Grade 3 Science — every video script

Here is an explorer, deep in the jungle.

She is hunting for buried treasure.

Her map says: the treasure is near the big rock.

She finds the big rock. But which side? How far?

She digs on the left. Nothing. She digs on the right. Nothing.

"Near the big rock" was not enough. What words were missing?

Now let's leave the jungle. Here is a race track.

A race car goes around the track, again and again.

Where will the car be in ten seconds? Can you say, before it gets there?

That is what this topic is about: where things are, how they move, and where they will be next.

Okay, so are you ready to dive in?

Mia has hidden a ball somewhere in this room.

She tells Sam, "The ball is over there."

Sam looks all around. He can't find it.

Now Mia says, "The ball is under the teacher's desk."

Sam walks straight to it.

That worked, because everyone in the room can see the desk.

An object everyone can see, that you use to say where something is, is called a reference point.

Where the ball is, compared to the desk, is called its position: under the desk.

And now, a hat. The hat is on the desk.

The desk is the reference point. The hat's position is on the desk.

And now, a box. The box is behind the door.

The door is the reference point. The box's position is behind the door.

So here is the rule. To say where something is, name a reference point, then say where your object is compared to it.

Suppose Sam says, "The ball is two steps away."

Two steps away from what?

From Sam? From the door? From the window?

Sam has not said.

Nobody can find the ball. This description has no reference point.

Now Sam says, "The ball is two steps away from the door."

The door is the reference point. Now everyone knows where to look.

And now, "The hat is on the desk." The desk is the reference point.

And now, "The box is behind the door." The door is the reference point.

But now, "The box is over there." Over there is not an object anyone can see. No reference point.

So here is the rule. To check a description, ask: away from what?

If there is no answer, the description has no reference point.

Suppose a toy car sits somewhere near the classroom door.

"Near the door" is not enough. There is a lot of floor near the door.

You need to say how far from the door, and which way.

First, name the reference point. The door.

Next, say how far. Count the steps from the door to the toy car.

One step. Two steps.

Then say which way. The toy car is to the left of the door.

Put it together. The toy car is two steps to the left of the door.

How far is called the distance.

Which way is called the direction.

And now, the same toy car in a new place. The toy car is four steps to the right of the window.

The window is the reference point. Four steps is the distance. To the right is the direction.

Now the description means only one spot.

And now, a checkers board. The red piece is two squares to the right of the black piece.

So here is the rule. Say the reference point, then the distance, then the direction.

Here is a toy car by the wall. Watch carefully.

Look away. Look back. The car is still by the wall.

Its position is the same.

The car did not move.

But now, look away. Look back. The car is nearer the door.

Its position changed.

The car moved, even though nobody saw it roll.

And now, a snail on the sidewalk. Look away. Look back.

The snail has crept forward a little.

Its position changed. The snail moved, even though it moved slowly.

And now, a cat asleep on a mat. Look away. Look back.

The cat lies on the chair.

Its position changed. The cat moved.

But now, the cat again, asleep on the chair. Look away. Look back.

The cat still lies on the chair.

Its position is the same. The cat did not move.

And now, a red piece on a checkers board. Look away. Look back.

It sits on a new square. Its position changed. It moved.

So here is the rule. If its position changed, it moved.

If its position stayed the same, it did not move.

Suppose a toy car rolls from a starting line and stops.

Two friends argue.

One friend says, "It rolled a long way!" The other friend says, "No, only a short way!"

The only way to know is to measure the distance with a ruler.

First, mark where the front of the toy car started. That is the start mark.

Next, mark the front of the toy car again, where it stopped. That is the stop mark.

Now lay the ruler along the floor, from the start mark to the stop mark.

The zero on the ruler sits at the start mark.

Read the number at the stop mark. Forty.

The toy car rolled forty centimeters.

And now, the same toy car rolls again, and stops sooner.

Zero sits at the start mark. Read the stop mark.

Thirty centimeters.

So here is the rule. Put the ruler's zero on the start mark, where the front of the toy car was before it moved, then read the ruler at the stop mark.

The number at the stop mark is how far it moved.

Here is a shelf, with a ruler taped along its edge.

In the morning, a seashell sits at the twelve centimeter mark.

At bedtime, the same shell sits at the twenty-eight centimeter mark.

It moved. But how far?

The stop mark reads twenty-eight centimeters. But the shell did not start at zero, so twenty-eight centimeters is not how far it moved.

When the zero is not at the start, read both marks.

Read the start mark. Twelve centimeters.

Read the stop mark. Twenty-eight centimeters.

Then find the difference. From twelve centimeters up to twenty-eight centimeters is sixteen centimeters.

The shell moved sixteen centimeters.

And now, let's look at a toy duck on the kitchen table.

The duck slides along the table, from the twenty mark to the forty-five mark.

From twenty centimeters up to forty-five centimeters is twenty-five centimeters. The duck moved twenty-five centimeters.

So here is the rule. When the zero is not at the start, read the start mark and the stop mark, then find the difference.

That difference is how far it moved.

Okay, now your turn.

Here is a ball on the floor. Watch as it rolls to a friend.

The dotted line shows where the ball went. That line is called the ball's path.

This path does not bend. This path is straight.

And now, the child throws the same ball to the friend.

This path bends. This path is curved.

And now, a toy train going around its track.

This path bends all the way around and comes back to where it began. This path is curved.

And now, a sled sliding down a snowy hill.

This path does not bend. This path is straight.

So here is the rule. The line a moving object travels along is its path.

A path that does not bend is straight. A path that bends is curved.

Okay, now your turn.

The ball and the toy car. Here is everything we found out.

To say where something is, name a reference point. The ball is under the desk.

A reference point is an object that helps you say where something is.

Where something is, compared to a reference point, is its position.

A description with no reference point does not tell you where to look. "The ball is over there" tells you nothing.

To give a position exactly, say the reference point, the distance and the direction. Two steps to the left of the door.

If its position changed, it moved. If its position stayed the same, it did not move.

Even a slow snail moves. Its position changes a little at a time.

To measure how far it moved, put the ruler's zero at the start mark and read the stop mark. Forty centimeters.

The line a moving object travels along is its path. A path is straight or curved.

That is the whole topic: where things are, whether they moved, and how far they moved.

It's Sports Day.

Maya wins the first race of the morning.

Leo wins the last race of the afternoon.

Both ran the same race track, but never side by side.

Their friends argue: who's faster?

Can you tell, when they never raced each other?

Now let's look up.

A plane crosses high overhead. It looks slow, slower than a bird flying past.

But in one minute, that plane goes farther than you could walk in two hours.

Is the plane slow, or does it only look slow?

This topic is about fast and slow: how to tell which is faster, and how things speed up or slow down.

Okay, so are you ready to find out who's fastest?

Here is a marble on the kitchen floor.

Someone taps it, and it rolls.

Let's take a photo every second.

Click. In the first photo, the marble is by the fridge.

Click. Now it's by the table leg.

Click. Now it's by the door.

In every photo, the marble is somewhere new.

Between the photos it was rolling too, so every moment its position was changing.

And now, the marble stops by the door.

Click. Click. Two photos, the same place.

Its position is not changing, so it is not moving.

And now, a bus drives past the school. Click, click, click.

Somewhere new in every photo.

And now, the minute hand of the classroom clock, a minute apart.

The hand is somewhere new. Slow, but moving.

So here is the rule. A moving object is always changing its position. Each moment, it is somewhere new.

Okay, now your turn.

Here is a ball on the gym floor.

You push it, and it rolls toward the wall.

It hits the wall, and now it rolls away, another way.

The ball changed direction.

The corner in its path is where the direction changed.

And now, the same ball with no wall in the way.

Its path is straight. It did not change direction.

And now, a car turning left at a corner.

Its path has a corner. The car changed direction.

And now, a dog runs to the tree, turns around, and runs back.

There and back: the dog changed direction.

But now, the same dog runs to the tree and stops.

Stopping is not turning, so the dog did not change direction.

So here is the rule. A straight path means the direction did not change. A corner or a bend shows where it changed.

Okay, now your turn.

Here are two wind-up toys on a start line.

Go! Both set off together.

Ten seconds. Stop!

Let's lay a meter stick along the floor.

The frog went 80 centimeters. The duck went 30.

The same ten seconds, and the frog went farther, so it is faster.

And now, two snails for one minute: 12 centimeters and 4.

The same time, and the big snail went farther, so it is faster.

And now, Priya and Zara, walking for 20 seconds: 30 meters and 24.

The same time, and Priya went farther, so Priya is faster.

But now, the frog moves for 10 seconds and the duck for 20.

The times are different, so this does not tell you.

So here is the rule. Faster means farther in the same time. Give two objects the same time. The one that goes farther is faster.

Okay, now your turn.

It's Sports Day. Here are Ana and Ben.

Each runs from the fence to the tree: 20 meters for both.

A friend times them.

Ana runs. Six seconds.

Ben runs. Nine seconds.

Ben took longer. Is Ben faster?

No. Ana took less time over the same distance, so Ana is faster.

A longer time means slower, not faster.

And now, two toy boats cross the same pool: 8 seconds and 5.

Less time, so the white boat is faster.

And now, two snails along the same wall: 40 seconds and 25.

Less time, so the small snail is faster.

But now, Ana runs 20 meters and Ben runs 40.

Different distances, so their times do not tell you.

So here is the rule. Faster also means less time over the same distance. Give two objects the same distance. The one that takes less time is faster.

Okay, now your turn.

Here are two runners, Jo and Max.

Let's drop a mark at each tick.

One second: Jo goes 2 meters, Max goes 7.

Two seconds: another 2, another 7.

In each second, Jo goes 2 meters. In each second, Max goes 7 meters.

How far something goes in each second is called its speed.

Max goes farther in each second, so Max has the greater speed.

And now, a horse and a cheetah: about 15 meters in each second, and about 30.

The cheetah has the greater speed.

And now, a normal car and a race car: about 25 meters in each second, and about 75.

The race car has the greater speed.

But now, "the car went 100 meters" is a distance, not a speed.

So here is the rule. How far something goes in each second is its speed. Faster means a greater speed.

Okay, now your turn.

Here are a snail, a walker and a cyclist on the same straight path.

Each one moves for one minute.

The snail goes 1 meter. The walker goes 80. The cyclist goes 300.

For a slow mover like the snail, we count a whole minute instead of a second. The rule is the same: the same time for everyone.

Let's line them up from fastest to slowest.

Who went farthest? The cyclist, 300 meters. So the cyclist is the fastest.

Who went the shortest distance? The snail, 1 meter. So the snail is the slowest.

The walker sits in between.

So, give everyone the same time. Whoever went farthest is the fastest. Whoever went the shortest distance is the slowest.

Okay, now your turn.

A car waits at a red light.

The light turns green. The car moves off. A mark drops at each tick.

In the first second, it goes 1 meter.

In the next second, it goes 2 meters.

In the third second, it goes 3 meters.

Each second, it goes farther than the second before.

Going farther in each second than the second before is called speeding up.

But now, the same car on the same road goes 5 meters, 5 meters, 5 meters.

It goes the same distance each second. It is not speeding up.

And now, a snail goes 1 centimeter, 2 centimeters, 3 centimeters. Slow things speed up too.

But now, a fast train goes 30 meters, 30 meters, 30 meters, and is not speeding up.

So, here's what we've seen. Going farther in each second than the second before is called speeding up.

Okay, now your turn.

A child pushes a toy car along the floor. A mark drops at each tick.

In the first second, the toy car goes 3 meters.

In the next second, it goes 2 meters.

In the third second, it goes 1 meter.

Each second, it goes less far than the second before.

Going less far in each second than the second before is called slowing down.

But now, a car on a road goes 5 meters, 5 meters, 5 meters.

It goes the same distance each second. It is not slowing down.

And now, a bus about to stop goes 10 meters, 6 meters, 2 meters. The bus is slowing down.

But now, a slow snail goes 1 centimeter, 1 centimeter, 1 centimeter. It is not slowing down.

So, here's what we've seen. Going less far in each second than the second before is called slowing down.

Okay, now your turn.

Here is a toy train on a flat, straight track.

Let's drop a mark at each tick.

One second: 2 meters.

Two seconds: 2 meters.

Three seconds: 2 meters again.

Each second, the same distance as the second before.

Its speed is not changing. Going the same distance in every second is called keeping the same speed.

But now, the same train down a slope: 2 meters, 3, 4. Farther each second, so not the same speed.

And now, a race car: 60 meters, 60, 60. A fast mover keeping the same speed.

And now, a snail: 1 centimeter, 1, 1. A slow mover keeping the same speed.

But now, the same snail stops: 1, 1, then nothing. Not the same speed.

So here is the rule. Going the same distance in every second is called keeping the same speed. Fast or slow, either can.

Okay, now your turn.

Back to Sports Day. Here is everything we found out.

A moving object is always changing its position. Each moment, a runner is somewhere new.

A corner or a bend in the path shows where the direction changed. A straight path means it did not.

Faster means farther in the same time. Give two things the same time and see which goes farther.

Faster also means less time over the same distance. Maya and Leo both ran 50 meters.

Maya took 10 seconds. Leo took 12 seconds. Less time over the same distance, so Maya is faster, even though they never raced side by side.

How far something goes in each second is its speed.

The plane goes about 250 meters in each second. The bird goes about 10.

The plane has the far greater speed. It only looks slow.

To put things in order from fastest to slowest, give them the same time. Whoever went farthest is the fastest, and whoever went the shortest distance is the slowest.

Going farther in each second than the second before is speeding up. Leo rides home on his bike: 2 meters, then 3, then 4.

Going less far in each second than the second before is slowing down.

Going the same distance in every second is keeping the same speed. Fast or slow, either can.

That is the whole topic: faster means farther in the same time, and also less time over the same distance. You know what speed means, and how a speed can change.

Here's a playground. A boy lets go of his ball, and it falls.

Everything you let go of falls.

But have you ever wondered why things fall down, and not up?

Imagine a world where things fell up. The boy lets go, and his ball floats up into the sky.

That drawing is wrong. On Earth, things fall down. Every time.

Beside him, a girl hangs upside down from the bar. Her hair hangs toward the ground.

Something pulls her hair down. Which parts of her does it pull on?

To find out, we will look at why things fall, and which parts of you get pulled.

Okay, so are you ready to find out why things fall down?

Here is an apple, held out in a hand.

The hand opens, and the apple falls to the floor.

No hand pushed it. No string pulled it.

Nothing touched it on the way down. So what made it fall?

Earth pulled the apple down, without touching it.

We call this pull Earth's pull.

This pull happens because of something called gravity. You'll find out more later.

And now, a ball. You let go, and it falls to the floor.

Earth pulled it down.

And now, a child jumps up and comes back down.

And now, you throw a ball up. It comes back down.

Earth was pulling it down the whole time, even on its way up.

So here is the rule. Earth is always pulling on every object.

So every object you let go of falls to the ground.

Okay, now your turn.

Here is a book resting on a table. It isn't moving.

Is Earth pulling on the book right now?

Yes. Earth is pulling the book down.

The table is in the way, so the book stays where it is.

And now, a ball you've thrown up. It's still going up.

Earth is pulling on the ball, even now.

That's why it comes back down.

And now, a car moving along the road.

Earth is pulling on the car, the whole time.

And now, a leaf falling from a tree.

Earth is pulling on the leaf.

Still, moving up, moving along, moving down: Earth is pulling on every one.

So here is the rule. Earth is always pulling on every object, moving or still.

Okay, now your turn.

Earth pulls every object down, all the time.

Earth's pull has a name. Earth's pull is called gravity.

Gravity pulls the apple down.

Gravity pulls the book down onto the table, even while the book sits still.

And here's a ball you've thrown up, still going up. Gravity pulls it down, even now.

Earth's pull and gravity are two names for the same pull. From now on, we use both.

So, Earth's pull is called gravity. Gravity is pulling on every object, all the time.

