floats: wood is a floater. Every piece of steel sinks: steel is a sinker.

Miss Castillo puts one block on each pan: a wooden block and a steel block, the same size. The steel pan hangs lower: more mass, so steel is heavy for its size.

Wood is light for its size, so a log floats. A material heavy for its size is called dense. Steel is more dense than water.

Floating or sinking is a property of the material, not the object. A material that is heavy for its size sinks, and we say it is more dense than water.

Okay, now your turn.

Here's Miss Castillo's class. She holds a tray of six samples: a wooden block, a steel bolt, a glass marble, a cork, a stone and a candle.

She says: I'm thinking of one sample. It sinks, and a magnet pulls it.

First, Emery tests the first property in the water. The block, the cork and the candle float, so they're out. The bolt, the marble and the stone sink and stay in.

Next, Emilia tests the second property on the samples left. The magnet pulls the bolt, and not the marble or the stone, so they're out.

One sample is left: the steel bolt.

So, here's what we've seen. To find the sample that matches two properties, test the first property and cross out every sample that fails it. Then test the second property on the samples left. The one sample left matches both.

Okay, now your turn.

Here's everything we found out about how to tell materials apart.

First, every piece of one material floats or sinks the same way, whatever its size or shape.

Next, floating or sinking is a property of the material, not the object: wood is a floater, and steel is a sinker. A material that is heavy for its size sinks, and we say it is more dense than water.

And last, to find the sample that matches two properties, test the first property and cross out every sample that fails it. Then test the second property on the samples left. The one sample left matches both.

Okay, now your turn.

Here's Miss Diaz's class, getting snacks ready for a hike.

Enrique pours raisins and peanuts into a big bowl and stirs them. He can still see every raisin and every peanut.

Erica stirs a spoon of sugar into a jug of water for lemonade. She looks into the jug, and she cannot see the sugar anywhere.

But the raisins stayed in plain sight when Enrique stirred them. So where did Erica's sugar go, and is it still in the drink?

To find out, we will look at what Enrique made in his bowl, what happened to each snack in it, and where Erica's sugar went.

Okay, so are you ready to find out where the sugar went?

Here's Miss Diaz's class, getting snacks ready for a hike. Enrique pours raisins and peanuts into a bowl and stirs them. Erica's bowl holds raisins only.

Erica's bowl holds one kind of stuff. This is not a mixture.

But Enrique's bowl holds raisins and peanuts, stirred together. Two kinds of stuff are mixed together. This is a mixture.

And now Fern adds pretzels. Three kinds of stuff are mixed together. This is still a mixture.

And now Enrique shakes sand and water together in a jar. A solid and a liquid are mixed together. This is a mixture too.

But Fern's jar holds water only. It holds one kind of stuff. This is not a mixture.

So, here's what we've seen. When two or more materials are mixed together, what you get is called a mixture. One material on its own is not a mixture.

Okay, now your turn.

Here's Enrique's trail mix in Miss Diaz's class. Fern picks out one peanut.

Before mixing, this peanut was light brown, hard and crunchy. After mixing, it is still light brown, hard and crunchy. The peanut is still a peanut.

And now look at a raisin. After mixing, it is still dark, wrinkly and sweet. The raisin is still a raisin.

And now look at the jar of sand and water. The sand still lies on the bottom in tan grains, and the water is still clear. Each one is still itself.

And now steel paper clips are mixed with glass marbles. The magnet still pulls the paper clips, and not the marbles. Each one is still itself.

So, in a mixture, each material is still itself. Each material keeps its own properties, so you could get each part back again.

Okay, now your turn.

In Miss Diaz's class, Erica stirs sugar into water, and Fern stirs sand into water. Both glasses are mixtures.

In Fern's glass, the sand lies on the bottom. You can see the parts.

But in Erica's glass, the sugar broke into pieces too small to see and spread all through. You cannot see the parts.

And now salt is stirred into water. It spreads all through in pieces too small to see. You cannot see the parts.

And now one drop of red food coloring spreads through water until it is pale red. You cannot see the parts.

But now a spoon of oil goes into water. It floats on top in a layer. You can see the parts.

So, a solution is a mixture where a solid or a liquid is mixed into a liquid so well that you cannot see the parts.

Okay, now your turn.

Here's Erica's lemonade. She stirred sugar into the water, and now nobody can see it. Enrique says the sugar disappeared. Fern says it melted.

The sugar broke into pieces too small to see and spread all through the water. When a material does that, we say it dissolves.

Is the sugar gone? No. In science, we don't taste things to observe them, but this lemonade is a drink Miss Diaz made, so Erica takes a sip. It tastes sweet, and the sweet taste is the sugar. The sugar is still there.

And now salt dissolved in water tastes salty, so the salt is still there.

Did the sugar melt? No. Melting is when a solid warms up enough and turns into a liquid. The sugar did not warm up. It dissolved.

So, a dissolved material is not gone. It is still there, in the liquid.

Okay, now your turn.

Here's everything we found out about what mixtures and solutions are.

First, when two or more materials are mixed together, what you get is called a mixture.

One material on its own is not a mixture.

Next, in a mixture, each material is still itself.

Each material keeps its own properties, so you could get each part back again.

Then, a solution is a mixture where a solid or a liquid is mixed into a liquid so well that you cannot see the parts.

One material breaks into pieces too small to see and spreads all through the liquid.

And last, when a material breaks into pieces too small to see and spreads all through a liquid, we say it dissolves.

A dissolved material is not gone. It is still there, in the liquid.

Okay, now your turn.

Here's Miss Vance's class on a hike, stopping for a snack.

Finley opens his backpack, and his bag of tortilla chips is all crumbs. 'There's less of it now,' he says.

Fiona shakes drink powder into her bottle of water and stirs. Soon she cannot see the powder. 'That's gone too,' says Finley.

But is there really less chip in the bag, and did the powder go anywhere at all?

Back at school, a digital scale can settle it.

To find out, we will look at what happens to the mass when a thing breaks into pieces, and when two things are mixed together.

Okay, so are you ready to put it on the scale?

Here's Miss Vance's scale. She puts a whole chocolate bar on the pan: forty-five grams.

Fiona snaps the bar in four and puts every piece back. Frances says the pieces are lighter. What will the scale read?

It reads forty-five grams again. The pieces are the same stuff, just broken up. No stuff was added, and no stuff was taken away.

Finley crumbles a cracker that read eight grams. Every crumb goes onto the pan: eight grams again.

Frances pulls a ball of clay, sixty grams, into five little balls. Spread out on the pan, they read sixty grams again.

But if one crumb falls on the floor, that stuff is off the pan, and the scale reads a little less.

So, when you break a thing into pieces, the mass stays the same. No stuff was added, and no stuff was taken away.

Okay, now your turn.

Here's Finley at Miss Vance's table with his ball of clay in three pieces, and the digital scale.

He puts each piece on the scale in turn: twenty-five grams, twenty grams, fifteen grams.

Miss Vance asks: what will the scale read with all three pieces on it?

The whole ball is the three pieces together, so add the three masses: twenty-five plus twenty plus fifteen makes sixty grams.

Finley puts all three pieces on, and the display stops at sixty grams.

And now a whole bar, forty-five grams, goes on one pan of a balance, and two pieces of a second bar, thirty grams and fifteen grams, go on the other. The pans hang level.

So, to find the mass of the whole, add the masses of the pieces together. The whole and its pieces balance, because their masses are the same.

Okay, now your turn.

Here's Miss Vance's class making bean-bag filling. Frances has a cup of rice and a cup of beans.

The cup of rice reads one hundred eighty grams, the cup of beans two hundred grams, and together three hundred eighty grams.

Frances pours the beans into the rice. Finley says mixed together there is more. What will the scale read?

It reads three hundred eighty grams again. The rice is still rice, and the beans are still beans, so no stuff was added or taken away.

And now Fiona stirs a small cup of sugar, twenty grams, into a cup of water, two hundred fifty grams. The sugar dissolves but is still there, so the scale reads two hundred seventy grams.

So, when things are mixed together, the mass of the mixture is the masses of the parts added together. Each material is still itself.

Okay, now your turn.

Here's everything we found out about why the mass stays the same.

First, when you break a thing into pieces, the mass stays the same. No stuff was added, and no stuff was taken away.

Next, to find the mass of the whole, add the masses of the pieces together. The whole and its pieces balance, because their masses are the same.

Then, when things are mixed together, the mass of the mixture is the masses of the parts added together. Each material is still itself, so the mass stays the same.

Okay, now your turn.

Here's Miss Mendez's class, camping at a state park. As the sun sets, she strikes a match and lights the campfire.

The match burns down to a black, crumbly stick, and smoke drifts up.

Frankie opens the cooler. The ice she packed this morning has turned into cold water.

Gabriel says the match and the ice both changed. So are those two changes the same kind, or two different kinds?

To find out, we will look at ice, water and water vapor, at changes that make a new material or keep the same material, and at the clue that tells them apart.

Okay, so are you ready to find out when a change makes a new material?

Here's Miss Mendez's class at a state park campout. This morning Frankie packed a frozen water bottle to keep her sandwich cold.

At lunchtime the bottle is half ice, half water. Gavin says half her ice is gone. Is he right?

He's half right: the sun warmed the bottle, so half the ice melted. But it didn't go anywhere: it's water now, still in the bottle.

Ice is water as a solid. The water in the bottle is water as a liquid. Water vapor is water as a gas. All three are the same stuff: water.

And each state has its jobs. Solid water keeps food cold, liquid water is for drinking and washing, and water vapor cooks food in a steamer.

So, here's what we've seen. Ice, water and water vapor are the same stuff, water, in three states: solid, liquid and gas.

Okay, now your turn.

Here's Miss Mendez's class at their campout. She strikes a match and lights the campfire. The match burns down to a black, crumbly stick, and smoke drifts up.

Frankie says the wood just disappeared. Is she right?

No, she's not right. The wood turned into ash and smoke. Ash and smoke are not wood: they are new materials.

And now the ice in the cooler turned into water. But water is the same material as ice, so nothing new formed.

A nail rusts: rust is a new material. Cake batter bakes: the cake is a new material.

Paper cut into strips is still paper. Sugar dissolved in water is still sugar, mixed in.

So, here's what we've seen. Some changes turn a material into a new material. Other changes keep the same material, in a new state, a new shape or mixed into something else.

Okay, now your turn.

At Miss Mendez's class campout, Frankie finds an old nail on the picnic table, red-brown and flaky.

Gabriel says it's just dirty, so Frankie rubs it. The red-brown stays. Is it dirt?

No, it's not dirt, because dirt wipes off. This is rust, a new material. Its new color will not change back, and that is the clue.

And now a week-old banana has turned brown and soft and smells strong. A new color and a new smell are clues.

A fizzing tablet drops into water, and bubbles rush up: another clue.

But a frozen puddle melts back into water by noon. It changed back, so nothing new formed.

So, here's what we've seen. The clue that a new material formed is a changed property that will not change back: a new color, a new smell, bubbles, or a new kind of solid.

Okay, now your turn.

Here's everything we found out about when a change makes a new material.

First, ice, water and water vapor are the same stuff, water, in three states: solid, liquid and gas. We use water in every state: solid water keeps food cold, liquid water is for drinking and washing, and water vapor cooks food in a steamer.

Next, some changes turn a material into a new material. Other changes keep the same material, in a new state, a new shape or mixed into something else.

And last, the clue that a new material formed is a changed property that will not change back: a new color, a new smell, bubbles, or a new kind of solid.

Okay, now your turn.

Here's Gloria at Enchanted Rock in Texas, a huge pink dome of rock.

She picks up a loose chunk. Up close, it has white bits, glassy gray bits, and black bits that glitter in the sun.

Her dad says it is one rock. But it looks like lots of little pieces stuck together. So is a rock one thing, or many?

And if it is many things, Gloria would need a way to tell them apart.

To find out, we will look at how to describe a rock, what rocks are made of, and how to test the pieces inside.

Okay, so are you ready to find out what a rock is made of?

Here's Hadley and Heidi in Miss Burke's class. Each has a gray rock and has written 'gray and hard'.

Miss Burke holds up the two rocks. Which rock is whose?

Nobody can tell, because 'gray and hard' fits both.

So let's look closer, like a geologist does.

Here is a chunk of granite. It is pink, white, gray and black, all speckled together.