Okay, now your turn.

Here's a ball you've just thrown straight up.

Earth is pulling on it. But which way?

Straight down, toward the ground.

And now, a rocket flying through the sky. Which way does Earth pull it?

Straight down, toward the ground.

And now, a car moving along the road. Which way does Earth pull it?

Straight down, toward the ground.

And now, a lamp hanging from the ceiling. Which way does Earth pull it?

Straight down, toward the ground. The cord holds it up.

So here is the rule. Earth's pull always points straight down, toward the ground.

Okay, now your turn.

Imagine you're standing on the floor.

Earth pulls you down, so your feet press the floor.

But your nose and hair don't press on anything.

So which parts of you does Earth pull on?

Hold your arm straight out. Now let it go floppy.

Your arm drops to your side, and nothing touched it.

Earth pulled your arm down. That's Earth's pull.

And now, a girl on a bar in the playground.

She swings up and hangs upside down.

Her hair hangs down toward the ground. Earth pulls her hair down.

Her face goes red: Earth pulls the blood in her down too.

Earth pulls on her hands too.

And now, one hair comes loose and drifts down.

Earth pulls even one hair.

So here is the rule. Earth pulls on every part of you. It pulls your nose and your hair, not only your feet.

Okay, now your turn.

Here is a ball on the floor.

You pick it up.

But Earth still pulls it down. How did it go up?

Your hand pulls it up. Earth pulls it down.

Your pull is strong enough to beat Earth's pull. Up it goes.

Now you let go. The ball falls.

And now, a plane takes off. Its wings push it up, and that push is strong enough.

And now, a bungee jumper falls from a bridge. The cord pulls her up.

Her fall slows down. So the cord's pull is strong enough to beat Earth's pull.

But now, a boy pulls on a big rock, and it stays. His pull is not strong enough.

Here's the rule. A push or a pull that is strong enough beats Earth's pull.

When the push or pull stops, only Earth's pull is left, and the object falls.

Okay, now your turn.

The apple, the book on the table, the girl on the bar, and the ball in your hand. Here is everything we found out.

You open your hand, and the apple falls. Nothing touched it.

Earth pulls every object down, without touching it. We call this pull Earth's pull.

Now the book on the table. It sits still, but Earth is pulling on it.

Earth is always pulling on every object, moving or still.

And which way? Earth's pull always points straight down, toward the ground.

Now the girl on the bar. She hangs upside down, and her hair hangs toward the ground.

Earth pulls on every part of you, not only the part touching the ground.

Now the ball in your hand. Your hand pulls it up, and Earth pulls it down.

A push or a pull that is strong enough beats Earth's pull, so the ball goes up.

When the push or pull stops, only Earth's pull is left, and the object falls.

The crane's pull and the rocket's push were strong enough. The boy's pull on the rock was not.

The bungee cord's pull was strong enough too. It slowed the jumper's fall.

And Earth's pull has a name. Earth's pull is called gravity.

Gravity pulls everything straight down, all the time.

That is the whole topic: why everything falls down, which way Earth pulls, and how anything ever gets back up.

Here's a paperclip on a table.

A magnet comes down toward it, and stops just above.

Nothing touches the paperclip. Watch.

It jumps! Up it goes, and sticks to the magnet.

Nothing touched it. So what pulled it up?

Now let's go to the kitchen. A drawing hangs on the fridge door, held by one small magnet.

Nobody is holding it. Why doesn't it fall?

Now let's look at two toy train cars. One rolls toward the other.

Before they touch, the other car rolls away! What pushed it?

That's this topic: what a magnet pulls, what it pushes, and how a magnet can solve a problem.

Okay, so are you ready to find out what a magnet can do?

Here's a paperclip on a table, and a magnet hanging just above it.

Nothing touches the paperclip. Watch.

It jumps up and sticks to the magnet.

What pulled it up? The magnet did, without touching it.

That's the magnet's pull.

The paperclip is made of steel. Does a magnet pull everything?

Here's a plastic paperclip. The magnet comes close, and it stays.

The magnet does not pull plastic.

And now a steel nail. It jumps up, so the magnet pulls steel.

And now an empty soup can, made of steel. It rolls to the magnet.

But now a soda can, made of aluminum, a different metal. It stays.

So here's the rule. A magnet pulls steel without touching it.

A magnet does not pull plastic, wood, paper or aluminum.

Okay, now your turn.

Here are two magnets on a table. You slide one toward the other.

Before they touch, the other magnet slides to meet it. They snap together.

Your magnet pulled it, without touching. The two magnets pull together.

Now you turn your magnet around and slide it close again.

This time the other magnet slides away, before they touch!

Your magnet pushed it, without touching. The two magnets push apart.

If you turn one magnet around, pull changes to push.

And now a steel nail. The magnet comes close, and the nail slides to it.

You turn the magnet around. The nail still slides to it.

A magnet never pushes steel away. Only another magnet can be pushed away.

So here's the rule. Two magnets can pull together or push apart, without touching.

If you turn one magnet around, pull changes to push.

Okay, now your turn.

Here's a cupboard door that won't stay shut.

How can a magnet solve this problem? Ask two questions.

One: what must it pull? The door is wood, and a magnet does not pull wood.

So we add a steel piece: a small plate. Now there's steel to pull.

Two: where must the magnet go? Right where the plate lands when the door shuts.

The door shuts. The magnet pulls the plate, and the door stays shut.

And now, pins on a carpet. They're steel already.

The magnet goes just above the carpet, and the pins jump up to it.

And now, two train cars. A magnet on each end, and they pull together.

But a plastic button? A magnet does not pull plastic, so it can't help.

So here's the rule. Put the magnet where its pull does the job: near steel, or near another magnet.

Okay, now your turn.

The paperclip, the two magnets, and the cupboard door. Here is everything we found out.

The magnet hung just above the paperclip, and the paperclip jumped up to it.

A magnet pulls steel without touching it.

Paperclips, nails and soup cans are steel, and the magnet pulls them all.

A magnet does not pull plastic, wood, paper or aluminum.

The soda can is metal, but it's aluminum, not steel. It stays where it is.

Now the two magnets on the table. One slides toward the other, and they snap together.

Two magnets can pull together or push apart, without touching.

If you turn one magnet around, pull changes to push.

And the toy train car that rolled away? The magnet on the other car pushed it, without touching.

A magnet never pushes steel away. Only another magnet can be pushed away.

Now the cupboard door. It's wood, so we added a steel plate.

The magnet on the frame pulls the plate, and the door stays shut.

To solve a problem with a magnet, put the magnet where its pull does the job: near steel, or near another magnet.

If there is no steel, add a steel piece.

And the drawing on the fridge? The fridge door is steel.

The magnet pulls the door, and the drawing is held between them.

That's the whole topic: what a magnet pulls, what it pushes, and how you can use it.

Here's an apple tree. An apple comes loose and falls.

Earth pulled it down.

Now here's a magnet, hanging over a paperclip. The paperclip jumps up and sticks to it.

The magnet pulled it.

And here's a girl at a heavy door. She pushes, and the door swings open.

Earth. A magnet. A girl. Three very different things.

Earth pulls without touching. The magnet pulls without touching. The girl pushes with her hands.

So what do these three have in common?

That's this topic: one word for every push and every pull, what it acts on, and which way it goes.

Okay, so are you ready to find out what pushes and pulls have in common?

Here is an apple falling from a tree. Earth pulls it down.

A pull on the apple. That is a force.

And now, a magnet above a paperclip. The paperclip jumps up.

The magnet pulls the paperclip.

A pull on the paperclip. That is a force.

And now, a boy pushes a door.

A push on the door. That is a force.

But now the same boy just looks at the same door.

No push, no pull. That is not a force.

And now, a girl pulls a wagon.

A pull on the wagon. That is a force.

But now a child shouts at a ball. Words are not a push or a pull.

That is not a force.

So here is the rule. Any push or pull on an object is called a force.

Earth's pull, a magnet's pull, and your push are all forces.

Okay, now your turn.

Here is the boy at the door again. He pushes it, and it swings away from him.

Now he pulls it, and it swings toward him.

Both are forces. But they're not the same.

So what's the difference?

The boy pushes the door. The door moves away from him.

That is a push.

And now, the girl pulls the wagon. The wagon moves toward her.

That is a pull.

And now, a child kicks a ball. The ball moves away from her foot.

That is a push.

And now, the magnet pulls the paperclip. The paperclip moves toward the magnet.

That is a pull.

And now, a girl opens a fridge door. The door moves toward her.

That is a pull.

So here is the rule. A push is a force away from the pusher.

A pull is a force toward the puller.

Okay, now your turn.

A girl stands behind a swing. She pushes it, and it goes forward.

Her push is a force. But a force on what?

On the swing? On the girl?

Let's look at some forces.

A boy pushes a door open. The force is the push.

It acts on the door.

A girl pulls a wagon. The force is the pull.

It acts on the wagon.

A bat hits a baseball. The force is the bat's push.

It acts on the ball.

The wind blows a leaf off a branch. The force is the wind's push.

It acts on the leaf.

And now, Earth pulls an apple down. The force is Earth's pull.

It acts on the apple.

So here is the rule. Every force acts on one object.

You should always be able to name that object.

The girl's push acts on the swing.

Okay, now your turn.

Imagine you pull a drawer open. It comes toward you.

Now you push it shut. It goes away from you.

So which way does each force act?

Let's start with Earth. Earth pulls a dropped apple straight down.

The force has a direction. The direction is down.

A child pushes a door open, away from her. The direction of the force is away from her.

The wind blows a kite to the right. The direction of the force is to the right.

A magnet pulls a paperclip toward itself. The direction of the force is toward the magnet.

But now, a light bulb shines in every direction at once.

Light is not a push or a pull. Light is not a force.

Here is the rule. Every force has a direction, the way it pushes or pulls.

One force acts in one direction at one time.

Okay, now your turn.

The apple, the paperclip, and the door. Here is everything we found out.

Earth pulls the apple. The magnet pulls the paperclip. The boy pushes the door.

Any push or pull on an object is called a force.

Earth's pull, a magnet's pull, and your push are all forces.

Looking at a door is not a force. Shouting at a ball is not a force.

Now, push or pull? The boy pushes the door, and it moves away from him.

A push is a force away from the pusher.

The girl pulls the wagon, and it moves toward her.

A pull is a force toward the puller.

Now, what does a force act on? The bat hits the ball. The bat's push acts on the ball.

Every force acts on one object. You should always be able to name it.

And in which direction does a force act? Earth pulls the apple down. The wind blows the kite to the right.

Every force has a direction, the way it pushes or pulls.

One force acts in one direction at one time.

So Earth pulls, the magnet pulls, and the girl pushes. Each one is a force.

Here's a girl at a table. She holds a magnet above a paper clip, and the clip jumps up.

The magnet never touched it.

Now let's go outside. A boy kicks a ball. His foot has to touch the ball to move it.

So some forces have to touch, and some don't. Which ones? And are there any more that don't?

Now let's go back inside. The girl rubs a balloon on her sweater and holds it over her friend's head.

Her friend's hair rises up toward it! Nothing touched her hair. What's pulling it?

That's this topic: forces that touch, and forces that don't.

Okay, so are you ready to find out which forces don't need to touch?

Here's a ball on the floor. A hand pushes it.

The hand touches the ball. The hand's push is a force that touches.

Now the hand picks the ball up and lets go. Earth pulls it down.

Earth doesn't touch the ball. Earth's pull is a force that doesn't touch.

And now, a paper clip. A magnet hangs just above it.

The clip jumps up. The magnet pulls it, without touching it.

The magnet's pull is a force that doesn't touch.

Now the magnet moves away. The clip falls.

Earth pulls it down, without touching it.

Earth's pull is a force that doesn't touch.

But now, a finger pushes the clip. The finger touches the clip.

The finger's push is a force that touches.

Here's the rule. Most pushes and pulls touch.

But some forces act without touching: Earth's pull, and a magnet's pull.

Okay, now your turn.

Here's a girl. She holds a balloon just above her head.

Her hair stays flat. The balloon isn't pulling on it.

Now she rubs the balloon hard on her sweater.

Then she holds it just above her head again.

Her hair rises up toward the balloon! The balloon doesn't touch her hair.

The rubbed balloon pulls her hair up, without touching it.

And now, tiny bits of paper. The rubbed balloon hangs above them.

The bits jump up toward the balloon. The rubbed balloon pulls them, without touching them.

And now, an empty can on a table. The rubbed balloon comes near.

The can rolls toward the balloon. The rubbed balloon pulls it, without touching it.

Here's the rule. A rubbed balloon pulls light things toward it, without touching them.

It happens because of something called electric charge. You'll learn about that later.

Okay, now your turn.

Here are two forces. A boy kicks a ball, and Earth pulls a diver down.

Which of them touch? Ask one question: does the pusher or puller touch the thing?

The foot kicks the ball. Does the foot touch the ball?

Yes. So the kick is a force that touches.

Earth pulls the diver down. Does Earth touch the diver?

No. So Earth's pull is a force that doesn't touch.

And now, a rubbed balloon pulls a girl's hair up. Does it touch her hair?

No. So the balloon's pull is a force that doesn't touch.

And now, a girl pulls a wagon by its handle. Does her hand touch the handle?

Yes. So her pull is a force that touches.

Here's the rule. Earth's pull, a magnet's pull and a rubbed balloon's pull act without touching.

Most other pushes and pulls touch.

Okay, now your turn.

The hand and the ball, the magnet and the clip, the girl and the balloon. Here is everything we found out.

A hand pushes a ball along the floor. The hand touches the ball.

Most pushes and pulls touch the thing they move. A kick, a pull on a wagon's handle, a push on a door.

Now the hand lets go, and Earth pulls the ball down. Earth doesn't touch the ball.

A magnet pulls a paper clip up, and never touches it.

Some forces act without touching: Earth's pull, a magnet's pull, and a rubbed balloon's pull.

Now the balloon. Before the rub, it pulled nothing. Her hair stayed flat.

After the rub, her hair rose up toward it. The bits of paper jumped up. The can rolled toward it.

A rubbed balloon pulls light things toward it, without touching them.

That happens because of something called electric charge. You'll learn about it later in the course.

So how do you sort a force? To sort a force, ask one question: does the pusher or puller touch the thing?

Yes: a force that touches. No: a force that doesn't touch.

Earth's pull, a magnet's pull and a rubbed balloon's pull act without touching. Most other pushes and pulls touch.

That is the whole topic: forces that touch, and forces that don't.

Here's a ball on the grass. It sits still. Nobody touches it, and it doesn't move.

Now the boy runs up and kicks it. Off it goes!

It rolls straight toward a girl. She stops it with her foot.

Then she taps it to the side, and it rolls off in a new direction.

It took a kick to start the ball moving. But what did it take to stop it? And to turn it?

Did those need a push too?

That's this topic: what a push or a pull can change. Whether a thing moves, its direction, and even its shape.

Okay, so are you ready to find out what a push or a pull can change?

Here's a swing. Nobody touches it, and it hangs still.

Now a girl pushes the seat. The swing starts moving.

Her push started it moving.

And now, a wagon. It sits still on the path.

A boy pulls its handle, and the wagon starts moving. His pull started it moving.

And now, a steel nail on a table. It lies still.

Someone holds a magnet near it. The nail starts sliding toward the magnet.

The magnet's pull started it moving, without touching it.

But now the magnet is gone. Nothing pushes or pulls the nail.

It stays still.

So here's the rule. A push or a pull can start a still thing moving.

With no push or pull, a still thing stays still.

Okay, now your turn.

Suppose a ball rolls across the floor toward a girl.

Her hands push against the ball, against the direction it moves. The ball stops.

Her push stopped it.

But now, the same ball rolls, and nobody touches it. It rolls on past her.

And now, a sled slides along the snow. A boy holds its rope and pulls back, against the direction it moves.

The sled slows down, then stops. His pull stopped it.

And now, a swing swings toward a girl. She holds the seat.

Her hands push against it, and the swing stops.

So here's the rule. A push or a pull against the direction a thing moves slows it down, or stops it.

Stopping needs a force too.

Okay, now your turn.

Imagine a ball rolling straight along the grass.

A boy's foot pushes it from the side, and the ball turns, away from his foot. Now it rolls in a new direction.

His push from the side changed its direction.

But now, the same ball rolls, and nobody touches it. It keeps rolling straight.

And now, a wagon rolls along a path. A girl pulls its handle to the left.

The wagon turns left. Her pull from the side changed its direction.

And now, a toy boat drifts across a pond. The wind pushes it from the side.

The boat turns. The wind's push from the side changed its direction.

So here's the rule. A push or a pull from the side sends a moving thing onto a new path.

It changes direction.

Okay, now your turn.

Look at this ball of clay. A girl squeezes it in her hands.

Now it's flat. Her push changed its shape.

And now, a rubber band. A boy pulls its two ends apart.

It gets longer. His pull changed its shape.

And now, a sponge. A boy presses down on it.

It gets squashed flat. His push changed its shape.

But now, the girl squeezes a wooden block, just as hard. It stays the same shape.

Not everything changes shape. But many things do.

So here's the rule. A push or a pull can change a thing's shape.

Okay, now your turn.

The swing, the caught ball, the pushed ball, and the clay. Here's everything we found out.

A swing hangs still. Nobody touches it. It stays still.

A girl pushes the seat, and the swing starts moving.

A push or a pull can start a still thing moving. With no push or pull, a still thing stays still.

Now a ball rolls toward a girl. Her hands push against it, against the direction it moves. It stops.

A push or a pull against the direction a thing moves slows it down, or stops it. Stopping needs a force too.

Now a ball rolls straight, and a foot pushes it from the side. It turns onto a new path.

A push or a pull from the side sends a moving thing onto a new path. It changes direction.

Now a girl squeezes a ball of clay, and it's flat. A boy pulls a rubber band, and it's longer.

A push or a pull can change a thing's shape.

So, back to the kicked ball. The kick started it. Her foot pushed against it and stopped it. Her tap from the side turned it.

Stopping and turning needed a push too. That's the whole topic: a push or a pull can start a thing, stop it, turn it, or change its shape.

Here's a boy with a soccer ball. He taps it with his foot.

The ball rolls a little way and stops.

Now he kicks the same ball as hard as he can. It flies across the field!

Same ball. Same foot. So what was different?

Now let's look at a drawing of the two kicks.

You can see the boy and the ball, but not the kick. How would you draw it? And how would you show one kick was harder?

That's this topic: how a stronger push makes a bigger change, and how to draw a force as an arrow.

Okay, so are you ready to find out how to draw a push you can't see?

Here's a toy car, sitting still. Now a hand gives it a gentle push.

The car rolls forward, but only a little. A gentle push makes a small change.

And now, the same toy car. This time, the hand gives it a stronger push.

Watch how it rolls farther and faster. That's a bigger change in motion.

And now, the strongest push of all. Look, the car zooms across the floor.

The strongest push makes the biggest change.

The same car, three different pushes.

A gentle push makes a small change, a stronger push makes a bigger change, and the strongest push makes the biggest change.

So here's the rule. Every force has a strength.

The stronger the force, the bigger the change in motion.

Okay, now your turn.

Here's a girl pushing a big box. You can see the box, but not the push.

So how do you draw a push?

We draw a force as an arrow, called a force arrow.

The arrow starts on the box, right in its middle.

It points in the direction the push acts, to the right.

And now, a boy pulls the box with a rope. The arrow starts in the box's middle, pointing left.

Now, Earth's pull on a falling ball. Its arrow starts in the ball's middle, pointing down.

But now, this arrow is drawn wrong. It floats in the air, not on the box, so it doesn't show the push.

This arrow is drawn wrong too: she pushes right, but it points left, the wrong direction.

Here's the rule. Draw the arrow on the object, starting in its middle, pointing in the force's direction.

Okay, now your turn.

Here's a boy pushing a box. First he pushes it gently.

Then he pushes the same box harder. How do you draw the harder push?

For the gentle push, draw a short arrow.

For the harder push, draw a longer arrow.

Both start on the box and point right. Only the length differs.

A longer arrow shows a stronger force.

Line up their left ends. The longer one is the stronger push.

And now, a girl pulls a wagon gently, then harder. The harder pull gets the longer arrow.

Now, two forces on one ball: your pull acts up, Earth's pull acts down.

Your pull is stronger, so the ball goes up. Draw your arrow longer.

Here's the rule. A longer arrow shows a stronger force.

To show which of two forces is stronger, draw its arrow longer.

Okay, now your turn.

Here are the toy car, the girl's box and the boy's box. Here's everything we found out.

A gentle push, and the toy car rolls a little. A stronger push, and it rolls farther and faster.

Every force has a strength. The stronger the force, the bigger the change in motion.

Now the girl's box. You can't see her push, so we draw it.

We draw a force as an arrow, called a force arrow.

A force arrow starts on the object, in its middle, and points in the direction the force acts.

Earth's pull on a falling ball: its arrow starts in the ball's middle and points straight down.

An arrow floating in the air, or pointing in the wrong direction, is drawn wrong. It does not show the force.

Now the boy's box. He pushes gently, then harder.

A longer arrow shows a stronger force. To show which of two forces is stronger, draw its arrow longer.

The arrow's length shows how strong the force is, not how big the object is.

So what was different about the two kicks? The second was a stronger push, so it made a bigger change.

How do you draw a kick you can't see? As a force arrow from the ball's middle, in the kick's direction, and longer for the harder kick.

That is the whole topic: a stronger push makes a bigger change, and an arrow shows a force's direction and strength.

Here's a boy and his dog with one rope toy.

Each of them pulls their end as hard as they can.

But the rope toy isn't going anywhere. It just stays there, between them.

Both of them are pulling. So why doesn't the rope move?

Now let's leave the game. Here's a question about you.

You're standing still on the floor. Is anything pushing or pulling you right now?

That's this topic: what happens when more than one force acts on the same thing at the same time.

Okay, so are you ready to find out why the rope toy doesn't move?

Here's a wagon on the sidewalk. A girl pulls it along.

One pull, on one wagon. That's one force on one object.

And now, the same wagon rolls along the grass. The girl is still pulling it forward.

But the grass rubs on the wheels and drags the wagon back.

So now there are two forces on the wagon.

Is that all? Earth pulls the wagon down, too.

And the ground pushes the wagon up, just as hard.

Forward, back, down and up. Four forces, on one wagon, all at the same time.

So here's the rule. More than one force can act on the same object at the same time.

The object can be moving, like the wagon, or still, like this book on a table. Either way, more than one force can act on it.

Okay, now your turn.

Here's a book resting on a table. It isn't moving.

Earth pulls the book down. So why doesn't the book fall?

Because the table pushes the book up.

The table isn't just sitting there, it pushes. So the book is still, with two forces on it.

And now, a picture hanging on a nail. Earth pulls it down, and the nail pulls it up.

Still, with two forces on it.

And now, a box on the floor. A girl pushes it from the left, and a boy pushes it from the right.

The box is still, with two pushes on it.

So here's the rule. A still object can have pushes and pulls acting on it.

Earth pulls the book down, and the table pushes it up.

Okay, now your turn.

Here's a tug of war. The green team pulls left, the orange team pulls right, and the ribbon isn't moving.

Is one team pulling harder? Here are the two pulls as arrows.

The two arrows are the same length, so the two pulls are the same strength.

When two opposite forces are the same strength, we say the forces are balanced.

But now, the green team pulls harder. Its arrow is longer.

One pull is stronger, so the forces are not balanced.

And now, the orange team pulls harder. Its arrow is the longer one, so not balanced.

And now, a girl and a boy push a box from opposite sides. Same length, same strength: the forces are balanced.

So here's the rule. Two opposite forces are balanced when they are the same strength.

When one is stronger, the forces are not balanced.

Okay, now your turn.

Here's a girl pulling a sled along the snow. It glides along at a steady speed.

She pulls the sled forward. The snow rubs on the runners and drags it back.

The two arrows are the same length, so the forces on the sled are balanced.

And the sled keeps the same speed, in the same direction.

And now, the wagon on the grass. Her pull forward and the grass's drag back are the same strength.

Balanced. The wagon keeps rolling at a steady speed.

And now, a car on a straight road. Its speed and direction aren't changing.

So the forces on the car are balanced.

So balanced doesn't mean still. This sled is moving, and the forces on it are balanced.

So here's the rule. While the forces on a moving object are balanced, it keeps the same speed and the same direction.

Okay, now your turn.

Here's the tug of war again. Both teams pull hard, and the rope isn't moving.

The two pulls are the same strength: balanced. And the ribbon stays over the mark.

And now, the book on the table. Earth pulls it down, and the table pushes it up, just as hard.

The forces on the book are balanced. The book stays still.

And now, a backpack sitting still on a chair. Earth pulls it down, and the chair pushes it up, just as hard.

The forces are balanced. The backpack stays still.

But now, someone bumps the chair away. Nothing pushes the backpack up any more.

Now only Earth's pull acts on it. The forces are not balanced, so the backpack falls.

So here's the rule. While the forces on a still object are balanced, it also keeps its motion as it is: it stays still.

Okay, now your turn.

The wagon on the grass. Her pull forward, the grass's drag back, Earth's pull down, the ground's push up. Four forces on one wagon.

More than one force can act on the same object at the same time.

Now the book on the table. It's still, but Earth pulls it down and the table pushes it up.

A still object can have pushes and pulls acting on it.

Now the tug of war. The two arrows are the same length, so the two pulls are the same strength.

Two opposite forces are balanced when they are the same strength.

When one force is stronger, the forces are not balanced.

Balanced always compares two forces. One force on its own can't be balanced.

Now the sled. The girl's pull forward and the snow's drag back are the same strength: balanced.

While the forces on a moving object are balanced, it keeps the same speed and the same direction.

And the still ribbon? Its forces are balanced too, so it stays over the mark.

While the forces on a still object are balanced, it stays still.

So why didn't the rope toy move? The boy's pull and the dog's pull were the same strength: balanced.

And when you stand still, Earth pulls you down and the floor pushes you up. Two forces, balanced.

So balanced doesn't mean still. Balanced forces leave the motion as it is.

Okay, now your turn.

Here's a boy on a skateboard, moving along a flat path at the same speed.

He pushes off with his foot, and he goes faster.

Then he drags his foot on the ground, and he goes slower.

Then his friend bumps him from the side, and off he goes in a new direction!

Faster, slower, a new direction. What decided which one happened?

Now let's look at the forces. Each time, something pushed him.

Was it how strong the push was, or which direction it acted in?

That's this topic: what happens to a moving thing when its forces are not balanced.

Okay, so are you ready to find out what makes a moving thing go faster, slower, or turn?

Here's the girl and her wagon again, on the grass, moving at the same speed.

Four forces act on it. Earth's pull down and the ground's push up stay balanced.

So watch the other two: her pull forward, and the grass's drag back. Same length: balanced, so the motion stays as it is.

But now, she pulls harder. Her arrow grows longer than the drag arrow.

The forces are not balanced any more. We call them unbalanced forces.

The stronger force acts in the direction the wagon is already moving.

So the wagon speeds up. Watch it go faster and faster.

And now, a moving cart. The boy pushes it harder, so his push is stronger than the drag, and the cart speeds up too.

So here's the rule. When the stronger force acts in the direction an object is already moving, the object speeds up.

Okay, now your turn.

Here's a boy riding his bike along a flat path, moving at the same speed.

Two forces act on the bike: his push forward from pedaling, and the drag back.

The arrows are the same length. The forces are balanced, so the speed stays the same.

But now, he keeps pedaling and squeezes the brakes. The brakes push the bike back, hard.

The push back is now stronger than the push forward. The forces are unbalanced.

The stronger force acts against the direction the bike is moving.

So the bike slows down. Watch it go slower and slower.

And now, the boy's moving cart rolls onto a thick rug. The rug drags it back harder than he pushes it, so the cart slows down too.

So here's the rule. When the stronger force acts against the direction an object is moving, the object slows down.

Okay, now your turn.

Here's a ball moving straight along the grass. A girl runs up beside it.

She kicks it from the side. Her kick is a push from the side, and nothing pushes back against it.

So the forces on the ball are unbalanced, and the ball turns. It rolls off on a new path.

It turns only while the shoe pushes it. After the kick, it rolls straight again.

And now, a toy boat, moving straight across a pond. The wind pushes it from the side.

Nothing pushes back against the wind, so the boat changes direction too.

But now, the girl kicks the ball from behind, in the direction it's already moving. It speeds up, and it keeps rolling in the same direction.

So here's the rule. When something pushes a moving object from the side, and nothing pushes back against it, the object changes direction.

Okay, now your turn.

The girl and her wagon, the boy and his bike, the ball on the grass. Here is everything we found out.

The girl's wagon is moving at the same speed. Her pull forward and the drag back are balanced, so the motion stays as it is.

Then she pulls harder, and her pull is stronger than the drag. The forces are not balanced any more.

We call forces that are not balanced unbalanced forces.

When the stronger force acts in the direction an object is already moving, the object speeds up.

Now the boy's bike is moving along. He squeezes his brakes, and the push back is stronger than the push forward.

When the stronger force acts against the direction an object is moving, the object slows down.

A ball moving along the grass slows down for the same reason: nothing pushes it forward, and the grass drags it back.

Now the ball is moving straight, and the girl kicks it from the side. Nothing pushes back against her kick.

When something pushes a moving object from the side, and nothing pushes back against it, the object changes direction.

It turns only while the push acts. Then it rolls straight again, in its new direction.

So what decided what the skateboard did? He was already moving forward. It was the direction the stronger force acted in.

Unbalanced forces can change how something moves in three ways: they can make it speed up, slow it down, or change its direction.

Balanced forces leave the motion as it is. Unbalanced forces change it.

Okay, now your turn.

Here's a big drum in a school hall. Bilal rests his hand flat on top of it.

His friend hits the drum. Boom! Bilal's hand jumps.

What did his hand feel?

Now let's go to the back of the hall. Selin stands there, a long way from the drum.

Boom! Selin hears it too. Nothing touched her, and the drum is way over there.

Between the drum and Selin, the hall looks empty. Is it?

So how did the sound get all the way to Selin's ears?

That's what this topic is about: what fills the hall, where sound comes from, and how it gets to your ear.

Okay, so are you ready to find out what Bilal's hand felt?

Here's Astrid on a hot day. She fans her face with her hands.

She feels a breeze on her cheeks. But she looks, and there's nothing there to see.

So what did she feel? She felt the air.

Her hands moved the air. The moving air reached her cheeks.

You can't see air. But you can feel it.

And now a windy day on a hill. The wind moves Finlay's hair and the flag.

Wind is air that's moving. Finlay feels it on his face.

And now Nell breathes in. Air goes in through her nose, and her chest gets bigger.

She can't see the air going in. But she can feel it.

Here's the rule: air is something real. You can't see it, but you can feel it.

Okay, now your turn.

What is air? Look across the room: you see right through it, and it looks like nothing at all.

But air is actually made of tiny pieces, far too small to see. They move around and bump into each other all the time.

Scientists call these tiny pieces particles.

When a breeze touches your face, that's countless tiny pieces of air reaching your skin.

But it's not just air. Here's a book: if we zoomed in really far, we'd see that the book is made of tiny pieces too, far too small to see.

The same for this glass of water. Zoom in really far, and it's tiny pieces too.

Here's the rule: air is made of tiny pieces far too small to see.

Okay, now your turn.

Here's a ruler on a desk. A girl holds one end down; the other end hangs over the edge.

The ruler is still. No sound.

Now she flicks the free end.