The small pieces you can see in a rock are called grains. In granite, the grains are big enough to see.

Hadley feels the granite, and it is rough. He turns it, and the black flecks glitter.

And now here is sandstone. It is red-brown, you can just see its grains, it feels gritty, and it is dull.

So, to describe a rock, say its colors, whether you can see its grains, how it feels, and whether it is shiny or dull.

Okay, now your turn.

Here's Gloria in Miss Burke's class with a chunk of granite and a magnifying glass. Is the rock one thing, or lots of little pieces stuck together?

No, the rock is not one thing. Through the glass, Gloria sees three kinds of grain: pink, glassy gray, and black flakes that glitter.

Each grain is one kind of stuff, the same all the way through. One kind of stuff like this is called a mineral.

The pink mineral is feldspar, the glassy gray mineral is quartz, and the black flaky mineral is mica.

Think of a cookie. A cookie is made of flour, sugar and chocolate chips.

In the same way, granite is made of feldspar, quartz and mica.

So, a rock is made of grains of minerals. A mineral is one kind of stuff a rock is made of, the same all the way through.

Okay, now your turn.

Here's Hadley in Miss Burke's class with two white minerals. One is quartz and one is calcite, but which is which?

Both minerals are white, and both look shiny like glass.

How shiny a mineral looks is called its luster, and it is the same for both.

So Hadley tests what can scratch them, because what can scratch a mineral tells you its hardness.

A penny scratches one mineral, and nothing scratches the other.

Miss Burke's chart says a penny scratches calcite, so that one is calcite, and the other is quartz.

Now Hadley rubs pyrite across a white tile.

The color of the mark is called its streak. Pyrite looks like gold, but its streak is greenish black.

So, to tell a mineral apart, test it: its color, its luster, its hardness and its streak, and write each result in a table.

Okay, now your turn.

Here's everything we found out about what a rock is made of.

First, the small pieces you can see in a rock are called grains. To describe a rock, say its colors, whether you can see its grains, how it feels, and whether it is shiny or dull.

Next, a rock is made of grains of minerals. A mineral is one kind of stuff a rock is made of, the same all the way through.

And last, how shiny a mineral looks is called its luster. What can scratch a mineral tells you its hardness. The color of the mark a mineral leaves on a white tile is called its streak.

So, to tell a mineral apart, test it: its color, its luster, its hardness and its streak, and write each result in a table.

Okay, now your turn.

Here's Jace at the edge of the Grand Canyon with his family. The far wall is striped: flat layers of red and tan rock, one on top of another.

In his pocket is a black rock he picked up in Hawaii last summer. It has no stripes at all: it's dark and smooth, with grains too small to see.

Two rocks, and they could not look more different. Were the canyon's stripes painted on? And was Jace's black rock ever hot?

To find out, we will look at rocks made from melted rock, and rocks made from sand, mud and shells pressed together.

Okay, so are you ready to find out how a rock is made?

Here's Miss Lopez's class, with a tray of rocks. Ian picks up a speckled rock, and Isaac picks up a smooth black one. Miss Lopez says they're in the same family. What do they have in common?

Ian's rock is granite. Its grains are pink, white, gray and black, locked together with no gaps. It's hard, with no layers.

Isaac's rock is obsidian. It has no grains you can see, even up close: it's smooth, like black glass. It's hard, and it has no layers.

Here's basalt, from Hawaii. Its grains are too small to see, but they're locked together, and it has no layers.

But Jace's rock has flat layers, and its sand grains rub off. So it's not in this family.

So, here's what we've seen. Igneous rock is hard, with grains locked together or smooth like glass, and it never has layers.

Okay, now your turn.

Here's Jace in class with a black rock from Hawaii. Miss Lopez says it was once a liquid. Isaac says that can't be right: rock is hard. Is she right?

Yes, she is. Deep inside Earth, some rock is so hot it has melted. When a volcano erupts, that melted rock pours out as lava.

In the air, the lava cools and hardens into dark rock. Jace's rock is a piece of that lava, cooled long ago, so it's as cool as the ground.

Lava in the air cools fast, so its grains are tiny, or it turns to glass. Deep underground, melted rock cools slowly, so its grains are big. Once it's hard, the grains stay as they are.

So, here's what we've seen. Igneous rock forms when melted rock cools and hardens. Fast cooling gives tiny grains or glass; slow cooling gives big grains.

Okay, now your turn.

Here's Miss Lopez's class at the tray. Jace's rock has flat stripes, and Ian's rock is full of shells. Miss Lopez says they're in one family too. What do they have in common?

Jace's rock is sandstone: sand grains pressed together. A grain rubs off, so the grains are not locked. The stripes are flat layers, right through the rock.

Ian's rock is limestone. Pieces of shell are pressed in among tiny grains, and it has flat layers.

Here's shale: gray mud pressed into thin flat layers. And conglomerate: round pebbles pressed together in sand. But granite is not in this family: its grains are locked, and it has no layers.

Sand, mud and shell that settle in water are sediment. So, here's what we've seen. Sedimentary rock is made of grains or pieces pressed together, often in flat layers, sometimes with shells inside.

Okay, now your turn.

Here's Ian's limestone from a Texas hill, far from the sea, full of shells. How did sea shells get inside a rock on a hill?

Miss Lopez shakes a jar of water, sand, mud and pebbles, then lets it stand. The pieces settle in flat layers: pebbles, sand, then mud. Settled pieces are sediment. They're still loose: making rock takes many more layers, and a very long time.

In the sea, it's the same. Sand and mud settle in a layer. More layers settle on top and press down. Over a very long time, the pieces stick together as rock.

Long ago, a sea covered that part of Texas. Shells settled on its floor, layer on layer, and were pressed into limestone.

So, here's what we've seen. Sedimentary rock forms when small pieces settle in layers, get pressed together and stick, over a very long time.

Okay, now your turn.

Here's everything we found out about how igneous and sedimentary rock form.

First, igneous rock is hard, with grains locked together or smooth like glass, and it never has layers.

Next, igneous rock forms when melted rock cools and hardens. Fast cooling gives tiny grains or glass; slow cooling gives big grains.

Then, sedimentary rock is made of grains or pieces pressed together, often in flat layers, sometimes with shells inside.

And last, sedimentary rock forms when small pieces settle in layers, get pressed together and stick, over a very long time.

Okay, now your turn.

Here's Miss Garcia's class on the steps of the old courthouse.

The steps are white stone with gray wavy stripes, the roof is dark gray stone, and the walls are speckled granite.

Miss Garcia says two of these rocks were once a completely different rock. Jada looks at the hard white step and cannot believe it.

Which two rocks changed, and what could change a rock?

And under the town, one rock holds water like a sponge.

To find out, we will look at wavy stripes in rocks, heat and squeezing, sorting rocks into families, and which rocks hold water and oil.

Okay, so are you ready to sort the rocks?

Here's Miss Garcia's class with the rock box. Jasper holds up a gray rock with dark and light stripes, next to Jana's sandstone.

Jasper says the stripes are layers, so the rock is sedimentary. But look closer: the stripes bend and wave.

Sandstone's layers are flat and straight, with sand grains stuck together. These stripes are wavy bands of grains.

Granite's grains are the same, but locked together in a jumble, with no bands.

And here is slate. Its grains are too small to see, but they all lie lined up the same way, so slate splits into thin, flat sheets.

And here is marble. Its grains sparkle like sugar, and gray wavy stripes cross the white.

So, here's what we've seen. Metamorphic rock has bands or wavy stripes, or grains lined up so it splits into flat sheets. It is often hard and often shiny.

Okay, now your turn.

Here's Jada at a marble quarry in Vermont. The guide says this marble was once limestone, a soft gray rock with shell pieces inside.

How can that be? Over a very long time, rock piles on top, so the limestone ends up deep underground.

The rock above presses in from every side, so the limestone is squeezed. And deep underground it is hot.

Heat and squeezing change the grains. The shell pieces turn into new grains, and the limestone has become marble.

But the limestone stayed solid the whole time. A rock that melts, then cools and hardens, is igneous.

Shale, a soft gray rock made of mud, changes the same way into slate, a hard rock that splits into smooth sheets.

So, here's what we've seen. Metamorphic rock forms when heat and squeezing deep underground change a rock into a new rock, without melting it.

Okay, now your turn.

Here's Miss Garcia's class sorting the rock box into three piles: igneous, sedimentary and metamorphic. Jada holds up a striped rock.

Every rock gives a clue in its grains. This rock has grains locked in a jumble. So this rock is igneous.

And this rock has sand grains stuck together in flat, straight layers. So this rock is sedimentary.

And this rock has dark and light bands that bend and wave. So this rock is metamorphic.

Now let's look at Jada's rock. Its stripes are flat, straight layers of sand grains stuck together. So Jada's rock is sedimentary.

So, here's what we've seen. To sort a rock into its family, look at its grains. Grains locked in a jumble, or a glassy look, mean igneous. Pieces stuck together in flat layers mean sedimentary. Bands or wavy stripes, or grains lined up in flat sheets, mean metamorphic.

Okay, now your turn.

Here's Miss Garcia dripping water onto a sandstone and a granite. The sandstone's drop soaks in and the rock turns dark. The granite's drop stays on top in a bead.

Where did the water go? Close up, the sand grains are stuck together, but tiny spaces sit between them, and the water went into the spaces.

A sponge has tiny spaces too, so it holds water.

Granite's grains lock together with no spaces, so the water stays on top.

Deep under Texas, limestone with tiny spaces holds oil, and sandstone holds water and natural gas. The oil sits in the tiny spaces, not in an underground lake.

So, here's what we've seen. A rock with tiny spaces between its grains, like sandstone or limestone, can hold water, oil or natural gas, like a sponge. A rock with no spaces, like granite or slate, cannot.

Okay, now your turn.

Here's everything we found out about the three rock families.

First, metamorphic rock has bands or wavy stripes, or grains lined up so it splits into flat sheets. It is often hard and often shiny.

Next, metamorphic rock forms when heat and squeezing deep underground change a rock into a new rock, without melting it.

Then, to sort a rock into its family, look at its grains. Grains locked in a jumble, or a glassy look, mean igneous. Pieces stuck together in flat layers mean sedimentary. Bands or wavy stripes, or grains lined up in flat sheets, mean metamorphic.

And a rock with tiny spaces between its grains, like sandstone or limestone, can hold water, oil or natural gas, like a sponge. A rock with no spaces, like granite or slate, cannot.

Okay, now your turn.

Here's Miss Ramos's class on a hilltop trail in a state park. A big gray boulder sits beside the path, with a crack down it and pieces of rock lying beside it.

Far below, the river winds through the valley and flows into a lake. Where the river meets the lake, a flat fan of pale sand spreads out into the water.

Jenna looks at the sand, then at the boulder. She asks: did that sand down there come from this rock up here?

To find out, we will look at how rock breaks, how the pieces travel, and where they come to rest.

Okay, so are you ready to find out how rock breaks, moves and settles?

Here's Miss Ramos's class on a hilltop trail in a state park. A big gray boulder sits beside the path, with a crack down it and pieces of rock lying right beside it. Jesse says somebody must have smashed it. Is he right?

No, he's not right. Nobody smashed it. Over many years, the rock slowly broke apart by itself, and the pieces stayed right where the rock sits.

And now consider an old stone wall. Its top stones crumbled, and the chips lie along the wall's base. The stones broke, and the pieces stayed in place.

When rock breaks into smaller pieces right where it sits, we call it weathering.

So, here's what we've seen. Weathering breaks rock into smaller pieces right where the rock sits. The pieces stay in place.

Okay, now your turn.

Here's Miss Ramos's class at a cracked concrete sidewalk slab. Concrete is sand and small stones stuck together, so it breaks like rock. A thick tree root has grown into the crack. Joel says a root is too soft to break rock. Is he right?

No, he's not right. Each year the root grew thicker and pushed the crack wider. The root broke the rock, so the root did the weathering.

And now, here's the hilltop boulder again. Rain water ran into a thin crack. On a cold night it froze into ice, and the ice took more room, so it pushed the crack wider.

Winter after winter the crack grew, and the boulder broke. Ice did the weathering.

So, here's what we've seen. Plant roots and ice both push a crack in rock wider. They do the weathering.

Okay, now your turn.

Here's Miss Ramos's class crossing a small stream. The stream runs over a flat rock, and the rock has a smooth groove worn across its top. Jenna says water is too soft to wear away rock. Is she right?

No, she's not right. The running water wears a tiny bit off the rock every day. After many years, the tiny bits add up to a groove. Water did the weathering.

And now, in a windy desert, blown sand scrapes bits off a rock. Wind did the weathering.

And last, hot days and cold nights make a mountain rock swell a little and shrink a little, so flakes come off. Heat and cold did the weathering.

So, here's what we've seen. Water, ice, heat and cold, wind and plant roots all break rock into smaller pieces. They do the weathering.

Okay, now your turn.

Here's Miss Ramos's class back at the hilltop boulder, the morning after heavy rain. The grit that lay beside the boulder is gone, and the big pieces are still there. Jenna says the pieces disappeared. Is she right?

No, she's not right. The rain water ran down the slope and carried the grit down into the river. The grit broke off up here, and now it lies somewhere new.

And now consider a dry, dusty field. A strong wind picks up the dust and carries it far away, across the valley.

But pieces lying right beside the rock they broke from have not been carried. That is weathering.

When the broken pieces are carried away to somewhere new, we call it erosion.

So, here's what we've seen. Erosion carries the broken pieces away to somewhere new.

Okay, now your turn.

Here's Miss Ramos's class by the river. A tall cliff stands over the path, with a heap of rocks at its foot. Jesse says the river carried those rocks here. Is he right?

No, he's not right. The heap is at the cliff's foot, not by the river. The rocks fell a long way down from where they broke. Earth pulled them down, so Earth's pull did the erosion.

And now the river carries sand along, far downstream. Moving water did the erosion.

Next, wind picks up beach sand and blows it along. Wind did the erosion.

And last, a glacier is a river of ice that slides downhill very slowly. Rocks stuck in the ice go with it. The ice did the erosion.

So, here's what we've seen. Moving water, wind, ice and Earth's pull all carry the pieces away. They do the erosion.

Okay, now your turn.

Here's Miss Ramos's class where the river meets the lake. A flat fan of sand spreads into the water. Joel says the river is still carrying this sand. Is he right?

No, he's not right. The sand lies still. Up the hill, the fast river carried it. At the lake it slowed down, so it dropped the sand right here.

And now, wind carries sand along a beach. At a bush it slows down and drops the sand in a pile.

Next, a glacier melts at its end, so it drops its rocks in a heap.

But sand in a fast river is still moving. That is still erosion.

When carried pieces are dropped in a new place, we call it deposition.

So, here's what we've seen. Deposition is the dropping of the carried pieces in a new place, when the carrier slows down or melts.

Okay, now your turn.

Here's Miss Ramos's class at the end of the trail. Miss Ramos asks about the big pieces beside the cracked boulder. Jenna says those pieces moved when they broke off, so that is erosion. Is she right?

No, she's not right. Those pieces have not been carried anywhere. So that is weathering, not erosion.

Ice widens a crack in a boulder. The rock broke where it sits, so this is weathering.

Flood water carries soil off a field. The pieces were carried away, so this is erosion.

Mud settles on a river's bend. The pieces were dropped in a new place, so this is deposition.

So, here's the pattern. Ask what happened to the rock. If it broke where it sits, that is weathering. If its pieces were carried away, that is erosion. If the pieces were dropped in a new place, that is deposition.

Okay, now your turn.

Here's everything we found out about how rock breaks, moves and settles.

First, weathering breaks rock into smaller pieces right where the rock sits. The pieces stay in place.

Plant roots and ice both push a crack in rock wider. They do the weathering.

Water, ice, heat and cold, wind and plant roots all break rock into smaller pieces. They do the weathering.

Next, erosion carries the broken pieces away to somewhere new.

Moving water, wind, ice and Earth's pull all carry the pieces away. They do the erosion.

Then, deposition is the dropping of the carried pieces in a new place, when the carrier slows down or melts.

And last, to sort a change, ask what happened to the rock. If it broke where it sits, that is weathering. If its pieces were carried away, that is erosion. If the pieces were dropped in a new place, that is deposition.

Okay, now your turn.

Here's Jordan at the Grand Canyon with his dad. The walls drop down and down, striped with flat layers of rock.

Near the top, his dad shows him a rock with a sea shell pressed in it, high above any sea.

Jordan wonders which stripe came first, and how a sea shell got up here.

Rock layers can't tell you the time of day. But they can tell you which came first, and which came later.

To find out, we will look at which layer formed first, how old a fossil is, and how the layers tell a place's story.

Okay, so are you ready to find out how rock layers tell the time?

Here's Miss Ruiz's class at a road cut in Texas, where the rock face has four flat stripes.

Karl asks, did the stripes all form at the same time, or did one form first?

Now consider a sea floor long ago. A river drops sand and mud, which settle in one flat layer.

Later, more pieces settle, and they can only land on top of the first layer, because it is already there.

Later still, a third layer lands on top, after hundreds or thousands of years.

Today the layers are rock in a cliff. The bottom layer landed first, so it is the oldest; the top landed last, so it is the youngest.

So, in rock layers that still lie flat, the bottom layer formed first. Each new layer of pieces landed on top of the layers already there, so a deeper layer is older.

Okay, now your turn.

Here's Julia at the road cut, drawing the rock face. She counts five stripes, with a stripe of soil on top.

Miss Ruiz asks, which stripe formed first, which second, and so on to the last?

The bottom layer formed first, so Julia writes 1 beside it.

The layer above landed on top of layer 1, so it formed next, and Julia writes 2.

Then she writes 3 on the next layer up, and 4 on the one above.

The soil on top landed last of all, so it gets 5.

Now consider a cliff with three layers. From the bottom, the tan sand is 1, the gray mud is 2, and the cream rock is 3.

So, to put rock layers in time order, start at the bottom layer and count up. The bottom layer formed first, and the top layer formed last.

Okay, now your turn.

Here's Karl with a shell fossil from the road cut's bottom stripe. Jordan has a leaf print from the top stripe.

Which is older, the shell or the leaf?

Now consider a shell on the sea floor long ago. Small pieces settle on it, bury it, and become the shell's layer.

So the shell fossil is about as old as its layer.

Jordan thinks the heavy shell sank down through the rock. No, rock is solid, so nothing sinks through it.

The shell's layer is at the bottom, so it formed first. The leaf's layer is on top, so it formed last, and the shell is older.

So, a fossil is about as old as the rock layer it sits in, because that layer's pieces buried it as they settled. A fossil in a deeper layer is older than a fossil in a layer above it.

Okay, now your turn.

Here's Miss Ruiz's class at a hillside a river cut into: shells at the bottom, then sand, then soil with roots on top.

What was this place like long ago, and how did it change?

A fossil shows what lived in a place long ago, and sea shells come from sea animals.

Each layer formed at a different time, so read them from the bottom up.

Layer 1 holds sea shells, so the place was under the sea. Layer 2 is sand, so it was a sandy shore.

Layer 3 is soil with tree roots, so it was a forest. So the sea came first, then a sandy shore, then a forest.

So, to read a landscape's story, read each layer from the bottom up, and say what the place was like when that layer formed. Those changes, in that order, tell how the place changed.

Okay, now your turn.

Here's everything we found out about how rock layers tell the time.

First, in rock layers that still lie flat, the bottom layer formed first. Each new layer of pieces landed on top of the layers already there, so a deeper layer is older.

Next, to put rock layers in time order, start at the bottom layer and count up. The bottom layer formed first, and the top layer formed last.

Then, a fossil is about as old as the rock layer it sits in, because that layer's pieces buried it as they settled. So a fossil in a deeper layer is older than a fossil in a layer above it.

And last, to read a landscape's story, read each layer from the bottom up, and say what the place was like when that layer formed. Those changes, in that order, tell how the place changed.

Okay, now your turn.

Here's Kendra in the school library in Oklahoma. The lamps swing, the books wobble, and the floor hums for about twenty seconds. Then it stops.

Later, the news says the earthquake started under a town a hundred miles away.

But what is under the floor that shook? And how did the shaking travel a hundred miles to the library?

To find out, we will look at the rock under the ground, how the shaking spreads out, and how to test which building design protects better.

Okay, so are you ready to find out what happens in an earthquake?

Here's Miss Perez's class beside a road cut, where a hill was cut away for the road. Kendra asks: how far down does the dirt go?

At the top there's a thin band of soil, about as deep as Keegan is tall. Under it, gray rock goes all the way down to the road.

Now let's look under a city street. Under the street there's pavement, then soil, then rock.

And what is under the sea? Under the water, there's rock too. Dig down anywhere on Earth, and you reach rock.

All that rock joins up into one hard shell around the whole Earth. Earth's hard rocky outer shell is called the crust.

So, the ground is the top of Earth's hard rocky outer shell, called the crust. The soil is only a thin layer on top of the rock.

Okay, now your turn.

Here's Kyla in her kitchen. The glasses rattle for twenty seconds: an earthquake. Then her cousin, fifty miles away, calls: he felt it too. How did the shaking reach him?

Here is a pond. A wave carries energy across it, and the water stays put.

Deep in the crust, two huge pieces of rock push together and stick. Then, suddenly, they slip. The earthquake starts there.

The slip shakes the rock next to it, and so on. The shaking spreads out through the crust as waves, for miles.

Near the slip, the waves shake the ground hard. Far away, they shake it gently. The ground at each town shakes in place; it does not travel.

So, an earthquake starts where rock deep in the crust suddenly slips. The shaking spreads out through the crust as waves, so the ground shakes far from where the rock slipped.

Okay, now your turn.

Here's Miss Perez's class at a shaking table, a board that slides back and forth. Keegan and Kendra each built a tower of blocks. The tower must stay standing through ten seconds of shaking. Which tower will?

Nobody can stop the ground shaking, but a defense can make the damage smaller. Keegan's defense is a wide, heavy base. Kendra's defense is braces: two sticks taped from corner to corner.

Each tower gets the same test: the same shaking for ten seconds. Let's shake them. Keegan's tower loses its top three blocks. Kendra's tower sways, and every block stays.

Which protects better? The braces: they gave less damage in the same test. Looking at the towers could not tell us that. Only the test did.

So, to find which defense protects better, give both designs the same shaking test. The design with less damage protects better.

Okay, now your turn.

Here's everything we found out about what happens in an earthquake.

First, the ground is the top of Earth's hard rocky outer shell, called the crust. The soil is only a thin layer on top of the rock.

Next, an earthquake starts where rock deep in the crust suddenly slips. The shaking spreads out through the crust as waves, so the ground shakes far from where the rock slipped.

And last, to find which defense protects better, give both designs the same shaking test. The design with less damage protects better.

Okay, now your turn.

Here's Belle at the classroom window on a rainy Monday. Rain pours from a gray cloud, and a puddle spreads across the playground.

On Wednesday the sky is blue, and the puddle is gone. Nobody mopped it up.

On Friday it rains again. Belle wonders whether the same water has come back.

Where did the puddle's water go, and where does rain come from?

To find out, we will look at what falls from clouds, where the water goes, and what the Sun has to do with it.

Okay, so are you ready to find out where the rain comes from?

Here's Miss Hayes's class at the window. Rain falls from a gray cloud onto the playground. Landon says snow fell from a cloud like that one last winter. What do rain and snow have in common?

First, what is a cloud? It looks like cotton balls, but it isn't. A cloud is many tiny drops of water floating in the air.

The tiny drops bump and join into bigger drops. Earth pulls the big drops down, and they fall. That's rain.

And now, in very cold air, the water in the cloud freezes into flakes of ice. They fall. That's snow.

Sleet is small grains of ice, and hail is balls of ice. Both fall from clouds too.

So, here's what we've seen. Water falls from clouds as rain, snow, sleet or hail. Water falling from clouds like this is called precipitation.

Okay, now your turn.

Here's Miss Hayes's class on the hill behind the school, after the rain. Water runs down the hill in little streams. Laura asks where all that rainwater goes.

Rainwater runs downhill. On the hill it runs into a stream, and the stream flows into a river.

The river flows into a lake, or on to the sea.

And now look at the soft soil. Some rainwater soaks into the ground.

Some gathers in low places: a puddle, a pond, a lake.

All of this water is open to the air. So it can evaporate again.

So, here's what we've seen. Fallen water gathers in streams, rivers, lakes, the sea and the ground. Water gathering like this is called collection. It is ready to evaporate again.