The ruler shakes back and forth, very fast. Buzz!

Shaking like this is called vibrating.

The ruler is vibrating, and it makes a sound.

And now, a drum with rice on top. A stick hits it, boom!

The rice jumps up. The drum skin is vibrating.

And now, a rubber band over a box. She plucks it, hum!

The band shakes back and forth, very fast. It's vibrating.

Now let's try it on you: hand flat on your throat, and hum.

Feel that? Something in your throat is vibrating.

But now she holds the ruler still. No shaking, no sound.

Here's the rule. Every sound is made by something vibrating.

Okay, now your turn.

Here's a drum on a field, and a boy far away.

A stick hits the drum, boom!

He hears it, but nothing touched him, so how did it reach him?

Between them is air, made of tiny pieces far too small to see.

The drum skin vibrates and shakes the tiny pieces of air next to it.

Those pieces shake the pieces next to them.

The vibration travels through the air.

It reaches his ear: he hears the drum.

Now a bell in a tower rings and vibrates.

The vibration travels through the air to a girl's ear; she hears it.

Now a dog barks behind a boy who isn't looking; its throat vibrates.

The vibration still travels through the air to his ear; he hears the bark.

Here's the rule. You hear a sound because the vibration travels through the air to your ear.

Okay, now your turn.

Here's a drum, and a tray of rice on a table right beside it.

A stick hits the drum with a boom.

The rice jumps! But the drum never touched the rice.

The drum skin vibrates, and the vibration travels through the air to the rice.

The drum's sound carries energy to the rice, and the rice jumps.

The rice is close to the drum. It jumps a lot.

Now the drum moves farther from the table. Boom!

The rice jumps less.

Now the drum moves right across the room. Boom!

The rice barely jumps.

It's the same drum and the same rice. Only the distance changed.

Here's the rule. The farther a thing is from the sound, the less it shakes.

Okay, now your turn.

Here's everything we found out.

Astrid fans her face and feels a breeze. She felt the air.

Air is something real: you cannot see it, but you can feel it.

Air is made of tiny pieces far too small to see. Scientists call them particles.

A girl flicks a ruler, and it shakes back and forth, very fast. Buzz!

Shaking back and forth very fast is called vibrating.

Every sound is made by something vibrating.

Now the drum on the field. The boy is far away, but the skin shakes the tiny pieces of air next to it, and the vibration travels through the air to his ear.

You hear a sound because the vibration travels through the air to your ear.

Now the tray of rice beside the drum. Boom! The rice jumps, though nothing touched it.

The vibration travels through the air to the rice. The drum's sound carries energy to the rice.

Close to the drum, the rice jumps a lot. Far away, it barely jumps.

The farther a thing is from the sound, the less it shakes.

So what did Bilal's hand feel? The drum skin vibrating.

And how did the boom reach Selin? The hall is full of air, and the vibration traveled through it to her ear.

That is the whole topic. Air is made of tiny pieces, and every sound is made by something vibrating.

The vibration travels through the air to your ear, and the farther a thing is from the sound, the less it shakes.

Okay, now your turn.

Here's a playground. A girl swings high on the swing.

The metal slide has stood in the sun all day. It's hot.

At the top of the slide, a boy holds a ball up high.

Down on the grass, another ball sits still, cool and low.

What do the swing, the hot slide and the held-up ball have in common?

Now let's go indoors. A lamp is on across the room, and the wall beside you is lit up.

How did anything get from the lamp to the wall?

That's this topic: what those things have, and how it gets from one thing to another.

Okay, so are you ready to find out what they have in common?

Here's a girl bouncing on her toes. She says, 'I've got lots of energy today!'

Her friend lies flat on the grass. He says, 'I'm too tired to move.'

That's how we talk every day. In science, everything has energy.

The girl has energy, and the boy lying still has energy too.

Here's a ball at the top of a hill, and the same kind of ball at the bottom.

The top ball is higher up, so it has more energy.

So things have different amounts of energy. And a moving thing, a hot thing and a high-up thing each have a different type.

A ball sitting still on the grass is a little warm, so it has energy too. It's just hard to spot.

So, here's what we've seen. Everything has energy. Things have different amounts of energy, and different types of energy.

Okay, now your turn.

Here's a playground. A girl swings on the swing.

The slide is hot from the sun, and at the top a boy holds a ball up high. Another ball sits on the grass.

Everything has energy. The swing is moving, so its energy is easy to spot.

The slide is hot, so its energy is easy to spot.

The held-up ball is high up, so its energy is easy to spot.

The ball on the grass isn't moving, hot or high up. It has energy too, but it's hard to spot.

The energy a hot thing has is called thermal energy.

The energy a high-up thing has is called gravitational energy.

So, here's what we've seen. A thing that is moving, hot or high up has energy that is easy to spot.

A hot thing has thermal energy, and a high-up thing has gravitational energy.

Okay, now your turn.

Here's a soccer ball on the grass, sitting still. A girl stands behind it.

She kicks the ball. Her kick is a push, a force.

Her foot leaves the ball, and the ball rolls on. It knocks the cone over.

The rolling ball is moving. A moving thing has energy. That energy is called kinetic energy.

Before the kick, the ball sat still. It wasn't moving, so it had no kinetic energy.

Now here's a girl sitting still on her bike at the top of a path. The bike isn't moving, so it has no kinetic energy.

She rides off down the path. Now the bike is moving, so it has kinetic energy.

Some people call kinetic energy mechanical energy. We say kinetic energy.

So, here's what we've seen. A moving thing has kinetic energy.

A thing sitting still has no kinetic energy.

Okay, now your turn.

Imagine two matching toy cars. The blue one rolls slowly, and the red one rolls fast.

Each car bumps into a box. The blue car pushes its box a little; the red car, a long way.

Which car has more energy?

Both are moving, so both have kinetic energy.

The red car gives its box more energy, so its box slides farther.

The cars match; only speed differs. The red car is faster, so it has more kinetic energy.

The blue car is slower, so it has less kinetic energy.

And now, two same-size balls. The yellow one rolls faster, so it has more kinetic energy.

And now, the same girl and bike on two days. On Tuesday she rides faster, so the bike has more kinetic energy.

Here's the rule. Of two matching things, the faster one has more kinetic energy.

Okay, now your turn.

Here's a drum and a tray of rice. The drum booms, the rice jumps, and the drum never touched it.

The drum's sound carried energy through the air to the rice.

And now, a campfire. You stand one step back, and your face warms up.

The fire's heat carries energy to your skin.

And now, a lamp across the room. The wall beside you is lit up.

The lamp's light carries energy all around the room.

Each time, the energy came from somewhere: the drum, the fire, the lamp.

And each time, something carried it: sound, heat, light.

And now, a whistle. Its sound carries energy to your ears.

Here's the rule. Sound, light and heat carry energy from one thing to another.

Finally, things that give light usually give heat too. The sun lights things up, and you can feel its heat.

Okay, now your turn.

Here's a lamp on a desk. A wire runs from it to a plug in the wall.

The switch goes on, and the lamp gives light. Where did its energy come from?

The wire is plugged into the wall. Electricity travels along the wire.

Electricity carries energy to the lamp, and the lamp gives light.

Plug out: no electricity travels along the wire, so nothing carries energy to the lamp.

And now, a toaster. Electricity carries energy along its wire, and the toaster gets hot.

And now, a fan. Electricity carries energy along its wire, and the blades move.

And now, a speaker. Electricity carries energy along its wire, and its sound carries energy to your ears.

And now, a small battery fan. Electricity carries energy along a wire from the battery too.

Here's the rule. Electricity carries energy along wires to whatever is plugged in.

Okay, now your turn.

Imagine a wind-up frog. Its key turns.

Let go, and it hops across the table.

Then it stops. Where did the energy come from, and where did it go?

Inside, the key made a spring tight. Its energy is called elastic energy.

The spring gives its elastic energy to the legs, so the frog hops.

Hop by hop, the spring gives its elastic energy away, and the frog stops.

The energy didn't disappear: the hops warmed the spring and the air, and their sound carried energy to your ears.

Now here's a toy car. Its energy comes from its battery, and a battery has chemical energy.

And now, a pan of water. The flame's heat carries energy to it, and the water warms up.

The energy came from the flame.

Here's the rule. Energy always comes from somewhere, and it always goes somewhere.

Okay, now your turn.

Here's a girl and a cart. She pushes it, and it rolls away.

Her push is a force. It acts on one thing, the cart, in one direction, forward.

Her arms leave the cart, and the push stops.

But the cart keeps rolling. It's moving, so it has kinetic energy.

The push is gone. The energy is still there.

A thing can have energy. A thing can't have a force.

And now, a hot pan. The pan has energy, its heat carries energy to the air, and there's no force in this story.

And now, a ball held high. The ball has energy, and Earth's pull on it is a force.

Here's the rule. A force acts on one thing, in one direction.

A thing can have energy, but a thing can't have a force.

Okay, now your turn.

Here's everything we found out about energy: what has it, and how it moves.

Everything has energy. Things have different amounts of energy, and different types of energy.

A thing that is moving, hot or high up has energy that is easy to spot. A hot thing has thermal energy, and a high-up thing has gravitational energy.

A moving thing has kinetic energy. A thing sitting still has no kinetic energy.

Of two matching things, the faster one has more kinetic energy.

Sound, light and heat carry energy from one thing to another. Things that give light usually give heat too.

Electricity carries energy along wires to whatever is plugged in.

Energy always comes from somewhere, and it always goes somewhere. A wind-up frog's hops come from its spring's elastic energy.

A force acts on one thing, in one direction. A thing can have energy, but a thing cannot have a force.

A push or pull, sound, light, heat and electricity are all ways of transferring energy. A force is a way of transferring energy, but a force is not energy.

Okay, now your turn.

Here's a girl in a tent at night. A flashlight on the floor points at the wall. She makes a rabbit shape with her hand in front of it.

A rabbit shadow appears on the tent wall. Why is it on that side?

Now she switches the flashlight off. Everything goes black.

She holds her hand in front of her face, eyes wide open. But she can't see it at all!

Why not? Where did the light go, and why can't she see without it?

That's this topic: where light comes from, how it travels, and why you need it to see.

Okay, so are you ready to find out why you can't see in the dark?

Here's a bedroom at night. The lamp is off, and you can hardly see the book.

Now the lamp comes on. The book is bright.

So where does the light come from? From the lamp.

The lamp is the light source. The book is lit up.

And now, a flashlight. A boy points it at a wall.

Where does the light come from? From the flashlight.

The flashlight is the light source.

And now, a sunny playground.

Where does the light come from? From the Sun.

The Sun is the light source.

But now, look at the white page under the lamp. It's very bright.

Does the page make light? No.

Light from the lamp lands on it. The page is lit up, not a light source.

Here's the rule. A light source makes light.

Light lands on everything else.

Okay, now your turn.

Here's a dusty attic. A girl's flashlight comes on.

Look at the light in the dust. It makes a straight beam, from the flashlight to the wall.

So how does light travel? In straight lines.

Each line goes straight until it hits the wall. There, the wall is lit up.

And now, a dark room with thick curtains. Sunlight comes through a small gap.

The light makes a straight stripe across the floor.

And now, a lamp and a long straight tube. A boy looks through the tube.

Light from the lamp goes straight down the tube. He sees the lamp.

But now, the tube is bent. He looks again, and sees nothing.

The light hits the inside of the tube. Light can't turn a corner.

Here's the rule. Light travels in straight lines, until it hits something.

Okay, now your turn.

Here's a flashlight pointing at a wall. A hand goes in front of it.

A dark hand shape appears on the wall. That's a shadow.

Light travels in straight lines. Some lines hit the hand and stop.

The other lines miss the hand and reach the wall.

Behind the hand, no light reaches the wall. That's the shadow.

And now, a ball. The flashlight is on the left.

The ball blocks the light. The shadow is on the right, away from it.

Now the flashlight moves to the right. The shadow is on the left, away from it.

Now the flashlight is above. The shadow is under the ball, away from it.

But now, the ball is gone. Nothing blocks the light, so there's no shadow.

Here's the rule. An object blocks the light.

Its shadow is on the side away from the light source.

Okay, now your turn.

Here's a big box with a peephole. Inside sits a toy dinosaur, and a lamp is on above it.

You look through the peephole. You see the dinosaur.

Now the lid closes. You look again, and you see nothing.

Your eyes are the same. So why?

Lid open: light from the lamp lands on the dinosaur. Then light comes from the dinosaur to your eye.

Light from the dinosaur reaches your eye. So you see it.

Lid closed: no light gets in. No light comes from the dinosaur to your eye.

So you see nothing.

And now, a deep cave with no light at all. A girl waits an hour.

She still sees nothing.

Her eyes are open. But no light reaches them.

Here's the rule. You see something only when light from it reaches your eye.

Okay, now your turn.

The tent, the rabbit shadow, and the hand she couldn't see. Here is everything we found out.

A lamp lights up a book. The light comes from the lamp.

Light comes from a light source, like the Sun, a lamp or a flashlight.

The book is lit up. It is not a light source.

A flashlight beam in the dust is straight.

Light travels in straight lines, until it hits something.

Light can't turn a corner. Through a bent tube, you see nothing.

Now the hand in front of the flashlight. The hand blocks some of the light.

Behind the hand, no light reaches the wall. That dark place is the shadow.

An object blocks the light. Its shadow is on the side away from the light source.

Now the box with the peephole. Lid open, light from the dinosaur reaches your eye, and you see it.

Lid closed, no light reaches your eye, and you see nothing.

You see something only when light from it reaches your eye.

So, the rabbit. Her hand blocked the flashlight's light, and its shadow was on the tent wall, away from the flashlight.

And with the flashlight off, no light reached her eyes. That's why she couldn't see her hand.

That is the whole topic: light comes from a light source, travels in straight lines, makes shadows, and has to reach your eye.

Okay, now your turn.

Here's a swimming pool on a hot, sunny day. Mirela is about to jump in.

The Sun sparkles on the water. It's so bright it hurts her eyes.

She jumps in and looks down. Her legs look short and bent!

Now let's go to the poolside. Mirela sits on the black mat. Ouch, it's hot!

The white towel right beside it is cool.

The same Sun shines on both. So why is the black mat so hot?

And why do her legs look bent? And why does the pool sparkle?

That's this topic: what light does when it hits something.

Okay, so are you ready to find out why the black mat is so hot?

Here's a dark room. A mirror lies flat on a table, and a flashlight above points down at it.

A bright spot appears high on the wall. But the flashlight isn't pointing there!

So how did light get there? The light travels straight down to the mirror.

It hits the mirror and bounces off. Then it travels straight again, up to the wall.

Light bouncing off a thing is called reflection.

And now, the flashlight points up at a white wall. The light bounces off the wall too.

It travels straight again, up to the ceiling. Not just mirrors bounce light off.

And now, a red book under a lamp. Light lands on the book and bounces off.

Some of it reaches your eye. That's how you see the book.

Here's the rule: light bounces off the things it hits. This is called reflection.

Okay, now your turn.

Here's a cat sitting in front of a mirror on the wall. Look at the mirror, and you see the cat in it.

But behind the mirror is only the wall. So where does the cat in the mirror come from?

Light in the room lands on the cat and bounces off it.

Some of that light travels to the mirror. It bounces off the mirror to your eye.

So you see a picture of the cat. There's no cat behind the mirror.

And now, the same mirror in a room with no light at all.

You look at the mirror. You see nothing.

No light lands on the mirror, so no light bounces off it. A mirror doesn't make light.

Here's the rule: the picture in a mirror is light that bounced off it to your eye.

Okay, now your turn.

Here's a straw in a glass of water. Look down: where it goes into the water, it looks bent!

Out of the water, the straw is straight. So why did it look bent?

Here's a tank of water in a dark room. A flashlight shines a beam into it.

In the air, the beam is straight. Where it goes into the water, it changes direction.

Back at the glass: light from the straw's bottom travels up through the water.

Where it leaves the water, it changes direction, then reaches your eye.

So the straw's bottom looks higher up than it is.

The straw isn't bent. The light changed direction.

But now, the glass is empty. The light doesn't change direction, and the straw looks straight.

Here's the rule: light changes direction when it goes from one see-through material into another. This is called refraction.

Okay, now your turn.

Here's a sunny day. Two T-shirts hang on a washing line, a black one and a white one.

Touch the black shirt. It's warm!

Touch the white shirt. It's only a little warm.

The same Sun shines on both. So why is the black shirt warmer?

Sunlight lands on the black shirt. Most of the light soaks in.

It doesn't bounce off, and it doesn't go through. The light that soaks in warms the shirt.

Light soaking into a thing is called absorption.

A little light still bounces off the black shirt. That's how you see it.

And now, the white shirt. Most of the light bounces off it.

Only a little of the light soaks in, so it stays cooler.

Here's the rule: a dark surface soaks up most of the light that lands on it. This is called absorption.

Okay, now your turn.

Here's a pond on a sunny afternoon. The Sun sparkles on the water.

A stick in the shallow water looks bent. And the dark rock by the pond is hot.

Light hit the water, the stick and the rock. Did it do the same thing each time?

Let's sort it. When light bounces off, we say it was reflected.

When light changes direction going into or out of water or glass, we say it was refracted.

When light soaks in, we say it was absorbed.

So, the pond: the light bounced off the water. It was reflected.

The stick: light from it changed direction as it left the water. It was refracted.

The rock: most of the light soaked in. It was absorbed.

Here's the rule: when light hits something, it bounces off, changes direction as it goes through, or soaks in.

Reflected, refracted, or absorbed.

Okay, now your turn.

A flashlight points at a mirror. The light hits the mirror and bounces off, up to the wall.

Light bounces off the things it hits. This is called reflection.

Not just mirrors: light bounces off a white wall, a book, a face. That's how you see them.

The picture in a mirror is light that bounced off it to your eye. A mirror doesn't make light.

A beam of light goes from the air into water. Where it goes in, it changes direction.

Light changes direction when it goes from one see-through material into another. This is called refraction.

That's why a straw in a glass of water looks bent. The straw is straight. The light changed direction.

Sunlight lands on a black shirt. Most of the light soaks in, and the shirt gets warm.

A dark surface soaks up most of the light that lands on it. This is called absorption.

A white shirt bounces most of the light off, so it stays cooler.

When light hits something, it bounces off, changes direction as it goes through, or soaks in.

Bounced off: reflected. Changed direction: refracted. Soaked in: absorbed.

So, the pool. Sunlight bounced off the water to Mirela's eyes. It was reflected.

Her legs: light from them changed direction where it left the water. They only looked bent. It was refracted.

And the black mat: most of the sunlight soaked in and warmed it. It was absorbed.

That is the whole topic: light bounces off, changes direction, or soaks in. Reflected, refracted, absorbed.

Okay, now your turn.

Here's a cat asleep on a windowsill, in the sunshine. The sill is warm, but nothing hot has touched it.

Now let's go indoors at night. A lamp has been on all evening. A boy switches it off, brushes the bulb by accident, and ouch, it's hot!

The lamp is for giving light. So why is the bulb hot?

And now let's step outside on a frosty morning. A girl's hands are cold. She rubs them together, and they warm up.

Three warm things. Where did the warmth come from each time?

That's this topic: light, and the warmth that comes with it.

Okay, so are you ready to find out why the sunny windowsill is warm?

Here's a desk lamp with an old glass bulb. It's been on for an hour.

Someone brushes the bulb by accident. Ouch, it's hot!

So, does the lamp give light? Yes.

Is it warm too? Yes.

Now the lamp is off. No light comes from it, and the bulb is cool.

And now, a candle: does it give light? Yes.

Is it warm too? Yes.

And now, a campfire: does it give light? Yes.

Is it warm too? Yes.

And now, the Sun: does it give light? Yes.

Is it warm too? Yes, the Sun is very hot.

But now, a glow stick: does it give light? Yes.

Is it warm too? No, it stays cool.

Here's the rule. Something that gives light is usually warm too.

Okay, now your turn.

Here's a bike. It's stood in the sunshine all afternoon.

Someone sits on the seat, and ouch, it's hot! So how did it get warm?

The Sun's light travels to the bike and lands on the seat.

Light carries energy. The Sun's light carries energy to the seat, and the seat warms up.

Now let's put the same bike under a tree.

The light lands on the leaves. The seat is in the shade: the Sun's light does not reach it, so the seat stays cool.

And now, a lamp pointing at a stone, for an hour.

The lamp's light carries energy to the stone, and the stone warms up.

Here's the rule: light carries energy from its source to whatever it lands on, and where light lands, the thing warms up.

Okay, now your turn.

Here's a cold morning. A girl's hands are cold.

She rubs them together, fast, and now they're warm! So where did the warmth come from?

Her hands were moving. A moving thing has kinetic energy.

The moving hands gave some of that energy to the skin where they rub. So the hands got warmer.

But now, she presses her cold hands together and holds them still.

Nothing moves, and nothing warms up. Her hands stay cold.

And now, an eraser on paper. She rubs it back and forth, fast.

The eraser is warmer. The paper is warmer too.

And now, a stick rubbed on a log. Both get warmer.

Here's the rule. When two things rub together, both get warmer.

Okay, now your turn.

The warm windowsill, the hot bulb, and the cold hands rubbed warm. Here is everything we found out.

The lamp gives light, and its bulb is hot. The candle gives light, and its flame is warm.

Something that gives light is usually warm too.

Usually, not always. The glow stick gives light and stays cool.

Now the bike seat in the sunshine. The Sun's light travels to the seat and lands on it.

Light carries energy from its source to whatever it lands on.

Where light lands, the thing warms up. So the seat warms up.

Under the tree the seat is in the shade. The Sun's light does not reach it, so it stays cool.

Now the cold hands. She rubs them, and they warm up.

Her hands were moving, and a moving thing has kinetic energy. The moving hands gave some of that energy to the skin where they rub, so they got warmer.

When two things rub together, both get warmer.

So, the windowsill. The Sun's light carried energy to the sill, and the sill warmed up. The cat found the warm spot.

And the hands: they moved, and the moving hands gave some of their energy to the skin, so they got warmer.

That is the whole topic: something that gives light is usually warm too, light carries energy to whatever it lands on, and when two things rub together, both get warmer.

Okay, now your turn.

Here's a kitchen at night.

A bag of flour lies on its side, and white powder covers the floor. In the powder: footprints.

In walks a detective. She looks. She listens. She sniffs.

A faucet drips. Something smells of oranges. The footprints are small, with long toes.

'A raccoon did it!' she says. But did she see a raccoon, or does she just think so?

Now let's look at the table. A key, a feather, a button, an orange peel: twenty clues in a jumble.

How would you sort all those clues?

That's what this topic is about: finding out about things, describing them, and sorting them.

Okay, so are you ready to solve the case?

Here's a can of soda on a table. Imagine your eyes are shut.

Someone opens the can. Fizz!

You didn't see it, but you heard it. You noticed something with your ears.

Something you noticed is called an observation.

Now your eyes are open, and here's the soda in a glass. It's brown.

Your eyes told you that. That's an observation.

You touch the can. It's cold, and it's smooth.

Your hands told you that. That's an observation.

You sniff. The soda smells sweet.

Your nose told you that. That's an observation.

Write down what you noticed: brown, cold, smooth, fizzed, smells sweet.

Here's the rule. You can observe with your eyes, ears, hands and nose.

When you notice something with them, what you noticed is an observation.

Finally: in science, we don't taste things to observe them. Some aren't safe to taste.

Okay, now your turn.

Here's a puddle in the playground in the morning. After lunch, it's smaller.

Kirra says two things.

'The puddle is smaller than this morning.' 'The water soaked into the ground.'

Did she see that? Yes: she saw the puddle this morning, and she sees it now.

So that's an observation.

Did she see the water soak into the ground? No, nobody saw that.

So that's an idea about it. It might be right or wrong.

And now, a plate that had a cookie on it. Dad says, 'The plate is empty.'

Did he see that? Yes, so that's an observation.

But, 'The dog ate the cookie.' Did he see that?

No, so that's an idea about it.

Here's the rule. Ask: did you see it, hear it, feel it or smell it?

Yes: it's an observation. No: it's an idea about it.

Okay, now your turn.

Imagine you left your water bottle at the park. Your friend goes back for it.

You say, 'It's my bottle.' But there are lots of bottles.

So you say more: 'It's blue and tall, smooth, with a black lid.'

Now your friend finds it.

Each thing you said is a property.

A property is something you can say about an object.

And now, a pebble. It's gray: that's its color.

It's round: that's its shape. It's small: that's its size.

It's smooth and hard: that's how it feels.

But, 'A bird dropped this pebble here.' Is that a property?

No, that's the pebble's story, not what it's like. It's still gray and smooth.

Here's the rule. A property is something you can say about an object: its color, shape, size, or how it feels.

You find properties by looking and feeling.

Okay, now your turn.

Here are eight buttons in a jumble. Some buttons are red and some are blue, some are big and some are small.

Let's sort them by color.

The red buttons go together, and the blue buttons go together.

Every button in this group is red. Every button in that group is blue.

The buttons are sorted by color.

But now, one blue button sits in the red group.

Is this group sorted by color? No, one button is a different color.

The blue button goes back. Now they're sorted by color again.

And now, the same buttons, sorted by size. The big ones go together, and the small ones go together.

A red button and a blue button sit together. That's fine, they're the same size.

Here's the rule. To sort by a property, put the objects that are the same in that property together.

Okay, now your turn.

Here are six white shells on a tray. Let's sort them into two groups.

Sort them by color? Every shell is white.

They all go in one group. One group isn't a sort.

Sort them by size? Some shells are big and some are small.

The big shells go together, and the small shells go together. Two groups!

Size can sort these shells. Color can't.

And now, six blue socks, all the same length. Some socks are fluffy and some are smooth.

Color can't sort them. Length can't sort them.

How they feel can: fluffy socks together, smooth socks together.

Here's the rule. To choose a property to sort by, pick one that's different from object to object.

A property that's the same for every object puts them all in one group.

Okay, now your turn.

Suppose you have three pencils on your desk. Let's put them in order from shortest to longest.

The shortest pencil goes first.

The next shortest goes next. And the longest goes last.

Now they're in a line, from shortest to longest. They're in order by length.

And now, three cups. The shortest goes first, and the tallest goes last.

And now, three stones. You feel each one.

The smoothest goes first, and the roughest goes last.

But now, three cups: red, blue and yellow. Can you put them in order by color?

No, red isn't more than blue. A color has no least and no most.

Here's the rule. To put objects in order, line them up from the least of a property to the most.

Sorting makes groups. Ordering makes a line.

Okay, now your turn.

The can of soda, the puddle, the water bottle, the buttons, the pencils. Here's everything we found out.

With your eyes shut, you heard the can fizz. That was an observation.

You can observe with your eyes, ears, hands and nose.

An observation is something you noticed with your eyes, ears, hands or nose.

Kirra said the puddle was smaller than this morning. She saw that, so it was an observation.

She said the water soaked into the ground. Nobody saw that, so it was an idea about it.

An idea about it is something you think is true, but did not observe.

The bottle was blue, tall and smooth, with a black lid. Each of those is a property.

A property is something you can say about an object: its color, its shape, its size, or how it feels.

The buttons went into a red group and a blue group. To sort by a property, put the objects that are the same in that property together.

The white shells couldn't be sorted by color. To choose a property to sort by, pick one that is different from object to object.

The pencils went in a line, shortest to longest. To put objects in order, line them up from the least of a property to the most.

Sorting makes groups. Ordering makes a line.

That is the whole topic: observe it, describe it, sort it.

Okay, now your turn.

It's a hot afternoon at the pool. Farah says it's really hot. Musa says it's super hot.

But how hot is it? On the wall, a thermometer holds the answer, as a number.

Now let's go to the kitchen. Farah wants to know how much apple she has. Not 'a bit', but a number.

And out in the yard, two teams measure the same puddle. They get two different numbers. Who's right?

That's what this topic is about: the tools that turn 'how hot', 'how much stuff' and 'how much liquid' into numbers, and what to do when two teams disagree.

Okay, so are you ready to put some numbers on it?

Here's a thermometer on a porch. The top of the red liquid sits one small mark above the seventy.

Farah says seventy-one, Musa says seventy-two. Who's right?

You've read a ruler before. From ten to twenty there are ten spaces.

Count up in ones: eleven, twelve, on to twenty. Ten ones land on twenty, so each mark is worth one.

Now the thermometer. From seventy to eighty there are five spaces.

Count up in ones: seventy-one, seventy-two, seventy-three, seventy-four, seventy-five. That lands on seventy-five, not eighty.

So these marks aren't worth one.

Count up in twos: seventy-two, seventy-four, seventy-six, seventy-eight, eighty. That lands on eighty.

Ten divided by five is two: each mark is worth two.

Here's the rule: count the spaces, then count up to land on the next number. That's what one mark is worth.

One mark above seventy is seventy-two. Musa's right.

Okay, now your turn.

Here are four tools' marks: a ruler, a thermometer, a jug and a timer.

Farah says every small mark is worth two, like the thermometer's. Is she right?

The ruler has ten spaces from ten to twenty. Ten divided by ten is one, so each mark is worth one.

The thermometer has five spaces from seventy to eighty. Ten divided by five is two.

The jug has five spaces from zero to fifty. Fifty divided by five is ten.

Count up: ten, twenty, thirty, forty, fifty. Each mark is worth ten.

The timer has two spaces from zero to ten. Ten divided by two is five.

Count up: five, ten. Each mark is worth five.

So, tools have different marks: a mark can be worth 1, 2, 5 or 10.

On a new tool, count the spaces, then count up.

Farah's not right.

Okay, now your turn.

Imagine a hot summer day. Grandpa calls, 'How hot is it?'

Here's the thermometer by the back door. The red liquid's high up.

A thermometer measures how warm or cold something is: its temperature.

Its numbers are called degrees Fahrenheit.

To read it, find the top of the red liquid.

Next, read the number just below the top. Ninety.

Now, what is one mark worth? Ninety to one hundred is five spaces: ten divided by five is two.

Then count up in twos: ninety-two, ninety-four, ninety-six.

Ninety-six degrees Fahrenheit. It's a hot day.

Now let's imagine a cold morning. The top lines up with the thirty: nothing to count up.

It reads thirty degrees Fahrenheit.

Here's the rule. Find the top of the red liquid, read the number just below it, work out what one mark is worth, then count up.

You call back: ninety-six degrees!

Okay, now your turn.

Here's the same thermometer. Look closely: it has numbers on both sides.

On the left, the liquid's top is at sixty-eight. On the right, it's at twenty.

Can two numbers name one temperature?

The left numbers are degrees Fahrenheit. The right numbers are called degrees Celsius.

People in the US use Fahrenheit for the weather. Scientists everywhere use Celsius.

So sixty-eight Fahrenheit and twenty Celsius are one temperature.

Read the Celsius side the same way: find the top, read the number just below.

From twenty to thirty, ten spaces. Ten divided by ten is one, so each mark is worth one.

Now imagine a thermometer in a classroom. The top sits four marks above the twenty.

Count up in ones: twenty-one, twenty-two, twenty-three, twenty-four. Twenty-four degrees Celsius.

Here's the rule: on the Celsius side, find the top, read the number below, count up in ones.

Okay, now your turn.

Here's a digital scale. Its pan is empty, and its display reads zero.

Farah puts an apple on the pan. The numbers change, then stop at one hundred fifty.

An apple is made of stuff. How much stuff is in a thing, we call its mass.

A digital scale measures mass in grams. That's the g.

So the apple's mass is one hundred fifty grams.