Okay, now your turn.

Here's Belle's puddle on the playground after Monday's rain. By Wednesday it's gone, and on Friday it rains again. Landon says the puddle's water is gone for good. Is he right?

No, he isn't. The water evaporated: it went into the air, bit by bit, as water vapor you cannot see.

Moving air carries the water vapor high up, where the air is cold. There it cools and condenses into tiny drops. Many tiny drops together are a cloud.

The drops join into big drops and fall as rain: precipitation. The rain gathers in streams, rivers, lakes, the sea and the ground: collection.

That water is open to the air, so it evaporates again.

So, here's what we've seen. The water cycle is one loop that goes round and round: evaporation, condensation, precipitation, collection, then evaporation again. It has no start and no end.

Okay, now your turn.

Here are two puddles after the rain: one in the sun, one in the shade of the school. By afternoon the sunny one is dry. Landon says the Sun sucked the water up. Is he right?

No, he isn't. Nothing is sucked up, and nothing is lifted. The Sun's light carries energy to the puddle. The water warms up, and warm water evaporates faster.

The Sun's light lands on the sea, lakes, rivers and wet ground too. All that water warms up and evaporates, so there is always water vapor in the air for clouds and rain.

Now imagine the Sun stopped shining. The water would stay cold, and hardly any rain would fall.

So, here's what we've seen. The Sun's light carries energy to the water on Earth. The water warms up and evaporates. So the Sun's energy keeps the water cycle going.

Okay, now your turn.

Here's Miss Hayes's class back from the hill. She asks them to follow one drop of water. Laura picks a drop in the sea. What happens to it next?

To predict the next step, find the drop in the loop. The sea is collection. The next arrow is evaporation, so the drop evaporates.

Now it's water vapor, high up in cold air. The next arrow is condensation, so it condenses into a tiny drop in a cloud.

Now the drop in the cloud has grown big. The next arrow is precipitation, so it falls as rain.

Now it's rainwater on a hill. The next arrow is collection: it runs into a stream, a river and the sea, and evaporates again.

So, to predict a drop's next step, find where the drop is in the loop. Its next step is the next arrow round.

Okay, now your turn.

Here's everything we found out about the water cycle.

Water falls from clouds as rain, snow, sleet or hail. Water falling from clouds like this is called precipitation.

Fallen water gathers in streams, rivers, lakes, the sea and the ground. Water gathering like this is called collection. It is ready to evaporate again.

The water cycle is one loop that goes round and round: evaporation, condensation, precipitation, collection, then evaporation again. It has no start and no end.

The Sun's light carries energy to the water on Earth. The water warms up and evaporates. So the Sun's energy keeps the water cycle going.

And to predict a drop's next step, find where the drop is in the loop. Its next step is the next arrow round.

Okay, now your turn.

Here's Miss Ortiz's class around a globe. Leah gives it a spin, and nearly everything that goes past is blue.

Levi says Earth is nearly all water, so we will never run short of water to drink. But Miss Ortiz says most of that blue is water nobody can drink.

So where is Earth's water, and how does the water in that blue ever reach a river, a tap or a rain cloud?

To find out, we will look at where Earth's water sits, why the little fresh water matters, how the ocean feeds the rain, and how to build the water cycle on a windowsill.

Okay, so are you ready to find out where Earth's water is?

Here's Miss Ortiz's class around a globe. Leah spins it. Nearly everything going past is blue. Levi says Earth is nearly all water, so we'll never run short of water to drink. Is he right?

No, he's not right. Nearly all of that blue is the ocean, and its water has salt in it. Water with salt in it is called salt water. Nobody can drink it.

Suppose all of Earth's water filled 100 squares. 97 squares are salt water in the ocean. 2 squares are fresh water, with no salt in it, frozen in ice caps and glaciers. And only 1 square is fresh water we can reach, nearly all under the ground.

So, here's what we've seen. Nearly all of Earth's water is salt water in the ocean. Most of the fresh water is frozen in ice caps and glaciers, or under the ground.

Okay, now your turn.

Here's Liana's town in July. No rain has fallen for six weeks, so the town has turned off its fountains and asked everyone to use less water. Liana says the ocean is full, so why not use that? Is she right?

No, she's not right. A person who drinks salt water gets sick, and a corn plant watered with salt water dies. People, animals and plants on land need fresh water.

Now, the town's fresh water comes from a reservoir, a big lake built to store a town's water. Rain fills it. This summer almost no rain has fallen, but the town keeps using water, so the reservoir is running short.

So, here's what we've seen. People, animals and plants on land need fresh water. Only a little of Earth's water is fresh water we can reach, and when the rain stops, it runs short.

Okay, now your turn.

Here's Levi's town, with a gray rain cloud over it and rain starting to fall. A small lake sits at the edge of the town. Levi says all of this rain came out of our lake. Is he right?

No, he's not right. The Sun's light carries energy to the water on Earth, so the water warms up and evaporates. The lake evaporates, but so does every river, every puddle, and the whole ocean.

Now, 97 of every 100 squares of Earth's water are in the ocean, so most of the Sun's light that lands on water lands on the ocean. Of every 10 cups of water that go into the air, about 9 come from the ocean.

So, here's what we've seen. Most of the water that goes into the air evaporates from the ocean, because the ocean is where most of the water is.

Okay, now your turn.

Here's the class at the edge of the sea. A wave splashes Liana, and the water tastes salty. A dark cloud comes in, and rain begins to fall. Levi says rain from the ocean should taste salty too. Is he right?

No, he's not right. Here's a dish of sea water left in the sun. By evening the water has evaporated, but a white crust of salt is left behind.

The same happens over the whole ocean. The vapor rising off it has no salt, so the rain that falls on the land is fresh water, and rivers carry it back to the ocean.

So, here's what we've seen. Evaporation takes the water from the ocean and leaves the salt behind, so rain is fresh water. Rivers carry the rain water back to the ocean, so the ocean is connected to all Earth's water.

Okay, now your turn.

Here's Miss Ortiz's class at a sunny window with a glass bowl, a cup, plastic wrap, ice and warm salt water. How can these become an ocean, a sky and rain?

Levi pours the salt water into the bowl: that's the ocean. Leah stands the cup in the middle: that's the land. Liana stretches the wrap over the top and sets the ice on it.

In the sun the water evaporates. Under the cold spot the vapor condenses into drops that drip into the cup. The cup's water is fresh: the salt stayed in the bowl.

So, to build a water cycle model, make an ocean, a cup for the land, a cover for the sky and something cold on top. Then label each part: the water and the drops are a liquid, the vapor is a gas, and the ice is a solid.

Okay, now your turn.

Here's everything we found out about where Earth's water is.

Nearly all of Earth's water is salt water in the ocean. Most of the fresh water is frozen in ice caps and glaciers, or under the ground.

People, animals and plants on land need fresh water. Only a little of Earth's water is fresh water we can reach, and when the rain stops, it runs short.

Most of the water that goes into the air evaporates from the ocean, because the ocean is where most of the water is.

Evaporation takes the water from the ocean and leaves the salt behind, so rain is fresh water. Rivers carry the rain water back to the ocean, so the ocean is connected to all Earth's water.

To build a water cycle model, make an ocean, a cup for the land, a cover for the sky and something cold on top. Then label each part: the water and the drops are a liquid, the vapor is a gas, and the ice is a solid.

Okay, now your turn.

Here's Bianca walking to school in Austin, Texas, one January morning, in a T-shirt. The thermometer on the porch reads 68 degrees Fahrenheit.

That night, the news shows Duluth, Minnesota, under a snowstorm: 22 degrees Fahrenheit, and cars buried to their windows.

So is Duluth a cold place, or did it just have a cold day, and how could anyone tell?

To find out, we will look at what a place is usually like, how to put years of weather records into a bar graph, how to compare two places, and how to read a place's usual weather off its records.

Okay, so are you ready to find out what a place's weather is usually like?

Here's Miss Jensen's class in Austin, Texas, on a video call with their partner class in Duluth, Minnesota, one January afternoon.

Behind the Duluth class, snow is falling. Their thermometer reads 22 degrees Fahrenheit, and Austin's reads 68.

Lincoln says Duluth is a cold place. Logan says that's just today's weather.

Logan is right about today. The weather is what the sky and the air are like at a place on one day.

But here is the Duluth class's weather table for the last 5 Januaries. Every January had 8 or more snowy days.

The same cold, snowy weather came back every winter. So Lincoln is right too, about what Duluth is usually like.

The weather a place usually has, year after year, is called its climate.

Duluth's climate has cold, snowy winters. Austin's climate has mild winters, cool with almost no snow, and hot summers.

Okay, now your turn.

Here's Miss Jensen's board with six sentences. Ask each: one day or a few days, or year after year?

It rained in Austin yesterday. Yesterday is one day, so it tells the weather.

Austin has hot summers most years. Most years means year after year, so it tells the climate.

A storm is coming to Duluth this afternoon. That is one day, so it tells the weather.

Duluth's winters are long and snowy. That is every winter, so it tells the climate.

Austin has been cold all this week. A week is a few days, so it still tells the weather.

Last January, Duluth had 11 snowy days. One month of one year still tells the weather.

So, a sentence about one day, or a few days, tells the weather. A sentence about what a place is usually like, year after year, tells the climate.

Okay, now your turn.

Here's Bianca with the Duluth class's table of snowy days in 5 Januaries. She wants all 5 years in one picture, so she will make a bar graph.

First, she writes the title at the top: snowy days each January, Duluth, Minnesota.

Up the side, she writes the label, snowy days, because that is what the numbers count. The most in any January was 11, so she writes every number from 0 to 12.

Along the bottom go the 5 years. Under them she writes the label, year, because each bar will stand for a year.

So, a bar graph also needs two labels: one up the side saying what the numbers count, and one along the bottom saying what each bar stands for.

Okay, now your turn.

Here's Bianca's graph with its title, both labels and every number from 0 to 12, and no bars yet.

Before any bar, she rules a line right across at every number. Then each bar's top will land on a line.

The table says 2022 had 9 snowy days, so the 2022 bar goes up to the 9 line.

The 2023 bar goes up to 11. Then 2024 goes up to 8, 2025 to 10, and 2026 to 9.

The tallest bar is 2023. That is not the snowiest day: each bar stands for a whole January, so 2023 is the January with the most snowy days.

So, before you draw any bar, rule a line right across at every number. Then draw one bar for each name, up to its number.

Okay, now your turn.

Here's Lincoln with two bar graphs: snowy days each January in Duluth and Austin. Which town had more?

On his first try, Austin's numbers go only 0 to 2, so its one bar reaches half-way up.

But that bar means 1 snowy day, and Duluth's mean 8 to 11. With different numbers up the side, the bars cannot be compared by eye.

So Lincoln redraws Austin's graph with 0 to 12 up the side, like Duluth's.

Now Austin's one bar is tiny, and 4 years have none. Every Duluth bar is taller, so Duluth had more.

Year by year works too: in 2023, Duluth had 11 and Austin had 1. 11 take away 1 is 10 more.

So, to compare two sets of results, draw them with the same numbers up the side. Then compare the bars: the set with the taller bars shows more.

Okay, now your turn.

Here's Bianca with two graphs: snowy days each January in Duluth and in Austin. Miss Jensen asks for a sentence saying each town's winter climate.

Duluth's numbers are 9, 11, 8, 10 and 9: every January had 8 or more snowy days.

Snowy Januaries came every year, so snowy Januaries are Duluth's usual weather. Bianca writes: Duluth's winter climate is cold and snowy.

Austin's graph shows 1 or fewer snowy days every January, so Bianca writes: Austin's winter climate is mild, with almost no snow.

So, to work out a place's climate, look at its records from several years, and find the weather that came every year. That usual weather is the climate.

Okay, now your turn.

Here's Austin one January afternoon: the thermometer reads 28 degrees Fahrenheit, and Lincoln says Austin has a cold winter climate.

Here is the class weather table for that January as a graph. Each line is worth 2 degrees Fahrenheit; every fifth line has its number.

7 of the 8 afternoons were 58 degrees Fahrenheit or warmer. The 28 does not fit the rest.

A result that does not fit is checked first. The thermometer hung in the shade, and the news reported a cold snap, so the 28 was real: one odd day.

No, Lincoln is not right. One cold day does not change the usual pattern, so Austin's winter climate is still mild.