Now the apple comes off, and an orange goes on. The numbers stop at two hundred.

Two hundred is more than one hundred fifty, so the orange has more mass.

To use the scale, first check that the empty scale reads zero.

Next, put the thing on the pan.

When the numbers stop changing, read the number and the g.

Here's the rule. Check the empty scale reads zero, put the thing on, and read the number when it stops changing.

Okay, now your turn.

Kenji pours some water into a tall glass tube with marks. How much is that?

How much space a liquid fills, we call its volume.

This tube is called a graduated cylinder. It measures volume in milliliters.

To read it, find the top of the water: read where the water lies.

Next, read the number just below: eighty exactly, so eighty milliliters.

Now imagine less water. Look a little closer.

The water curves up a little at the glass. When it does, read from the bottom of the curve.

Thirty to forty is five spaces: ten divided by five is two, so each mark is worth two.

Count up in twos: thirty-two, thirty-four. Thirty-four milliliters.

Here's the rule. Find the top of the water, or the bottom of its curve. Read the number below, work out what one mark is worth, then count up.

Okay, now your turn.

Imagine a class picnic: a jug of lemonade, a cup, and a watermelon.

Chloe has three questions. How warm is the lemonade, how much is in her cup, and what's the watermelon's mass?

Each needs a different tool. Which one?

First, ask what you want to know.

How warm is the lemonade? That's a temperature question, and a thermometer measures temperature.

How much lemonade is in her cup? That's a volume question, and a graduated cylinder measures a liquid's volume.

What's the watermelon's mass? That's a mass question, and a scale measures mass.

And how long is the picnic table? That's a length question, and a ruler measures length.

Same lemonade, two questions, two tools. The question decides the tool.

Here's the rule: first ask what you want to know. Temperature, a thermometer; mass, a scale; a liquid's volume, a graduated cylinder; length, a ruler.

Okay, now your turn.

Two teams measure the air outside: Team Red's thermometer on the sunny wall, Team Blue's under a shady tree.

Team Red reads ninety. Team Blue reads seventy-six.

Team Red says Team Blue made a mistake. Did they?

Different numbers? Ask one question: did they measure in the same way?

One sat in the sun and one in the shade, so no, they didn't.

The difference comes from how they measured: the sun warmed Team Red's thermometer.

Now consider two teams reading the same cylinder. Team Green says forty-three, Team Yellow forty-six.

Did they measure in the same way? Yes, so someone may have made a mistake.

They read it again: three marks above forty, each worth two, is forty-six. Team Green counted marks as one.

Here's the rule. Did they measure in the same way?

If not, that's the reason. If they did, measure again.

Okay, now your turn.

Thermometer, scale, cylinder. Here's everything we found out.

First, the marks. The small marks between two numbers are not always worth 1. Count the spaces, then count up to land on the next number.

Five spaces from seventy to eighty: ten divided by five is two, so each mark is worth two. A mark can be worth 1, 2, 5 or 10.

To read a thermometer, find the top of the red liquid and read the number just below it. Work out what one mark is worth, then count up.

Ninety, then ninety-two, ninety-four, ninety-six. Ninety-six degrees Fahrenheit.

The same thermometer has a Celsius side. Fahrenheit is used for the weather in the US and Celsius by scientists everywhere.

Sixty-eight degrees Fahrenheit and twenty degrees Celsius are one temperature. On the Celsius side each mark is worth one.

Now the scale. A digital scale measures mass in grams. Check the empty scale reads zero, put the thing on, and read the number when it stops changing.

Now the cylinder. A graduated cylinder measures a liquid's volume in milliliters. Find the top of the water; if the water curves, read from the bottom of the curve. Read the number below and count up.

Which tool? To pick the tool, first ask what you want to know. Temperature, a thermometer. Mass, a scale. A liquid's volume, a graduated cylinder. Length, a ruler.

And when two teams disagree? Two teams can get two different numbers without anyone making a mistake. Ask: did they measure in the same way?

Sun and shade: the numbers differ because of how they measured. Same water, same cylinder, different numbers: measure again.

That's the whole topic: measuring tools, and how to read them.

Okay, now your turn.

Here's a small stone and a big sponge. Which one has more stuff in it?

Amira says the sponge, because it's bigger. Is she right?

Now let's drop a marble and a bolt into two glasses of water. The water moves up in both. Which one takes up more space?

And now let's go to two bowls of water. Perla's left hand says warm. Her right hand says cool. About the same bowl!

That's what this topic is about: deciding which one has more, more stuff, more space, or which is warmer, by measuring, not guessing.

Okay, so are you ready to find out which has more?

Here's a small stone and a big sponge. Which one has more stuff in it?

Amira says the sponge, because it's bigger. Is she right?

A pan balance compares mass: how much stuff a thing has.

With nothing on the pans, the beam is level.

Now the stone goes on one pan, and the sponge on the other.

The stone's pan hangs lower, and the lower pan holds more mass.

So the stone has more mass. Amira wasn't right.

And now a pear and an orange. The pans hang level: the same mass.

Here's a digital scale. The stone goes on: sixty grams.

The stone comes off, the sponge goes on: twenty grams.

Sixty is bigger, so the stone has more mass.

The rule: the pan that hangs lower holds the object with more mass.

A bigger object does not always have more mass.

Okay, now your turn.

Here are two cylinders, with water at fifty in both.

Liv drops a marble into one and a bolt into the other. Each sinks, and the water moves up.

The balance showed the bolt has more mass. Does it take up more space?

Every object takes up a space. The marble takes up space at the bottom, so the water can't be there and moves up.

Now look at the two levels. The marble's water is higher, so the marble takes up more space.

The bolt has more mass, but the marble takes up more space.

And now a big pebble and a small one. The big pebble's water is higher: more space.

And now a die and a domino. The same level means the same space.

Here's the rule. The water rises higher for the object that takes up more space.

Okay, now your turn.

Here are two bowls of water. Perla puts her left hand in the cold one, her right in the warm one.

Then both hands go into one bowl. Left says warm, right says cool.

Hands can be wrong about which is warmer. A thermometer decides.

Now consider cold tap water and warm tap water, a thermometer in each.

Read the Fahrenheit side on both: fifty-four, and one hundred four.

One hundred four is bigger, so the warm tap's is warmer.

Now two cups both read sixty-six. The same number, the same temperature.

And now Perla reads cup A on the Fahrenheit side, cup B on the Celsius side.

Different sides, so the bigger number tells her nothing. Cup B's Fahrenheit side reads eighty-six: cup B is warmer.

Here's the rule. Read the same side on both thermometers, and the bigger number is the warmer one.

Okay, now your turn.

The stone and the sponge, the marble and the bolt, the two taps. Here's everything we found out.

First, the pan balance. Put one object on each pan. The pan that hangs lower holds the object with more mass.

The stone's pan hung lower, so the small stone had more mass than the big sponge. A bigger object does not always have more mass.

Level pans mean the same mass.

A digital scale shows the mass in grams. The stone on: sixty. The stone off, the sponge on: twenty. Sixty is bigger, so the stone has more mass.

Next, space. An object takes up a space that nothing else can be in at the same time.

That's why the water moved up. The marble took up space, and the water couldn't be in that space.

Two cylinders, the same water to start, one object in each. The water rises higher for the object that takes up more space.

The marble's water was higher, so the marble took up more space, even though the bolt had more mass.

Last, warmth. Your hands can be wrong about which is warmer. Perla's two hands gave two answers about one bowl.

So put a thermometer in each. Read the same side on both thermometers, and the bigger number is the warmer one.

Different sides? Then the bigger number tells you nothing. Same side first.

That's the whole topic: which has more, decided by a measurement.

Okay, now your turn.

Here's a huge pumpkin and a tiny grape, and a tub of water. Which one will float?

The huge pumpkin floats. The tiny grape sinks. How can that be?

Now let's look at two bottle caps, the same shape. A magnet comes close. It takes one and leaves the other. Why?

And now let's make a brick out of mud. When it dries, it cracks. Mix in some straw, and it holds. What changed?

That's what this topic is about: testing what stuff does, sinks or floats, sticks to a magnet or not, and picking the right stuff for the job.

Okay, so are you ready to test some stuff?

Here's a big wooden log and a small steel nail, and a tank of water.

Fidel says the log will sink, it's so big, and the nail will float, it's so small. Is he right?

Here's the test. Lower the object into the water, and let go.

The log stays at the top. The log floats.

Now the nail: it goes down to the bottom. The nail sinks.

The big log floats, and the small nail sinks. Fidel wasn't right.

You can't tell by looking. You have to test it.

Fidel writes what happened in a table: log, floats. Nail, sinks.

And now a stone. It goes to the bottom: sinks.

And now a candle stub. It stays at the top, most of it under: floats.

Here's the rule: lower it in and let go. To the bottom, it sinks; stays at the top, it floats.

Okay, now your turn.

Here are two paperclips, the same shape and size: one steel, one plastic.

A magnet hangs just above each one. Which one will it pull?

The steel paperclip jumps up. The magnet pulls it.

The plastic paperclip stays where it is. The magnet doesn't pull it.

The stuff an object is made of is called its material. Steel and plastic are materials.

A magnet pulls steel, so steel is magnetic. It doesn't pull plastic, so plastic is not magnetic.

And now a steel nail. It jumps up: magnetic.

And now a wooden block. It stays: not magnetic.

And now two cans: the steel can jumps up. The aluminum can stays, even though it's metal.

So Tomi sorts them into two groups: magnetic, and not magnetic.

Here's the rule: bring a magnet close to each object, and if the magnet pulls it, it is magnetic.

Okay, now your turn.

Yoel presses wet sand into a brick and dries it. Then it falls onto the path.

It breaks into bits. What could he add so the brick holds together?

Yoel makes three bricks the same size: sand only, clay only, and sand and clay.

All three dry for two days. Only what they're made of differs.

That's a fair test. Now each brick falls from the same height.

The sand brick breaks into bits, the clay brick cracks, and the sand-and-clay brick stays whole.

A brick that stays whole when it falls is strong. The mixed brick is strong.

And now flour and water. Flour alone falls apart; water alone spreads out flat.

Mixed, they make dough, and dough holds its shape.

Here's the rule: two materials mixed together can do a job better than either alone. Test each one the same way.

Okay, now your turn.

Effie runs across the kitchen in her socks. She slips!

She puts on her sneakers and runs again. No slipping, so why?

A sole has a job: to grip the floor. So it needs a material that's grippy.

Rubber is grippy. So rubber suits a sole.

But now a glass sole. Glass is smooth and slippery, so glass doesn't suit a sole.

And now a window, whose job is to let you see out. Glass is see-through, so glass suits a window.

And now a raincoat, whose job is to keep the rain off. Plastic keeps water out, so plastic suits it.

But paper soaks up water. So paper doesn't suit a raincoat.

Here's the rule. Name the property the job needs, and say the material has it.

Okay, now your turn.

The log and the nail, the two paperclips, the three bricks, the rubber sole. Here's everything we found out.

First, the water test. Lower the object in and let go. If it goes to the bottom, it sinks. If it stays at the top, it floats.

The big log floated and the small nail sank. You cannot tell by looking whether a thing sinks or floats. You test it.

Write down what happened, one row for each object.

Next, the magnet test. The stuff an object is made of is called its material.

A thing a magnet pulls is magnetic. Steel is magnetic; plastic, wood and aluminum are not.

Bring a magnet close to each object. If the magnet pulls it, it is magnetic. If not, it is not magnetic.

Then the bricks. Two materials mixed together can do a job better than either one alone.

Sand and clay together stayed whole. A brick that stays whole when it falls is strong.

Test each one the same way. A fair test changes one thing only.

Last, choosing a material. To say why a material suits a job, name the property the job needs, and say the material has it.

A sole needs to grip. Rubber is grippy. So rubber suits a sole.

That's the whole topic: test what the stuff does, then pick the right stuff for the job.

Okay, now your turn.

Here's Pim with a blown-up balloon. She wants to put it in the gap in the cupboard.

It won't fit. But the balloon looks so light and empty. What is stopping it?

Now let's watch Tamsin pour a bowl of sand into a jar. It pours, just like juice.

So is sand a liquid? And what about honey, which pours so slowly?

That's what this topic is about: what stuff is made of, what air does, and whether each kind of stuff is a solid, a liquid or a gas.

Okay, so are you ready to find out what air, honey and sand really are?

Air is made of tiny pieces far too small to see. So is a book, and so is the water in a glass.

Now here's a brick wall, a wooden chair, and you. Are they made of tiny pieces too?

Yes, the wall is made of tiny pieces, each far too small to see. So is the chair, and so are you.

Stuff of every kind, the book, the wall, the water, the air, is called matter.

Every kind of matter is made of tiny pieces far too small to see.

So why can you see the book? The book's pieces are packed very close together.

Think of ants. One ant is hard to see, but hundreds together make a dark patch you can see.

Here's the rule: every kind of matter is made of tiny pieces. Each piece is far too small to see.

Okay, now your turn.

Here's Pim with a blown-up balloon. She wants to put it in the gap in the cupboard.

She pushes, but it doesn't fit. The balloon looks so light and empty, so why won't it fit?

The balloon isn't empty. It's full of air.

The air takes up the space inside the balloon. So the balloon takes up space, and it's too big for the gap.

Now Pim unties the balloon. The air comes out, and the balloon goes small.

Now it fits in the gap easily. Only one thing changed: the air is gone.

Air is all around you, but you never notice it taking up space. In a balloon, you can.

Here's the rule: air takes up space. When the air comes out, the balloon goes small.

Okay, now your turn.

Here's Huw with a long thin balloon. He blows air into it.

The air goes right to the tip, and to every part in between. Does air have a shape of its own?

Air is a kind of matter called a gas. There are other gases too, like the gas in soda bubbles.

Watch the long balloon. The air spreads out to fill all of it.

And now a round balloon. The air spreads out to fill the whole balloon.

And now a bike tire. The air spreads out to fill the whole tire.

But now Huw pours water into the long balloon. It sits in the bottom part, with a flat top.

Water doesn't spread out to fill all the space, so water isn't a gas.

Here's the rule: a gas spreads out to fill all the space it is given. Air is a gas.

Okay, now your turn.

Here's Winnie with a pitcher of juice. She pours some into a tall glass.

Then some into a wide bowl, and some into a square box. What shape is it?

In the tall glass, the juice is tall and thin. In the wide bowl, it's wide and flat.

In the square box, it's square. The juice takes the shape of whatever holds it.

Juice is a kind of matter called a liquid.

And now honey. It pours slowly, but it still takes the jar's shape, so honey is a liquid.

But now a spoon goes into the glass. It doesn't pour and stays spoon-shaped, so a spoon isn't a liquid.

Air fills the whole glass, but juice does not.

Here's the rule: a liquid pours and takes the shape of whatever holds it. It fills its container from the bottom up, with a flat top.

Okay, now your turn.

Here's a spoon in a tall glass. Cormac moves it to a wide bowl, then a square box.

What shape is it in the box? Still spoon-shaped.

The spoon keeps its own shape wherever you put it. A spoon is a kind of matter called a solid.

And now a wooden block. In the bowl or the box, it keeps its own shape.

And now a soft teddy bear. Squash it, put it down, and it's still bear-shaped: a solid.

But now Cormac pours milk into the box. It takes the box's shape, so milk is a liquid, not a solid.

So, three kinds. A gas fills all its space, a liquid takes its container's shape, a solid keeps its own shape.

Here's the rule: a solid keeps its own shape wherever you put it. Not a gas or a liquid means it is a solid.

Okay, now your turn.

Here's Tamsin pouring sand into a jar. It pours, just like juice.

So is sand a liquid? Let's look closely at one grain.

Each grain keeps its own shape. Each grain is a tiny solid.

Sand is many tiny solids: together they pour, but each keeps its shape.

And look at the top. Sand makes a heap, but a liquid's top goes flat.