So, a result that does not fit the rest is checked, then set aside. One odd day does not change the climate, because the climate is the usual pattern.

Okay, now your turn.

Here's everything we found out about weather and climate.

The weather is what the sky and the air are like at a place on one day. The weather a place usually has, year after year, is its climate.

Next, a sentence about one day, or a few days, tells the weather. A sentence about what a place is usually like, year after year, tells the climate.

Then, a bar graph also needs two labels: one up the side saying what the numbers count, and one along the bottom saying what each bar stands for.

Before you draw any bar, rule a line right across at every number. Then draw one bar for each name, up to its number.

To compare two sets of results, draw them with the same numbers up the side. Then the taller bars show more.

To work out a place's climate, find the weather that came every year in its records.

One odd day does not change the climate, because the climate is the usual pattern.

Okay, now your turn.

Here's Miss Nakamura's class, walking to the sea on a windy day. Sand blows along the beach, the lake is rough with waves, and the reeds bend over.

Nobody is touching the water. So what is making the waves?

And the sand did not pile itself up into that tall hill. Something piled it there.

To find out, we will look at how to read a map of the land, how the land, the water, the air and the living things change one another, and how to spot which one is acting on which.

Okay, so are you ready to find out how Earth's parts act on one another?

Here's Miss Nakamura's class, planning a walk to the sea. Louis holds the map. Luna asks: where is the water?

A map shows the land from straight above. Look at the hills: the brown shapes run in a long line along the top.

The box along the bottom is called the legend. It says what each color and shape stands for: blue means water, brown means hills, green means forest, and dark squares mean a town.

The shape tells you which water it is: the big blue area at the edge is the sea, the small shape with land all round it is a lake, and the thin line is the river.

So, a map shows the land from straight above. The legend says what each color and shape stands for, so you can find each thing on the map and say where it sits.

Okay, now your turn.

Here's Miss Nakamura's class by the river. The path has fallen in, and part of the bank is gone. Luna asks: what took the path away?

Everything here belongs to one of Earth's four big parts: the land, the water, the air, and the living things.

The river's water carried the bank's soil away. The water acted on the land.

On the lake, the wind pushed the water into waves: the air acted on the water. On the hill, tree roots held the soil together: the living things acted on the land. In the field, rain made the grass grow: the water acted on the living things.

Earth's four big parts are the land, the water, the air and the living things. Each part acts on the others and changes them. When one part acts on another and changes it, we call that an interaction.

Okay, now your turn.

Here's Miss Nakamura's class at the beach, beside a tall pile of sand with grass on top. Josie asks: who piled this sand up?

The wind blew sand along the beach into a pile. Which part is doing the acting? The wind, and the wind is air. Which part is being changed? The sand, and the sand is land. So the air acts on the land.

Now grass grows on the pile, and its roots hold the sand. The grass is a living thing, so the living things act on the land.

A hawk catching a mouse? The hawk and the mouse are both living things, so that is inside one part, not one part acting on another.

To spot the interaction, ask two questions. Which part is doing the acting? Which part is being changed? Then say it: the first part acts on the second.

Okay, now your turn.

Here's the class. Louis says the land acted on the air. Josie says the air acted on the land. Who is right?

Here's a beaver's dam across a stream. The beaver is a living thing, and the stream is water: the living things act on the water.

Here's a river meeting the sea. It drops its sand, and new flat land grows. The river is water, so the water acts on the land.

Here's a flooded field. Flood water is water, and crops are living things: the water acts on the living things.

Here's the sand again. Ask the two questions that spot the interaction. Which part is doing the acting, and which is being changed? The wind acts, and the sand is changed. So the air acts on the land, not the land on the air. Say the acting part first: Josie was right.

Okay, now your turn.

Here's everything we found out about how Earth's parts act on one another.

First, a map shows the land from straight above. The legend says what each color and shape stands for, so you can find each thing on the map and say where it sits.

Next, Earth's four big parts are the land, the water, the air and the living things. Each part acts on the others and changes them. When one part acts on another and changes it, we call that an interaction.

And last, to spot the interaction, ask two questions. Which part is doing the acting? Which part is being changed? Then say it: the first part acts on the second.

Okay, now your turn.

Here's Miss Okoro's class on a stormy afternoon. The lights go out. For one minute the room is dark, and then the lights come back on.

Maddox asks where the electricity comes from. Miss Okoro says some of it comes from the wind, some from a river, some from sunlight, and some from plants.

But how can moving air, or a river, or sunlight, or a log, end up as light in a classroom lamp?

To find out, we will look at the tall towers with blades on a hill, a wall across a river, dark panels on a roof, and a log burning in a stove.

Okay, so are you ready to find out where the electricity comes from?

Here's Maddox in the car in west Texas. On a hill stands a row of tall white towers, each with three long blades, turning slowly. His dad says they make electricity. But how can moving air end up as electricity?

Here is a pinwheel. Moving air pushes on the blades of a wheel, so the wheel turns. The wind pushes these long blades the same way.

The turning blades turn a machine inside the top of the tower, and the machine makes electricity.

The electricity carries energy along wires from the tower to the homes. On a still day, no moving air pushes the blades, so the machine makes no electricity.

So, the wind pushes the blades of a wind turbine round, and the turning blades turn a machine that makes electricity. A thing in nature that people get energy from is called an energy resource.

Okay, now your turn.

Here's Ayesha on top of a dam in Tennessee. A wide lake sits on one side. Far below on the other side, water rushes out. Her mom says the dam makes electricity. But how can a wall do that?

Here is a mill's water wheel. Moving water pushes the blades of a wheel, so the wheel turns.

Inside the dam, water from the high lake falls through a big pipe and pushes the blades of a wheel round.

The turning wheel turns a machine that makes electricity, and the electricity carries energy along wires to the city. When the pipe is shut, no water moves, so the wheel stays still.

So, moving water pushes the blades of a wheel inside a dam round, and the turning wheel turns a machine that makes electricity. The river keeps flowing, so nature keeps giving this energy resource.

Okay, now your turn.

Here's Malia on her front steps one sunny morning. Across the street, the neighbor's roof has four dark panels, and the neighbor says they run the lights. But the panels never move. How can they make electricity?

Here is a face in the Sun. The Sun's light carries energy to whatever it falls on, so the face warms up.

Sunlight falls on the dark panel. The panel is a machine that makes electricity when light falls on it. Nothing inside it turns.

The electricity carries energy along a wire into the house, and the lamp lights up. At night, no sunlight falls on the panel, so it makes no electricity.

So, when sunlight falls on a solar panel, the panel makes electricity, and the electricity carries energy along wires into the house. At night no sunlight falls on the panel, so the panel makes no electricity.

Okay, now your turn.

Here's Miss Okoro's class in a cabin, eating corn bread. She lights two logs and says logs and corn are energy resources. Malia says a log cannot be.

Here is corn. A plant does not eat: it makes its own food, using sunlight.

The log burns, and its heat carries energy to the room. A cold log is not moving and not hot. But everything has some energy, and when it burns, its heat carries energy away. Some big buildings burn wood chips: the heat boils water, and steam pushes a wheel round.

The corn bread has energy too. When Ayesha eats it, that energy moves to her body.

So, plants are an energy resource. Wood from a tree burns, and its heat carries energy to the room. Food from a plant has energy, and that energy moves to your body when you eat it.

Okay, now your turn.

Here's everything we found out about energy from wind, water, sunlight and plants.

First, the wind pushes the blades of a wind turbine round, and the turning blades turn a machine that makes electricity. A thing in nature that people get energy from is called an energy resource.

Next, moving water pushes the blades of a wheel inside a dam round, and the turning wheel turns a machine that makes electricity.

Then, when sunlight falls on a solar panel, the panel makes electricity, and the electricity carries energy along wires into the house. At night no sunlight falls on the panel, so the panel makes no electricity.

And last, plants are an energy resource. Wood from a tree burns, and its heat carries energy to the room. Food from a plant has energy, and that energy moves to your body when you eat it.

The wind blows again, the river keeps flowing, the Sun rises, and new plants grow, so nature keeps giving all four.

Okay, now your turn.

Here's Maria and her family on a car trip across Wyoming. Beside the highway, a train rolls past: a hundred open cars heaped with black rocks.

Farther on, big metal pumps nod up and down in a field.

Back home, her mom lights the stove: a click, and a ring of blue flames.

Her dad says all three come from under the ground. But what are they, and how did they get down there?

To find out, we will look at a black rock that burns, a thick dark oil from deep rock, and a gas that burns with a blue flame.

Okay, so are you ready to find out what we dig, pump and pipe from under the ground?

Here's Maria at her grandpa's cabin. He tips black lumps into the stove, and they glow red. Maria asks: how can a rock burn?

Those black lumps are coal. A log burns, and coal burns. A thing people burn to get heat is called a fuel.

Now let's go back a very long time, to a swamp full of plants. The plants die, fall into the water, and mud covers them.

More layers pile on top and press the dead plants for a very long time, until they turn into coal.

People dig the coal up and burn it in a big building called a power plant, to make electricity.

So, coal is a black rock that burns, formed from plants of long-ago swamps, buried and pressed for a very long time. People dig coal up and burn it in power plants to make electricity.

Okay, now your turn.

Here's Micah at a gas station. Across the road, a big pump nods in a field. Micah asks: is there a lake of oil under it?

No. Oil is a thick dark liquid, and it sits in the tiny spaces of deep rock, like water in a sponge.

Imagine a sea a very long time ago, full of tiny living things. They die and sink, mud buries them, and the layers press them for a very long time, until they turn into oil.

A well pumps the oil up, a factory makes gasoline from it, and cars burn the gasoline.

So, oil is a thick dark liquid that burns, formed from tiny living things of long-ago seas, buried and pressed for a very long time. People pump oil up from deep rock, make gasoline from it, and burn the gasoline in car engines.

Okay, now your turn.

Here's Joy making pancakes with her dad. He turns the stove knob, and blue flames pop up. Joy asks: is that the same gas as the car's?

No, it is not. The car burns gasoline, made from oil. The stove burns natural gas, a gas you cannot see, piped from deep underground.

Tiny sea living things were buried and pressed for a very long time. Some turned into oil, and some into natural gas, trapped in the rock above the oil.

A well brings the gas up, and pipes carry it to stoves, furnaces and power plants.

So, natural gas is a gas that burns, trapped in the tiny spaces of deep rock, formed with the oil from the same tiny sea living things. People pipe it to stoves, furnaces and power plants and burn it for heat and to make electricity.

Okay, now your turn.

Here's Miss Petrov's class with the three fuels from under the ground: coal, oil and natural gas. Micah asks: does the ground make new ones every day, the way the wind blows every day?

No, it does not. The wind blows again every day, and the Sun rises again every morning, so nature keeps giving them.

Coal, oil and natural gas are not like that. The swamps and seas they came from were a very long time ago.

So, coal, oil and natural gas came from living things of a very long time ago. Nature does not make more in our lifetimes.

Okay, now your turn.

Here's everything we found out about fuels from under the ground.

First, a thing people burn to get heat is called a fuel. Coal is a black rock that burns, formed from plants of long-ago swamps, buried and pressed for a very long time. People dig coal up and burn it in power plants to make electricity.

Next, oil is a thick dark liquid that burns, formed from tiny living things of long-ago seas, buried and pressed for a very long time. People pump oil up from deep rock, make gasoline from it, and burn the gasoline in car engines.

Then, natural gas is a gas that burns, trapped in the tiny spaces of deep rock, formed with the oil from the same tiny sea living things. People pipe it to stoves, furnaces and power plants and burn it for heat and to make electricity.

And coal, oil and natural gas came from living things of a very long time ago. Nature does not make more in our lifetimes.

Okay, now your turn.

Here's Monica at home on a cold evening in West Virginia. The lights are on, the furnace hums, and her mom's car sits in the driveway with a full tank.

Her mom says that all of it took energy from somewhere: the lights, the heat, the car.

Monica wonders: will there always be more? Or does some of it get used up?

To find out, we will look at which energy resources nature makes more of, which ones it does not, and the mark that using each one leaves.

Okay, so are you ready to find out which energy resources nature can replace?

Here's Nathan's class on a school trip to a wind farm in Texas. All afternoon the row of tall turbines turns. Nathan asks: if the turbines use the wind all day, is there less wind tomorrow?

No. Tomorrow the wind blows again, as strong as ever. Nature makes more wind by tomorrow.