And now a sponge. You can squash it, but it goes back to its own shape, so it's a solid.

And now fog. It's countless tiny drops of water floating in the air: a liquid, not a gas.

And now stuff shut in a box. You can't see what it does, so you can't tell yet.

To sort, ask what it does. Fills all its space: a gas.

Takes its container's shape: a liquid. Keeps its own shape: a solid.

Okay, now your turn.

The book and the air, the balloon at the gap, the long balloon, the juice, the spoon, the sand. Here's everything we found out.

Air is made of tiny pieces far too small to see.

And not just air. Every kind of matter is made of tiny pieces far too small to see.

You can see the book because its pieces are packed very close together.

Next, air takes up space. The air in the balloon took up the space, so the balloon was too big for the gap.

Air is a gas. A gas spreads out to fill all the space it is given.

Juice is a liquid. A liquid pours and takes the shape of whatever holds it, with a flat top.

A spoon is a solid. A solid keeps its own shape wherever you put it.

And the awkward ones. Sand is many tiny solids: each grain keeps its own shape.

A sponge is a solid. Fog is tiny drops of a liquid, floating in the air.

That's the whole topic: what stuff is made of, and how to sort any kind of stuff.

Okay, now your turn.

Here's an ice pop, left on a bench in the sun. Ten minutes later, it's a puddle and a stick.

Now let's look at the playground. A big puddle this morning. Gone by the afternoon. Where did all that water go?

And now let's take a cold can of soda outside. Soon it's wet all over. Where did that water come from?

Warming up and cooling down change water. This topic explains how the water changes, and why.

Okay, so are you ready to find out more?

Here's Juniper with an ice pop on a hot day. She puts it down on the bench.

What will she find when she comes back?

An ice pop is a solid: it keeps its shape. In the sun, it warms up.

When it warms up enough, it turns into a liquid.

That change is called melting. Juniper finds a puddle and a stick.

And now an ice cube on a warm plate. It warms up and melts.

And now butter in a hot pan. It warms up and melts.

And now a metal spoon in the same sun. It warms up, but it's not hot enough to melt.

Sugar stirred into cold water seems to go away. Nothing warmed it up: it mixed in, not melted.

Here's the rule: when a solid warms up enough, it turns into a liquid. That change is called melting.

Okay, now your turn.

Here's Tamar filling an ice-cube tray with water. She puts it in the freezer.

What will she find tomorrow morning?

Water is a liquid: it takes the tray's shape. The freezer's air is much colder.

The water gives some of its energy to the cold air and cools down. Nothing called cold goes in.

When it cools down enough, it turns into a solid: ice. That change is called freezing.

A thermometer shows when: thirty-two degrees Fahrenheit.

And now juice in a pop mold. It cools down enough and freezes.

And now melted butter in the fridge. It cools down enough and freezes.

A glass of water in the same fridge cools down, but not to thirty-two: still a liquid.

Here's the rule: when a liquid cools down enough, it turns into a solid, and that change is called freezing. Water freezes at thirty-two degrees Fahrenheit.

Okay, now your turn.

Here's a puddle on the playground after rain. In the morning it's big.

By lunchtime it's smaller. Next day the ground's dry.

Where did the water go?

Nobody mopped it up, and the ground isn't soaked. The puddle is open to the air.

Bit by bit, the water goes from the puddle's top into the air.

That change is called evaporation.

And now a wet T-shirt on the line. Its water goes into the air: it dries.

And now a saucer of water on a windowsill: less every day, until it's dry.

With a lid on, the water stays: the lid keeps it in.

Two puddles, one in sun, one in shade. The sunny one warms up and dries first.

Here's the rule: water open to the air goes into the air, bit by bit, and that change is called evaporation. Warm water evaporates faster.

Okay, now your turn.

Here's the playground where the puddle was. It's dry: the water went into the air.

Cosmo says the water is just gone, into nothing. Is he right?

Air is made of tiny pieces far too small to see. Water is too.

At the puddle's top, tiny pieces of water go off into the air, one by one.

They spread out through the air, like any gas, far too small to see.

Water in the air, as a gas you can't see, is called water vapor.

So Cosmo's not right. The puddle's water is still there, as water vapor in the air.

The shirt's and the saucer's water are in the air too.

On a muggy day you can feel it: the air feels damp and sticky.

Here's the rule: water that evaporates is still there, in the air. It is there as water vapor.

Okay, now your turn.

Here's a pan of water on the stove. Pippa's dad turns it on, then the phone rings.

An hour later, what will be in the pan?

The stove heats the water, and the thermometer climbs. At two hundred twelve degrees Fahrenheit, bubbles form all through it.

The water is boiling. Inside each bubble is water vapor.

The hot water turns into water vapor fast, and the water level gets lower.

After an hour the pan is dry. The water is all in the kitchen air, as water vapor.

Here's the rule: at two hundred twelve degrees Fahrenheit, water boils. Bubbles form all through it, and the water turns into water vapor fast.

Okay, now your turn.

Here's a pan of water bubbling on the stove, and a puddle on a warm path.

Both are losing water into the air.

Are they doing the same thing?

No: you can see the difference.

First the puddle: it has no bubbles, and its water goes into the air from the top only.

It's slow, and it happens at any warmth.

That is evaporating.

Now the pan: it has bubbles of water vapor all through its water, not just at the top.

It's fast, and it happens only at two hundred twelve degrees Fahrenheit.

That is boiling.

With the stove turned down, the bubbles stop: the water is still hot, but now it's evaporating, not boiling.

Here's the rule: evaporating is slow, from the top, with no bubbles, at any warmth; boiling is fast, with bubbles all through, only at two hundred twelve degrees Fahrenheit.

Okay, now your turn.

Here's Florrie with a cold can of orange soda, outside on a warm day.

Soon the can's outside is wet.

Where did the water come from? Did the soda come through the can?

No, it didn't: the drops are clear, not orange, and the can is sealed. So the water came from outside.

The air has water vapor in it. It touches the cold can and cools down.

When it cools down enough, it turns back into liquid water. Drops form on the can.

That change is called condensation.

And now a cold window on a winter morning. The room's water vapor condenses on it: mist.

And now a can at room warmth beside it: not cold, so no drops form.

Here's the rule: when water vapor touches something cold, it turns back into liquid water, and drops form. That change is called condensation.

Okay, now your turn.

Here's Zosia with an ice cube in a cup. It melts into a clear liquid.

Bertie says that's not water, that's melted ice, a different stuff. Is he right?

No, he's not right. That's because Zosia froze water in a tray to make the cube, so the ice was water, frozen.

The liquid in the cup is water: the same water.

Freeze it, and it's ice again. Let it evaporate, and it's water vapor: still water.

Let it condense on a cold window, and it's drops of water again.

Ice, water and water vapor are the same stuff: water.

Solid, liquid or gas: which one a thing is, we call its state.

A sealed bag of ice reads two hundred grams. Melted, still two hundred.

Here's the rule: melting, freezing, evaporating, boiling and condensing change water's state. The stuff stays the same: it is still water.

Okay, now your turn.

The ice pop, the ice-cube tray, the puddle, the pan, the cold can. Here's everything we found out.

First, melting. When a solid warms up enough, it turns into a liquid: it melts.

Then freezing. When a liquid cools down enough, it turns into a solid: it freezes. Water freezes at thirty-two degrees Fahrenheit.

Next, the puddle. Water left open to the air goes into the air, bit by bit: it evaporates.

And that water is not gone. The water that evaporated is still there, in the air, as water vapor.

When water heats up to 212 degrees Fahrenheit, it boils, and it turns into water vapor fast. Boil it long enough and the pan boils dry.

Then back again. When water vapor touches something cold, it turns back into liquid water: it condenses.

And through all of it, one thing never changes. Ice, water and water vapor are the same stuff: water.

Heating and cooling change the state, never the stuff.

Okay, now your turn.

Here's a town on a summer evening. The sky has gone dark, and the wind is picking up.

So is a storm coming? Nobody can see tomorrow's weather: the river might flood tonight, or tomorrow might be another hot, dry day.

But people who watch the weather can say what is likely, because they measure today's weather and write it down, day after day, until the pattern shows.

They measure how warm the air is, where the wind is from, and how much rain fell, and a table holds every answer.

To find out, we will look at measuring today's weather, writing it down, and reading it back.

Okay, so are you ready to measure the weather?

Here's Caleb at the window on Tuesday morning, one arm out. Chilly, he says.

Rowena says it isn't chilly. So how warm is the air, really?

Here's the thermometer outside the door, in the shade.

Two marks above sixty: sixty-two, sixty-four degrees Fahrenheit. How warm a thing is, as a number, is called its temperature.

It's in the air outside, so it measures how warm the air outside is.

The classroom thermometer is in the air inside, so it measures that air: seventy degrees.

And now a thermometer in Caleb's mug of milk. It's in the milk, so it measures the milk, not the air: ninety-eight degrees.

So, a thermometer measures how warm the thing it is in is. Hang it outside, in the shade, and it measures how warm the air is.

Sixty-four degrees: the air's temperature. Caleb and Rowena have their number.

Okay, now your turn.

Here's Odin on the playground. The wind blows his hair straight back.

Where's this wind from? Nobody can see wind, but the vane on the roof can show him.

Here's the vane from above: N for north, E for east, S for south, W for west, and an arrow with a sharp point and a wide tail.

Now the wind blows from the north. The arrow's point swings round to the N.

The arrow points into the wind. The letter under the point says where it's from: a north wind.

And now the wind blows from the west. The point swings to the W: a west wind.

Why? The wind pushes the wide tail away, so the point turns to face the wind.

So, here's what we've seen. The arrow points into the wind. The letter under the point says where the wind is from.

Okay, now your turn.

It rained in the night, but by morning the puddles have dried up.

Gemma says a lot fell. Rudy says only a little. How much?

Here's the rain gauge in the school garden: a marked tube standing in the open.

Yesterday evening the class emptied it. Zero millimeters.

This morning there's water in it. First, find where the water's top lies.

Next, the number just below the top: zero. Count up in twos: two, four, six.

Six millimeters of rain fell in the night.

Look closer: the water curves at the glass. Read from the bottom of the curve.

A wet Wednesday: two marks above ten. Twelve, fourteen millimeters.

Some gauges have marks worth one, five or ten millimeters: count the spaces.

So, a rain gauge measures how much rain fell. Find the water's top, read the number below, count up mark by mark.

Okay, now your turn.

Here's Ivar's desk after a week of weather watching: every reading on its own scrap.

Which day had six millimeters of rain? Nobody can tell.

Here's a table with five headings: Day, Temperature, Wind from, How windy, Rain. Each says what goes below it.

Under a heading, boxes go down in a column. Across, they go along in a row, one row for each day.

Monday: seventy-two degrees from the thermometer, W for west from the vane, breezy, zero millimeters from the gauge, all in Monday's row.

Tuesday gets the next row: sixty-four degrees, N for north, windy, six millimeters.

Now, which day had six millimeters of rain? The six sits in Tuesday's row.

Now let's take the headings away. Nobody knows what the six is.

So, one row for each day, one column for each thing you record, and a heading that names each column.

Okay, now your turn.

Here's Fitz copying the class weather table into his notebook. Seventy-two degrees Fahrenheit. Sixty-four degrees Fahrenheit. Fifty-eight degrees Fahrenheit.

The same two words in every box, and his hand is aching. Is there a shorter way?

Here's the class table. The unit sits in the top row, beside the heading: Temperature, degrees Fahrenheit. Rain, millimeters.

It's written once. Every number in that column is in that unit.

So Wednesday's fifty-eight means fifty-eight degrees Fahrenheit, and Wednesday's fourteen means fourteen millimeters.

Now let's take the units away. Is the six six millimeters? Six degrees? Nobody can tell.

So, the unit goes in the top row, beside the heading, written once. Every number in that column is in that unit.

Fitz writes it once, and his hand can rest.

Okay, now your turn.

It's Thursday morning. Three rows of the table are filled; Thursday's row is empty.

Outside stand the three instruments. Which reading goes where?

Each column has its own instrument. Temperature: the thermometer. Wind from: the wind vane. Rain: the rain gauge.

First, the thermometer. Three marks above sixty: sixty-two, sixty-four, sixty-six. Sixty-six degrees goes under Temperature.

Next, the wind vane. The point sits on the E: the wind is from the east. E goes under Wind from.

Last, the rain gauge. One mark above zero: two millimeters. Two millimeters goes under Rain.

The class writes how the wind felt: calm. Thursday's row: sixty-six, E, calm, two.

Rowena looks at the gray sky and says, write ten under Rain. But the sky didn't measure the rain; the gauge did.

So, for each column, read the instrument that measures that thing, and write the reading in today's row.

Okay, now your turn.

It's Friday. Talia says Tuesday was colder than Wednesday. Rudy says no, Wednesday was colder.

Nobody remembers. But the class weather table does.

Let's find Wednesday's temperature. First, find the day's row: look down the Day column for Wed.

Next, find the column with the right heading: Temperature.

Go along Wednesday's row to the Temperature column.

The box where they meet holds the value: fifty-eight degrees Fahrenheit.

Now Tuesday's rain. Tuesday's row, the Rain column. Where they meet: six. Six millimeters.

Now let's go back to Talia and Rudy. Tuesday's temperature: sixty-four degrees. Wednesday's: fifty-eight degrees.

Sixty-four is bigger, so Tuesday was warmer and Wednesday was colder. Rudy was right.

So, find the day's row. Find the column with the right heading. The box where they meet holds the value.

Okay, now your turn.

Here's everything we found out about measuring the weather.

First, the thermometer. A thermometer measures how warm the thing it is in is, so hung in the shade it measures how warm the air is.

Next, the wind vane. The wind vane's arrow points into the wind.

The letter under the vane's point says where the wind is from.

Then the rain gauge. A rain gauge measures how much rain fell, in millimeters. Find the water's top, read the number below.

Count up mark by mark.

Now the table. One row for each day, one column for each thing you record, a heading on every column.

The unit goes in the top row, written once.

To fill today's row, read each instrument and write its reading in today's row.

To read it back, find the day's row and the right column: the box where they meet holds the value.

Wednesday, fifty-eight degrees. Tuesday, sixty-four degrees. Wednesday was colder: Rudy was right.

Measure it, write it down, read it back.

Okay, now your turn.

Here's Yasmin in Columbus, Ohio, on a video call with her cousin Elio in Phoenix, Arizona.

Behind Yasmin, snow is falling. But behind Elio, the sun is blazing, on the very same day.

Then Elio asks about July, when Yasmin comes to visit. Should she pack a raincoat, or a sun hat?

But next July hasn't happened yet. Nobody has seen its weather.

To find out, we will look at what a season's weather is usually like, here and far away, and how the class weather table can tell you.

Okay, so are you ready to find out what the weather is usually like?

Here's a bar graph Yasmin's class made. One bar for each school day in May.

Elio asks, "How warm was it on Wednesday?"

The words along the bottom name the days. The numbers up the side give the temperature.

Monday first. Find the top of the bar, and follow it across.

It lands on seventy, so Monday was seventy degrees.

Now Wednesday. The top lands between seventy and eighty.

Two spaces between seventy and eighty, so each line is worth five degrees. That line is seventy-five.

So Wednesday was seventy-five degrees.

And Thursday: the top lands right on eighty, so Thursday was eighty degrees.

Now the fall graph: October lands on seven rainy days, September on four, so October had three more rainy days.

So, to read a bar graph: find the top of the bar, follow it across, and read the number it lands on.

Okay, now your turn.

All spring, Yasmin's class kept the weather table, then counted each month's rainy days.

Six rainy days in March, eight rainy days in April, three rainy days in May.

Her teacher asks, "Can you show the whole spring in one picture?"

Let's make a bar graph. First the labels: Rainy days and the numbers up the side, the months along the bottom.

Now one bar for each month. March had six rainy days, so March's bar goes up to the six.