And now the solar panels on a school roof take in sunlight all day. Tomorrow the Sun shines again.

And a river turns the wheel in a dam all year. Rain fills the river again.

And logs are burned in a stove. In the forest, new trees grow big in some years, well inside a lifetime.

So, here's what we've seen. A renewable resource is one nature makes more of in our lifetimes, about as fast as people use it. Wind, moving water, sunlight and plants are renewable.

Okay, now your turn.

Here's Monica with her grandpa, who worked in a coal mine in West Virginia. The mine closed: every bit of coal there was dug out. Monica asks: won't more coal grow back?

No. That coal formed from plants of long-ago swamps, buried and pressed for millions of years. Nature makes new coal just as slowly.

Oil and natural gas formed from tiny sea living things, the same slow way. People call all three fossil fuels.

A lifetime is about eighty years. Millions of years is far longer, so nature cannot keep up.

There is still a lot under the ground, but every ton dug up is one fewer.

So, a nonrenewable resource is one nature takes far too long to replace, so once it is used up it is gone. Coal, oil and natural gas are nonrenewable.

Okay, now your turn.

Here's Miss Quintero's class. The seven energy resources are written along the top of the board, with two empty boxes under them. Which question sorts them?

One question sorts them all: does nature make more of it in our lifetimes?

Nature makes more wind by tomorrow, so wind goes in the yes box. Nature takes millions of years to make more coal, so coal goes in the no box.

Sunlight goes in yes, and oil goes in no. Moving water goes in yes, and natural gas goes in no.

A tree takes some years to grow big, and some years are inside our lifetimes. So plants go in yes.

So, to sort an energy resource, ask: does nature make more of it in our lifetimes? If yes, the resource is renewable. If no, the resource is nonrenewable.

Okay, now your turn.

Here's Jake in Miss Quintero's class, holding an empty glass bottle for the recycling bin. He says glass can be recycled, so the bottle is a renewable resource. Is he right?

No, he's not right. A bottle can be recycled into a new bottle. But recycling is something people do. It is not nature making more.

Now think of a lamp plugged into the wall. Electricity carries energy along the wires to the lamp.

The electricity came from a power plant, and the power plant got its energy from a resource, like coal or wind. So electricity itself is not a resource.

So, a recycled thing is not renewable: recycling is something people do, not nature making more. Electricity is not an energy resource: it carries energy from a resource.

Okay, now your turn.

Here's Jake's class making a poster of the mark each energy resource leaves. Jake says wind turbines leave no mark. Is he right?

No. A wind farm is a row of tall turbines across a field that was only grass. That is a mark on the land.

A power plant burns coal, and smoke goes into the air. The coal came from a mine, a big hole in the ground.

Burning gasoline, natural gas or logs puts smoke, or a gas you cannot see, into the air.

A dam holds a river back, so the valley above it becomes a lake. And solar panels cover a field.

So, here's what we've seen. Using any energy resource leaves a mark on the land, the air or the water: smoke in the air, a mine or a flooded valley, or a field covered with turbines or solar panels.

Okay, now your turn.

Here's Miss Quintero's class. The town needs a new power plant, and she shows two drawings: a wind farm on the hill, or a plant that burns natural gas. Which would you choose?

Wind has a good side: no smoke, and nature makes more wind by tomorrow. But the turbines turn only when the wind blows.

Natural gas has a good side too: the plant runs day and night. But burning it puts a gas into the air, and nature cannot keep up.

A good side of using a resource is called an advantage. A bad side is called a disadvantage.

Every resource has both. The town asks which matters more: electricity on still nights, or clear air.

So, to weigh up an energy resource, name one advantage of using it and one disadvantage. Every energy resource has both.

Okay, now your turn.

Here's everything we found out about which energy resources nature can replace.

A renewable resource is one nature makes more of in our lifetimes, about as fast as people use it.

A nonrenewable resource is one nature takes far too long to replace, so once it is used up it is gone.

To sort an energy resource, ask: does nature make more of it in our lifetimes? If yes, the resource is renewable. If no, the resource is nonrenewable.

A recycled thing is not renewable: recycling is something people do, not nature making more. Electricity is not an energy resource: it carries energy from a resource.

Using any energy resource leaves a mark on the land, the air or the water: smoke in the air, a mine or a flooded valley, or a field covered with turbines or solar panels.

To weigh up an energy resource, name one advantage of using it and one disadvantage. Every energy resource has both.

Okay, now your turn.

Here's Paige at the school bus stop at 7 in the morning in May. The Sun is already up, and the birds are singing.

Now it's December, the same bus stop, the same 7 in the morning. The sky is still dark, and the streetlight is still on.

Where did the morning daylight go? And will it come back?

To find out, we will look at where the Sun goes across the sky each day, how the daylight grows and shrinks through the year, and how to read a season from the records.

Okay, so are you ready to find out where the daylight went?

Here's Miss Rasmussen's class at morning recess. Wade points at the Sun, low over the parking lot.

Where will the Sun be at lunchtime?

Let's watch the whole day.

Early in the morning, the Sun comes up over the parking lot. That side is the east.

Through the morning, the Sun seems to get higher. Around midday it's at its highest, over the gym, but not straight overhead.

Through the afternoon it seems to get lower, and at the end of the day it goes down behind the trees. That side is the west.

The curve the Sun seems to follow across the sky each day is called the Sun's path.

So, every day, the Sun seems to move across the sky on a curved path. It comes up in the east, is highest around midday, and goes down in the west.

Okay, now your turn.

Here's Oliver's soccer practice ending at 6. In June, the Sun is still up.

But in November, the field lights are on and the sky is already dark. Where did the daylight go?

Here's the Sun's path in June. It comes up early, goes high above the gym, and goes down late.

The June path is high and long.

In November, the Sun comes up late, stays low, and goes down early.

The November path is low and short.

The class counted the daylight hours each month and drew a graph.

From December to June the bars grow taller a little each month.

After June the daylight stops growing. From July to December they grow shorter a little each month.

So, the number of daylight hours changes a little each month. The days grow longer from winter to summer, and shorter from summer to winter.

Okay, now your turn.

Here's Paige with a bar graph from her cousin's class in Portland, Maine. It shows the afternoon temperature each month for a year.

Miss Rasmussen asks: can you find Portland's winter and summer on the graph?

Look at the bars. The shortest bars are January and February, and those cold months are winter.

The tallest bars are July and August. Those warm months are summer.

Between winter and summer, the bars grow taller each month. That's spring.

And between summer and winter, the bars grow shorter each month. That's fall.

So, to read a season from the records, look at the bars. The shortest bars are winter, and the tallest are summer.

In spring the bars grow taller each month; in fall they grow shorter.

Okay, now your turn.

Here's Miss Rasmussen's class at the end of April with four months of records. Oliver asks: how many hours will May have?

Here are the records as bars: January 10 hours, February 11, March 12, April 13. Each month has one more hour than the one before.

That happens again and again in the same way, so it's a pattern.

Now carry the pattern on one more step. April had 13 hours, so May should have 14.

In May the class counts the daylight: 14 hours. The prediction was right.

After June the daylight stops growing. From July the records grow shorter each month, so the next month is shorter still.

So, to predict the next step, find the pattern in the records so far, and carry it on one more step. If the daylight has grown longer each month, next month will be longer still.

Okay, now your turn.

Here's everything we found out about the Sun's path and the seasons.

First, every day, the Sun seems to move across the sky on a curved path. It comes up in the east, is highest around midday, and goes down in the west.

Next, the number of daylight hours changes a little each month. The days grow longer from winter to summer, and shorter from summer to winter.

Then, to read a season from the records, look at the bars. The shortest bars are winter, and the tallest are summer. In spring the bars grow taller each month; in fall they grow shorter.

And last, to predict the next step, find the pattern in the records so far, and carry it on one more step. If the daylight has grown longer each month, next month will be longer still.

Okay, now your turn.

Here's Paul at his bedroom window in Dallas, early in the morning. The Sun comes up over the houses across the street.

By dinner time, the Sun goes down behind the trees on the other side of the street. And that night, the stars above the house seem to move too, slowly, all night long.

Does the whole sky really travel around us? Or is something else moving, something we are standing on?

To find out, we will look at how Earth spins, how it travels around the Sun, and what the stars do through the night and through the seasons.

Okay, so are you ready to find out what is really moving?

Here's Miss Santos spinning the classroom globe. A red sticker marks Andre's town. Andre asks: how long does the real Earth take to spin around once?

Here is Earth from far above the North Pole. The Sun is at the left, so the half facing the Sun is lit, and the other half is dark.

Earth spins this way, all the time. It spins so smoothly and steadily that nobody can feel it.

Now look at the red dot. After 6 hours, Earth has made a quarter turn. After 24 hours, it has spun all the way around, and the dot is back where it started.

When Earth has spun all the way around once, we call that time one day.

So, Earth spins all the way around once in about 24 hours. One spin is one day.

Okay, now your turn.

Here's the class singing to Andre on his tenth birthday. Miss Santos says Earth has done something big since his last birthday. Phoebe asks: what has Earth done?

Earth travels around the Sun along a path called an orbit. Here is Earth on its orbit on Andre's birthday.

Earth keeps traveling along its orbit. After 6 months, it has gone halfway around. After 12 months, it is back at the birthday place.

So since Andre's last birthday, Earth has traveled once around the Sun. That trip takes about 365 days, and we call that time one year.

Earth spins around once in a day. It travels around the Sun once in a year. Those are two different things.

So, Earth takes about 365 days to travel once around the Sun. One trip around the Sun is one year.

Okay, now your turn.

Here's Phoebe on her grandmother's farm porch in Kansas at 9 PM. Seven bright stars shine above the barn, shaped like a big spoon.

At midnight the seven stars are higher and farther to the right. Did they change their shape?

No, they did not. Lines joining the stars show the same shape at midnight as at 9 PM. The whole group moved together.

A group of bright stars that makes a shape you can recognize is called a star pattern. People who study the stars call it a constellation.

Here's another star pattern, five stars in a W. At midnight the W is in a new place, still the same W. Every pattern moves across the sky together, keeping its shape.

So, the stars in a star pattern keep the same shape all night. The whole pattern moves across the sky together.

Okay, now your turn.

Here's Paul with his dad in their Dallas backyard on a cold January evening. Above the fence shine seven bright stars, three in a short straight row. His dad says that star pattern is called Orion.

Every January evening, Orion is there. But in July, Paul looks up after dinner, and Orion is gone. Other patterns are up, like a big triangle of bright stars.

Where did Orion go? It is still there. In July, Orion is in the sky in the daytime, and the Sun's light hides it.

Next January, Orion is back in the evening sky, and the triangle is gone. The Big Dipper is different: it is in the evening sky all year.

So, different star patterns are in the evening sky in different seasons. A pattern like Orion is in the evening sky in winter, gone in summer, and back next winter.

Okay, now your turn.

Here's Andre in the back seat of the car on the highway. Outside his window, the trees seem to slide past. But the trees stand still, so it is the car that is moving.

Every day the Sun comes up in the east and goes down in the west. At night the Moon and the star patterns seem to move across the sky the same way, together.

Andre asks: is something else really moving, like the car? Yes. Earth spins around once a day, with Andre, the car and the whole of Texas on it.

Because Earth spins, the Sun, the Moon and the stars all seem to move across the sky, together. Only one thing is turning: Earth.

Earth spins, so the Sun, the Moon and the stars all seem to move across the sky. It is Earth that is turning, not the sky.

Okay, now your turn.

Here's everything we found out about the turning Earth and the stars.

First, Earth spins all the way around once in about 24 hours. One spin is one day.

Next, Earth takes about 365 days to travel once around the Sun. One trip around the Sun is one year.

Then, the stars in a star pattern keep the same shape all night. The whole pattern moves across the sky together.

Also, different star patterns are in the evening sky in different seasons. A pattern like Orion is in the evening sky in winter, gone in summer, and back next winter.

And last, Earth spins, so the Sun, the Moon and the stars all seem to move across the sky. It is Earth that is turning, not the sky.

Okay, now your turn.

Here's Ramon in the back seat, on the drive home from his grandma's house at night. Out of the window, the Moon is a thin curved sliver, low in the sky.

Two weeks later, it's the same drive and the same window. But now the Moon is a whole bright circle.

What happened to the Moon in those two weeks? And what will it look like next week?

To find out, we will look at the shapes the Moon shows us, the order they come in, and what makes them change.

Okay, so are you ready to find out why the Moon's shape seems to change?

Here's Piper and Ramon in the yard at bedtime. The Moon is a whole bright circle, and Piper draws it in her notebook.

She draws it every clear night. After a week, her drawing is half of a circle, and after two weeks, there is nothing to draw.

Ramon asks: did a piece of the Moon break off? No, it didn't. Sunlight lands on the Moon and lights it up.

Some nights the whole side we see is lit. Other nights only a thin sliver is lit, and the rest is there in the dark.

Here is the whole month. The lit shape gets smaller each night, down to nothing, then bigger again, back to a whole circle.

So, the Moon's lit shape, seen from Earth, changes a little each night and comes back round in about a month. The Moon itself stays a whole ball.

Okay, now your turn.

Here's Miss Tanaka's class with eight pictures of the Moon from one month. Riley says: I saw that one from the car! But which one does she mean? Each shape needs a name.

Here is the Moon when the whole circle is lit. We call this shape a full Moon.

And now one side is lit, with a straight edge down the middle. We call this a half Moon. It can be lit on the right or on the left.

And now only a thin curved sliver is lit. We call this a crescent Moon.

And now we can't see the Moon at all. We call this a new Moon.

So, a full Moon is a whole lit circle. A half Moon is lit on one side. A crescent Moon is a thin curved sliver. At a new Moon, we cannot see the Moon.

Okay, now your turn.

Here's Ramon with four pictures of the Moon for a poster. He dropped them, so they're mixed up. Which night came first?

Let's start at the new Moon. Night after night, the lit part gets bigger: a crescent Moon, a half Moon, more than half, a full Moon.

Look at which side is lit. While the lit part is getting bigger, it's on the right.

After the full Moon, the lit part gets smaller, back to a new Moon. Now the lit part is on the left.

So Ramon's pictures go: the new Moon first, then the crescent lit on the right, then the half, then the full Moon.

Here's the pattern. From new Moon to full Moon, the lit part gets bigger each night and is on the right. From full Moon to new Moon, it gets smaller and is on the left.

Okay, now your turn.

Here's Riley in her yard. Tonight the Moon is full, and the class night walk is in one week. Will the Moon be full for the walk?

No, it won't. The Moon's shapes take about a month to come back round, and a month is about four weeks. So the shapes we named come about a week apart.

Start at a new Moon. One week later, we see a half Moon. One week after that, we see a full Moon. Then a half Moon comes, and then a new Moon.

So one week after Riley's full Moon, the Moon is a half Moon. And two weeks after it, the Moon is a new Moon.

So, new Moon, half Moon, full Moon and half Moon come about a week apart. So one week after a full Moon, we see a half Moon.

Okay, now your turn.

Here's Miss Tanaka's class with the blinds down. Riley asks: does Earth's shadow cover part of the Moon? No, it doesn't. Let's see what does.

The Moon makes no light of its own: sunlight lands on it, and it is lit up. The Sun lights one half of the Moon. The other half is dark.

Now look from far above. The Moon travels around Earth, and at every place on its path, the half facing the Sun is lit.

From Earth, we see that lit half from different sides. When the lit half faces us, we see a full Moon. When it faces away, we see a new Moon. Half way, we see a half Moon.

So, the Sun lights one half of the Moon. As the Moon travels around Earth, we see that lit half from different sides, so the lit shape we see changes.

Okay, now your turn.

Here's everything we found out about the Moon's changing shape.

First, the Moon's lit shape, seen from Earth, changes a little each night and comes back round in about a month. The Moon itself stays a whole ball.

A full Moon is a whole lit circle. A half Moon is lit on one side. A crescent Moon is a thin curved sliver. At a new Moon, we cannot see the Moon.

From new Moon to full Moon, the lit part gets bigger each night and is on the right. From full Moon to new Moon, it gets smaller and is on the left.

New Moon, half Moon, full Moon and half Moon come about a week apart. So one week after a full Moon, we see a half Moon.

And last, the Sun lights one half of the Moon. As the Moon travels around Earth, we see that lit half from different sides, so the lit shape we see changes.

Okay, now your turn.

Here's Miss Underwood's class at field day.

Roman has just won the race. His chest goes up and down, and his heart thumps.

Dean sees a ball flying his way, and his hands are there to catch it.

By the fence, in a dry corner nobody waters, a prickly plant is green.

What is going on inside Roman, and how did Dean's hands know where to go? And how does that plant live with no water?

To find out, we will look at the heart, the lungs and the stomach, plants in dry places, and how eyes, brain and hands work together.

Okay, so are you ready to find out what the parts inside living things do?

Here's Roman at the doctor's. She presses a stethoscope to his chest. Thump, thump. What's in there?

Under his ribs sit his heart, his two lungs and stomach.

The heart is a lump of muscle the size of his fist. It squeezes again and again; each squeeze pushes blood along tubes round him. A thing that pushes liquid along is called a pump: the heart pumps blood.

Next come the two lungs, one on each side. When he breathes in, air fills both: the lungs take in air.

Lower down sits the stomach, a stretchy bag. It squeezes his breakfast to a thick soup, and the food moves on: it mashes up food.

So, here's what we've seen. Each part inside the body has its own job: the heart pumps blood all round the body, the lungs take in air, and the stomach mashes up food.

Okay, now your turn.

Here's Victor and his dad in the Arizona desert. No rain has fallen for three months. But this cactus and mesquite tree are alive. How are they alive?

A plant's roots take in water from the soil. The top soil here is dry, but far down it is wet, and the mesquite's roots reach it.

Victor's tomato had short roots. They reached only dry soil, so it died.

Next comes the cactus and its thick, fat stem. When rain comes, the stem fills with water and stores it.

And these sharp points, its spines, are its leaves: thin, so little water dries out, and sharp, so animals keep away.

So, here's the pattern. In a tough place, a plant part with the right shape helps the plant survive there: deep roots reach water far down, a thick stem stores water, and thin spines keep water in.

Okay, now your turn.

Here's Dean on the path by the park. A bike bell rings behind him, and he steps onto the grass. His ears heard the bell, but ears can't move feet. What happened in between?

An animal senses something, then it responds. What Dean's ears heard went to his brain. His brain decided: step aside. Then his feet moved.

Everything your eyes see and your ears hear goes to your brain. It decides what to do, and the body acts.

Now let's look at Victor. His nose smells cookies, his brain decides to look, and his legs walk to the kitchen.

And a deer hears a twig snap, its brain decides to run, and its legs run.

So, here's what we've seen. When an animal senses something, what it sensed goes to its brain. The brain decides what to do. Then the body acts: sense, brain, action.

Okay, now your turn.

Here's everything we found out about parts and their jobs, inside animals and plants.

First, each part inside the body has its own job: the heart pumps blood all round the body, the lungs take in air, and the stomach mashes up food.

Next, in a tough place, a plant part with the right shape helps the plant survive there: deep roots reach water far down, a thick stem stores water, and thin spines keep water in.

And last, when an animal senses something, what it sensed goes to its brain. The brain decides what to do. Then the body acts: sense, brain, action.

Okay, now your turn.

Here's Miss Valdez's class eating lunch on the school field. Sally bites an apple, a sparrow pecks at her crumbs, and the grass is thick and green under them all.

Everything out here is eating, except the grass. The grass never eats a thing, and yet it grows all summer long.

So what is the grass living on? And the apple in Sally's hand, where did the energy in it come from?

To find out, we will look at how a plant makes its own food, why an animal cannot, and where the energy in your lunch came from.

Okay, so are you ready to find out how plants make their own food?

Here's Sally watering the class sunflower. Nobody feeds it, she says. Where does its food come from?

A plant does not eat. It makes its own food in its leaves.

The Sun's light carries energy to the leaf.

The roots take in water from the soil.

And the leaf takes in a gas from the air: carbon dioxide.

With that energy, the leaf makes sugar from the water and the carbon dioxide. Sugar is its food.

In a dark closet, no light lands on the leaves, so no sugar is made, and the plant turns pale. Neither the soil nor the light is its food: the sugar is.

So, a plant makes its own food in its leaves. The leaf uses water from the soil, carbon dioxide from the air, and the energy the Sun's light carries, to make sugar. The sugar is the plant's food.

Okay, now your turn.

Here's Wendy's cat asleep in the sunny window, beside a plant. Dora asks: the plant makes its food from the light, so does the cat too?

No, the cat does not. The Sun warms it, but the cat has no leaves and makes no sugar, so it eats.

Now let's look at a cow, which cannot make its own food, so it eats grass all day long.

And now let's look at a hawk. It cannot make its own food, so it eats mice.

And here is a lizard on a warm rock. The Sun warms it, but it makes no food, so it eats insects.

The grass beside the rock makes its own food in its leaves. The lizard cannot.

So, here's what we've seen. An animal cannot make its own food. So an animal must eat plants or other animals.

Okay, now your turn.

Here's Dora at lunch with a glass of milk. Sally says the energy in that milk came from the Sun. Dora laughs: milk is not sunshine! Is Sally right?

Yes, she is. Let's trace the energy back. The Sun's light carries energy to grass, and the grass makes its food.

A rabbit eats the grass, so the energy passes to the rabbit. So the energy in the rabbit's food came from the Sun.

Now let's trace the milk: a cow eats grass, the cow makes milk, and Dora drinks it. So the energy in the milk came from the Sun too.

So, trace the energy back one eater at a time. Every eater got its energy from its food, and every plant got its energy from the Sun's light. So the energy in any food came from the Sun in the end.

Okay, now your turn.

Here's everything we found out about how plants make their own food.

First, a plant makes its own food in its leaves. The leaf uses water from the soil, carbon dioxide from the air, and the energy the Sun's light carries, to make sugar. The sugar is the plant's food.

Next, an animal cannot make its own food. So an animal must eat plants or other animals.

And last, trace the energy back one eater at a time. Every eater got its energy from its food, and every plant got its energy from the Sun's light. So the energy in any food came from the Sun in the end.

Okay, now your turn.

Here's Miss Whitaker's class on a nature walk at the edge of a field in Texas. A rabbit nibbles the grass, a hawk sits on a fence post, and mushrooms grow on a fallen log.

All of them are alive and need food. But the grass eats nothing, the hawk eats meat, and the mushrooms feed on a dead log.

So how does each one get its food? And how does the whole field fit together?

To find out, we will look at how each one gets its food, what happens to dead leaves, and how to read a drawing of what eats what.

Okay, so are you ready to find out who eats what in the field?

Here's Miss Whitaker's class at the edge of a field in Texas. A rabbit nibbles the grass. Seth asks: what does the grass eat?

The rabbit can't make its own food, so it eats the grass. Does the rabbit make its own food? No.

But the grass eats nothing. Its leaves make its food, using sunlight. Does the grass make its own food? Yes.

And now here's the oak tree. Its leaves make its food, using sunlight. Yes.

And here are the pond algae, tiny green things floating on the pond. They make their own food, using sunlight. Yes.

But now look at a green caterpillar on a green leaf. It's green, but it eats the leaf. No.

So, here's what we've seen. A producer is a living thing that makes its own food, using sunlight. Grass, trees and pond algae are producers.

Okay, now your turn.

Here's Miss Whitaker's class at the field. A fox runs past with a mouse, and Sloane says: the rabbit eats grass, but the fox eats a mouse. Do they get their food the same way?

The rabbit can't make its own food, so it eats the grass. Does the rabbit eat other living things? Yes.

And now here's the fox. It can't make its own food either, so it eats the mouse. Yes.

And now a grasshopper chews a blade of grass. It eats another living thing. Yes.

But now look at the grass. It takes in water from the soil, but it eats nothing: it makes its own food. No.

So, here's what we've seen. A consumer is a living thing that gets its energy by eating other living things. A rabbit eating grass and a fox eating the rabbit are both consumers.

Okay, now your turn.

Here's Troy at a fallen log with mushrooms on it. The wood under them is crumbly. He asks: is a mushroom a producer?

A mushroom is not a plant. With no leaves and no green parts, it makes no food. It feeds on the dead log, breaking the wood into bits. Does it feed on dead things? Yes.

And now gray fuzz covers a fallen apple: that fuzz is mold. It feeds on the dead apple, breaking it into bits. Yes.

And tiny living things too small to see feed on dead leaves in the soil. Yes.

But look at the moss on the log. It makes its own food, using sunlight. The log is only where it stands. No.

So, here's what we've seen. A decomposer is a living thing that feeds on dead things, breaking them into tiny bits. Mushrooms and mold are decomposers.

Okay, now your turn.

Here's Troy in October, raking leaves into a tall pile by the back fence.

And here's the same corner in April. The pile is low and crumbly, and the grass around it is thick and green. Troy asks: where did the leaves go?

All winter, decomposers in the pile fed on the dead leaves. Mold and tiny living things too small to see broke them into bits. Without them, the leaves would pile up deeper every year.

The tiny bits went into the soil. These bits are called nutrients. The grass's roots took them in and used them to grow.

The bits are not the grass's food. The grass still makes its own food in its leaves, using sunlight.

So, decomposers break dead things into tiny bits that go into the soil. Plants take those bits in through their roots and use them to grow.

Okay, now your turn.

Here's Miss Whitaker's class, back from the field, with a table of what they saw. Sloane asks: the hawk eats snakes, and the snake eats mice. Do they go in the same group?

Ask how it gets its food. How a living thing gets its food is called its role. The grass makes its own food, using sunlight: a producer.

The rabbit eats grass, so it is a consumer. The snake eats mice, so it is a consumer.

And the hawk eats mice and snakes, so the hawk is a consumer too.

The mushroom feeds on the dead log, so it is a decomposer.

So, to sort a living thing, ask how it gets its food. It makes its own food, using sunlight: a producer. It eats other living things: a consumer. It feeds on dead things, breaking them into bits: a decomposer.

Okay, now your turn.

Here's Seth's food chain poster: grass, a rabbit, a fox. Sloane says the hawk eats rabbits too, and the fox eats mice. Where do they go?

The arrow points from the food to the one that eats it. Let's draw the rabbit once, with an arrow to the fox and one to the hawk. The two chains join.

Here are all the field's chains joined into one drawing. Many food chains joined together make a food web.

What does the hawk eat? Follow the arrows that point into the hawk: from the mouse, the rabbit and the snake.

What eats the grass? Follow the arrows that start at the grass: to the grasshopper, the mouse and the rabbit.

So, to find what a living thing eats, follow the arrows that point into it. To find what eats it, follow the arrows that start at it.

Okay, now your turn.

Here's everything we found out about producers, consumers and decomposers.

First, a producer is a living thing that makes its own food, using sunlight.

Next, a consumer is a living thing that gets its energy by eating other living things.

Then, a decomposer is a living thing that feeds on dead things, breaking them into tiny bits.

And decomposers break dead things into tiny bits that go into the soil. Plants take those bits in through their roots and use them to grow.

To sort a living thing, ask how it gets its food.

And last, a food web is many food chains joined together. To find what a living thing eats, follow the arrows that point into it. To find what eats it, follow the arrows that start at it.

Okay, now your turn.

Here's Sylvia with her grandmother, looking at an old photo of Grandma at nine years old. Grandma had the same dark hair and the same wide smile that Sylvia has now.

But Grandma could knit a whole scarf at nine, and Sylvia cannot knit a stitch.

So which of these did Sylvia get from her family, and which did Grandma get from how she lived?

To find out, we will look at what a living thing gets from its parents, what it gets from how it lives, and whether an animal is born knowing what it does.

Okay, so are you ready to find out where a living thing's traits come from?

Here's Paula with her dog's four new puppies, and every puppy has floppy ears, like its mother. Paula asks why all four puppies have floppy ears.

Something a living thing has or can do, like floppy ears, is called a trait.

The puppies were born with floppy ears, and their mother and father have floppy ears too. So the floppy ears came from the parents.

Now consider Tina with her mother and father: all three have brown eyes. Tina was born with brown eyes, so they came from her parents.

And now consider a sunflower. Its seeds grew into young sunflowers with yellow petals, like the parent, so the yellow petals came from the parent plant.

So, here's what we've seen.

Some traits come from the parents. The living thing has them from the start, and its parents have them too.

Okay, now your turn.

Here's Tina with a small scar on her knee from a bike fall. Nobody else in her family has one, so where did it come from?

The scar was not there from the start. Tina fell, the cut healed, and the scar stayed, so it came from something in her life.

Now consider Paula riding her bike. She was not born riding; she practiced for weeks, so riding came from how she lived.

And now Paula's dog runs with her every morning, and its legs grew strong. So the strong legs came from how it lived.

But Tina's brown eyes were there from the start, like her parents', so those came from her parents.

So, here's what we've seen.

Some traits come from how a living thing lived. It did not have them from the start; something that happened during its life made them.

Okay, now your turn.

Here's Miss Yamamoto with two boxes on the board. One asks: was it there from the start, from the parents? The other asks: did it come from how it lived?

The dog was born with floppy ears, like its parents, so they go in the parents' box.

Paula taught the dog to fetch, so fetching goes in the life box.

The brown coat goes in the parents' box, the strong legs in the life box.

Here's a tricky one. Paula and her dad both ride bikes. But she was not born riding; she learned it, so riding goes in the life box.

The strong legs stay with this dog: its puppies were born without them.

So, a trait a living thing had from the start, from its parents, is called an inherited trait. A trait that came from how it lived is called an acquired trait.

Okay, now your turn.

Here's Sylvia with her tall mother and father. Miss Yamamoto says the food Sylvia ate played a part too, so did her height come from her parents, or from her food?

Inherited traits come from the parents, and acquired traits come from how the living thing lived. But some traits need a third box, because both played a part.

Sylvia's brown eyes go in the parents' box: she was born with them. Her reading goes in the life box: she learned it at school.

Her height came from both: tall parents, and good food while she grew.

A big dog's size came from both too: big parents, and plenty of food as a puppy.

Here's the pattern.

Some traits come from both the parents and how the living thing lived. Its size comes from its parents and from the food it got while it grew.

Okay, now your turn.

Here's Tina in her shed with Paula's dog. A spider spins a perfect web the first time, with nobody to show it. Tina asks how it knows.

Something an animal does, like spinning a web, is a behavior. The spider was born knowing it.

Now Paula says sit, and her dog sits. Paula taught it with treats, so the dog learned it.

A robin chick opens its beak wide the first time a parent lands, so it was born knowing that.

Born knowing a behavior is the same idea as an inherited trait. Picking one up during life is the same idea as an acquired trait.

Sitting on command stays with this dog: its puppies are not born knowing it.

So, a behavior an animal is born knowing is called an instinct. A behavior an animal picks up during its life is called a learned behavior.

Okay, now your turn.

Here's everything we found out about traits from parents, and traits from life.

First, some traits come from the parents. The living thing has them from the start, and its parents have them too.

Next, some traits come from how a living thing lived. It did not have them from the start; something that happened during its life made them.

Then the names. A trait a living thing had from the start, from its parents, is called an inherited trait. A trait that came from how it lived is called an acquired trait. An acquired trait stays with the one that got it.

And some traits come from both the parents and how the living thing lived. Its size comes from its parents and from the food it got while it grew.

Last, a behavior an animal is born knowing is called an instinct. A behavior an animal picks up during its life is called a learned behavior.

Okay, now your turn.

Here's Zoey's backyard in early summer. A pumpkin vine is covered in yellow flowers, and in the hedge a robin sits on three blue eggs.

By fall, pumpkins full of seeds hang where some flowers were, and three grown robins fly from the hedge.

A plant's life and an animal's life both go round in a cycle. But how does a flower turn into a pumpkin full of seeds?

To find out, we will look at how a flower makes its seeds, how seeds travel and start to grow, and why some young animals look nothing like their parents.

Okay, so are you ready to find out how plants and animals go round their life cycles?

Here's Miss Zimmerman's class in the school garden. Tamara watches a bee crawl out of an apple flower dusted with yellow. What is the yellow dust?

Here's the flower cut open. The yellow dust on the little stalks is called pollen, and the taller stalk in the middle has a sticky top.

For the flower to make seeds, pollen has to reach the sticky top of another flower, but pollen can't move by itself.

The bee goes in for the sweet juice. Pollen sticks to its fuzzy body, and some rubs off onto the next flower's sticky top.

Now consider corn. Its flowers have no bright petals, so bees don't visit, and the wind blows its pollen to the next corn plant.

So, pollination is pollen moving from one flower to another, carried by an insect or by the wind.

Okay, now your turn.

Here's Theodore at his uncle's apple orchard in spring. A truck brings rows of beehives. Why bring bees to an orchard?

Here is pollination: the bees carry pollen from flower to flower, and it lands on each flower's sticky top.

A tiny part of the pollen travels down and joins with a tiny part deep inside, in the green cup. That joining is called fertilization.

After fertilization, that tiny part grows into a seed. The petals fall, and the green cup swells into an apple with the seeds inside.

But imagine a flower that no bee visits. No pollen lands, so no seed forms, and no apple grows there.

So, once pollen reaches a flower, that flower can make seeds. The pollen joining with the flower's inside part is called fertilization. A flower that no pollen reaches makes no seeds.

Okay, now your turn.

Here's Tamara in the park. She blows on a dandelion clock, and the fluffy seeds float away. Why does a dandelion send its seeds away?

Imagine every seed dropped right under the parent plant. Dozens of tiny plants would come up in one crowded, shaded patch, and most would die.

But a seed that is carried away lands in its own spot, with space and light of its own.

The wind carries a dandelion seed on its tuft of hairs. Water carries a coconut to a new shore.

A burr hooks onto a dog's fur and rides away. And a bird eats a berry, and the seeds come out in its droppings far away.

So, seeds are carried away from the parent plant by the wind, by water or by animals, so each new plant gets space and light of its own.

Okay, now your turn.

Here's Zoey with three cups of bean seeds on paper towels: cup A damp in the warm dark cupboard, cup B damp in the fridge, cup C dry on the sunny shelf.

Theodore says cup C will grow first, because it has the light. But a week later, only cup A's seeds have split their coats and grown a root.

Cup B had water but was cold, and cup C was warm and in the light but dry. Neither grew.

So a seed needs water and warmth to start, and not light or soil, because the tiny plant inside uses the food packed beside it.

A seed starting to grow is called germination. First the root comes out, then the shoot comes up, then the first leaves open.

So, a seed germinates once it has water and warmth. It does not need light to start.

Okay, now your turn.

Here's the class's butterfly cage, full of caterpillars, and Theodore's jar with a tiny grasshopper. Why does the caterpillar look nothing like a butterfly, when the baby grasshopper does?

A butterfly's life cycle runs egg, caterpillar, chrysalis, butterfly. The young looks nothing like the grown-up, and its body changes completely: a complete change.

A grasshopper's life cycle runs egg, young grasshopper, grown grasshopper. The young looks like a small grown-up: gradual growth.

Now consider a frog and a dog. The tadpole is the young frog, and it looks nothing like one: a complete change. A puppy looks like a small dog: gradual growth.

So, if the young looks nothing like the grown-up, and its body changes completely, the life cycle is a complete change. If the young looks like a small grown-up, and just grows bigger, the life cycle is gradual growth.

Okay, now your turn.

Here's everything we found out about life cycles of plants and animals.

First, pollination is pollen moving from one flower to another, carried by an insect or by the wind.

Next, once pollen reaches a flower, that flower can make seeds.

The pollen joining with the flower's inside part is called fertilization. A flower that no pollen reaches makes no seeds.

Then, seeds are carried away from the parent plant by the wind, by water or by animals, so each new plant gets space and light of its own.

Next, a seed starting to grow is called germination. A seed germinates once it has water and warmth, and it does not need light to start.

And last, an animal's life cycle comes in two kinds. If the young looks nothing like the grown-up, and its body changes completely, the life cycle is a complete change.

If the young looks like a small grown-up, and just grows bigger, the life cycle is gradual growth.

Okay, now your turn.

Here's Travis, in Florida for winter break, on a video call with Kayla, in Minnesota for hers.

It is January. Out of Kayla's window, snow covers the ground and the maple is bare. Out of Travis's window, the oak is green.

Travis asks: why does the same January look so different?

At home on Travis's shelf sits a sea shell in a rock, from the time his dry town was under the sea.

To find out, we will look at winter, and spring, in different places, what a fossil tells about long ago, and what happens to a kind of living thing when its place changes.

Okay, so are you ready to find out what happens when a place changes?