April had eight rainy days, so its bar goes up to the eight.

May had three rainy days, so its bar goes up to the three, the line between two and four.

Now the whole spring is one picture. April's bar is tallest, so April had the most rainy days.

So, write the labels, then draw one bar for each month, up to its number.

Okay, now your turn.

Yasmin is visiting her cousin Elio in Phoenix next July. Raincoat, or sun hat?

Next July hasn't happened yet. So how can anyone say what it'll be like?

Elio's class kept a weather table for three years. Here are the rainy days in each July.

Two rainy days, three rainy days, one rainy day. Every July had only a few.

And the hot days: twenty-eight hot days, thirty hot days, twenty-six hot days. Every July had many.

The same thing happened three years in a row. That's a pattern, and a pattern lets you say what happens next.

So next July is likely to be the same: hot, with three or fewer rainy days.

The weather a season usually has, year after year, is called its typical weather.

Here's the pattern: if the same weather came every year, it's likely to come again next year.

Okay, now your turn.

Here's everything we found out about a season's weather.

First, reading a bar graph. To read a bar, find its top, follow it across, read the number it lands on.

If it lands between two numbers, work out what each line is worth.

Next, making one. A bar graph shows a whole season at a glance.

Draw one bar for each month, up to its number: March six rainy days, April eight, May three.

Then Elio's three Julys: one to three rainy days and twenty-six or more hot days, every year.

The weather a season usually has, year after year, has a name.

It is called its typical weather.

The same weather every year is likely to come again next year. So Yasmin packed the sun hat.

Then the video call. Two places can have different weather on the same day: read the same column for both.

Last, the map. Far away, the typical weather can be very different from here.

That's a season's weather in one picture, here and far away.

Okay, now your turn.

Here's a road in Hawaii. Yesterday, cars drove along it. Today it's gone, under a layer of dark rock.

Here's a street in California. Last night it was whole. This morning a crack runs right across it.

And here's a hill above a valley road. Yesterday, trees covered it. Today the trees lie in a heap on the road.

Hills, roads, fields: most days they look the same as the day before. So what can change the land in one day?

To find out, we will look at what changes the land fast, and what each one does to it.

Okay, so are you ready to find out what changes the land fast?

Here's Mount Saint Helens. And here's Pikes Peak. One of them is a volcano.

Deep inside Earth, some rock is so hot that it has melted.

In some places there's an opening in the ground. The melted rock comes up through it, and out.

The melted rock that comes out is called lava.

Now Pikes Peak. No opening, no melted rock. Not a volcano.

And now Kilauea, in Hawaii. Melted rock comes out of the opening at its top. So it is a volcano.

Now let's go back to Mount Saint Helens. Nothing comes out today, but melted rock has come out before. A volcano.

And now Old Faithful. Hot water shoots out of an opening, but hot water isn't melted rock. Not a volcano.

So, a volcano is an opening in the ground where melted rock from deep inside Earth comes out.

Okay, now your turn.

Here's the land below a volcano: a green field, three trees, and a road.

Now melted rock comes out of the opening: the volcano erupts. Lava pours out.

Lava is a liquid, so it flows downhill: over the grass, over the trees, over the road.

It's so hot that the grass and the trees burn.

Out in the air, the lava cools. It turns into solid rock: dark gray, hard rock.

The field is gone. The road is gone. New rock lies where they were.

How long did that take? One day.

Now suppose lava flows over a parking lot. It cools. New solid rock lies on top of the parking lot.

So, when a volcano erupts, lava pours out and covers the land. The lava cools and turns into solid rock.

Okay, now your turn.

Here's Hazel at breakfast in California. Suddenly the floor shakes and the pictures rattle.

Twenty seconds later, everything is still. What just happened?

The floor didn't shake on its own. The ground under the house shook, and the house with it.

A sudden shaking of the ground is called an earthquake. It lasts about twenty seconds in a big one, then it stops.

Now a truck rumbles past a house. The window rattles, but the ground stays still. Not an earthquake.

And now Miles, on a park bench. The ground under his feet shakes, suddenly. An earthquake.

And now a windy day. The trees shake, but the ground stays still. Not an earthquake.

Earthquakes happen in California, Alaska, Oklahoma, and many other states.

So, an earthquake is a sudden shaking of the ground. It lasts about twenty seconds in a big one, then stops.

Okay, now your turn.

Here's Camila's street, in California. Last night an earthquake shook it for about twenty seconds.

This morning, a crack runs right across the road. One side is a step higher.

Let's watch a road. Before the earthquake, it's straight and whole.

The earthquake strikes. The ground shakes hard, and it cracks in places.

One crack runs across the road, about as wide as your hand. One side ends up a step higher.

Twenty seconds later, the shaking stops. The crack and the step stay.

The ground doesn't open up and swallow houses. The cracks are narrow.

Now suppose an earthquake shakes a flat field. Cracks can run across it, and one side can sit a step higher.

So, when an earthquake strikes, the ground can crack, and one side can end up a step higher than the other. It takes seconds.

Okay, now your turn.

Here's Elliot and his dad below a steep hillside in California. It's rained for three days.

A rumble. Then the whole hillside slides down onto the path, trees and all.

Ground that goes downhill is a slope. Most days, its soil and rock stay where they are.

Here's a flat field in the rain. No slope, so nothing slides. Not a landslide.

And now Elliot's hillside after three days of rain: the soil is soaked, and suddenly a mass of soil, rock and trees slides down. A landslide.

And now a dry, rocky slope in Alaska. The ground shakes, and rock slides down. A landslide, too.

And now the same hillside, another day. A little mud washes down; the hill stays. Not a landslide.

So, a landslide is a mass of rock or soil suddenly sliding down a slope. Heavy rain can start one.

Okay, now your turn.

Here's Javier and his mom on the valley road. A heap of soil, rocks and trees lies across it. Where did it come from?

Let's look at a hillside before a landslide: trees on the slope, a road along the valley floor.

It rains for days. Suddenly a mass of soil and rock slides down the slope, trees and all.

In less than a minute, it stops.

Where the soil was, the slope is bare ground now: no grass, no trees.

Where the soil went, a heap lies on the valley floor. The road is under it.

Now suppose a mass of soil slides onto a stream. The heap lies across the stream, and the water spreads out into a pond.

So, when a landslide happens, the slope is left as bare ground, and a heap of soil and rock lies at the bottom.

Okay, now your turn.

Here's what we found out about volcanoes, earthquakes and landslides.

First, the volcano. A volcano is an opening in the ground where melted rock from deep inside Earth comes out.

The melted rock is called lava: rock so hot that it glows.

Lava covers the land and cools into solid rock. The field is gone in one day.

Next, the earthquake. An earthquake is a sudden shaking of the ground, about twenty seconds in a big one.

The ground can crack, and one side can end up a step higher than the other. The crack stays.

Then, the landslide. A landslide is a mass of rock or soil suddenly sliding down a slope. Heavy rain or shaking ground can start one.

The slope is left as bare ground, with a heap of soil and rock at the bottom, in less than a minute.

New rock on a field: a volcano erupted. A crack across a road: an earthquake. Bare ground above and a heap below: a landslide.

Okay, now your turn.

Here's a town beside a river. After three days of rain the river is rising, and water is spreading across the road toward the houses.

Nobody can stop the rain. But the people aren't just watching: they're stacking sandbags along the bank as fast as they can.

The water is already lapping at the bags.

Then, in the morning, a fence lies flat in the mud. So what knocked it down: the water, or the wind that blew all night?

To find out, we will look at what dangerous weather can do, how people hold it back, and how to work out what really happened.

Okay, so are you ready to find out what dangerous weather can do?

Here's Isadora at her window. Three days of rain, and the river's high.

Can rain really do any damage?

The river rises over its banks, and water spreads to the doors: a flood.

Flood water soaks the ground floor.

Now let's go to the Florida coast. A hurricane is a huge storm from the sea, and it brings strong wind.

Strong wind tears shingles off roofs and knocks trees down.

Now let's visit a farm in a thunderstorm. Lightning can set a roof on fire, so when it thunders, go indoors.

And now a blizzard in Minnesota brings deep snow that blocks the roads.

So, here's what we've seen. Dangerous weather causes damage: it brings flood water, strong wind, lightning or deep snow. Each kind of dangerous weather does its own damage.

Okay, now your turn.

Here's Rupert at his front door. The river is rising again.

Last spring, flood water came in under this door. Nobody can stop the rain, so what can he do?

He and his dad stack sandbags across the doorway, and the sandbags hold the water back.

Inside, the floor stays dry. Something built so that weather does less damage is called a defense.

Now let's look at the whole town. A long bank along the river, a levee, holds back flood water.

Storm shutters hold back strong wind. A lightning rod gives lightning a safe path to the ground.

And a snow fence catches blowing snow before it reaches the road.

But a levee can't hold back wind. A defense works when it holds back what is coming.

Here's the pattern. Nobody can stop the weather, but a defense can hold back what it brings.

Okay, now your turn.

Here's Harriet in her yard on Tuesday morning. The fence is flat on the grass.

Why did it fall? Her brother says a cow. Her mom says the wind. Her dad says it was old and fell by itself.

An idea about why something happened is called an explanation. Which explanation is best?

Here's what Harriet observed: branches all over the yard, wind howling all night, no cows near, and new posts with no rot.

No cows live near the yard, so the cow explanation doesn't fit.

New posts, so an old fence doesn't fit. Wind all night, branches down: the wind fits everything.

Her brother likes the cow explanation. But liking it doesn't make it fit.

So, the best explanation is the one that fits everything you observed. Check each one against every observation, and choose the one that fits them all.

Okay, now your turn.

Here's what we found out about dangerous weather.

First, the weather. Dangerous weather causes damage: it brings flood water, strong wind, lightning or deep snow.

Flood water soaks the ground floor, wind knocks trees down, lightning can set a roof on fire, snow blocks the roads.

Most weather does no damage: one rainy afternoon fills two puddles.

Next, defenses. Nobody can stop the weather, but a defense can hold back what it brings.

Sandbags and a levee hold back flood water. Storm shutters hold back strong wind.

A lightning rod gives lightning a safe path to the ground. A snow fence keeps deep snow off the road.

A levee can't hold back wind.

Then, explanations. An idea about why something happened is an explanation. Harriet's fence fell: maybe a cow, maybe the wind.

The best explanation is the one that fits everything you observed. Branches down, the wind howling all night, no cows near: the wind fits everything.

Not the one you like. The one that fits.

Okay, now your turn.

Here's a forest floor in the fall. Leaves drift down, as they have every fall for hundreds of years.

So by now it should be buried in leaves. But it isn't: a thin layer, and under it, the ground.

Look closely at that ground. Pale, hard bits. Dark, soft crumbs. A piece of an old leaf.

So where did all those leaves go, and where did the pale bits come from?

And the ground here is loose and gritty, while the ground by the stream is sticky.

To find out, we will look at what soil is made of, where it came from, and how to tell one soil from another.

Okay, so are you ready to dig into soil?

Here's Meera in the school garden with a scoop of soil. Just dirt, says Lyle. Dirt is dirt.

Let's look closer, through a round glass that makes small things look bigger: a magnifying glass.

Some bits are pale and hard. Meera presses one with a pin: it doesn't squash. Those are bits of rock.

Some bits are dark and soft. Here's a bit of a leaf. Here's a bit of twig. Those are bits of dead plants.

Now let's take the soil apart another way. Meera puts a spoon of soil in a jar of water and shakes it.

An hour later, the bits of rock have sunk to the floor.

Most of the bits of dead leaves float at the top.

So, here's what we've seen. Soil is made of broken bits of rock mixed with bits of dead plants and animals.

Okay, now your turn.

Here's Kezia at the beach. Sand everywhere, and every grain is a tiny bit of rock. Where did they all come from?

Here's a big rock on the cliff. A crack runs down it. At the bottom of it lie pieces that have broken off: big pieces, pebbles, and grit, tiny bits of rock.

Now consider one pebble. The waves roll it against other pebbles, year after year. Tiny bits rub off. The pebble gets smaller and rounder.

The bits that rub off are grains of sand. So a grain of sand was once part of a bigger rock.

Boulder, rock, pebble, grit, grain of sand. All the same stuff, smaller and smaller. And it takes far longer than a person lives.

So, the bits of rock in soil come from bigger rocks slowly breaking apart.

Okay, now your turn.

Here's Roshan in the fall, raking the dead leaves under the oak into a big pile.

Now it's spring. The pile is small. Under the top leaves, it's dark and crumbly. Where did all the leaves go?

Let's look under a hedge, where leaves fall every year. Here's a cut through the ground.

At the top, whole leaves, from this fall. Lower down, leaves in bits. At the bottom, dark crumbs. You can't tell they were leaves.

A dead leaf slowly goes soft, falls apart, and turns into dark crumbs. We say it rots. And the crumbs mix into the soil.

An apple core rots. A dead beetle rots. A pebble doesn't: it's rock, not a dead thing.

So, here's what we've seen. The dark crumbs in soil come from dead plants and animals rotting away. The leaves didn't vanish. They became part of the soil.

Okay, now your turn.

Here's Flora filling two pots. Soil is soil, she says. Brown is brown. Is it?

Here are three soils on three plates. Look: pale yellow-brown, orange-brown, dark brown. Not the same brown at all.

Flora feels them. Gritty, like sand. Smooth and sticky. Soft and crumbly.

Now let's test them. One full cup of water on each soil, in a cup with holes, over a jar. One minute later:

Through the pale soil, the water runs fast. On the orange soil, it sits. Through the dark soil, some runs through.

Pale, gritty, fast: sandy soil. Orange, sticky, sits: clay soil. Dark, crumbly, some: garden soil.

To tell two soils apart, look at their color, feel them, and test how fast water runs through.

Okay, now your turn.

A scoop of soil. Here's everything we found out about it.

First, what soil is. Soil is made of broken bits of rock mixed with bits of dead plants and animals.

Shaken in a jar of water, the bits of rock sink and most of the dead leaves float.

Next, the bits of rock. The bits of rock in soil come from bigger rocks slowly breaking apart.

Boulder, rock, pebble, grit, grain of sand: all the same stuff, smaller and smaller.

Then, the dark crumbs. The dark crumbs in soil come from dead plants and animals rotting away.

Whole leaves at the top, leaves in bits below, dark crumbs at the bottom: the leaves became part of the soil.

And last, telling soils apart. To tell two soils apart, look at their color, feel them, and test how fast water runs through.

Pale, gritty, fast: sandy soil. Orange, sticky, sits: clay soil. Dark, crumbly, some: garden soil.

Bits of rock and bits of dead things, mixed.

Okay, now your turn.

Here's Lumi by a river with her class. She turns over a flat gray rock, and there on it is the shape of a fish, bones and all.

But there's no fish. There's nothing you could pick up, just its shape, pressed into solid rock.

Most dead things rot away and are gone. Yet this one has lasted, in solid rock, for a very long time.

So how did it last, and what can it tell us about the fish, and about this place, long ago?

To find out, we will look at the few dead things that last, and what they tell us about long ago.

Okay, so are you ready to find out what fossils can tell us?

Here's Hal's pumpkin on the ground by the porch step, the day after Halloween.

By December it's soft and caved in. By spring, only a dark patch is left. Where did it go?

It rotted away, and became part of the soil.

A dead fish on a riverbank rots in weeks; its bones crumble in years.

Now let's go back a very, very long time. A dinosaur leaves a footprint in mud.

The sun dries the mud. New mud covers the print, piles up, and hardens into rock.

The dinosaur rotted away. Its footprint lasted.

A shell buried in mud lasts millions of years. In the open, it crumbles.

So, after a living thing dies, its body usually rots away and becomes part of the soil. Sometimes a hard part or a print gets buried fast, and it lasts a very, very long time.

Okay, now your turn.

Here's Romy at a riverbed. She picks up a flat rock with a curly shell shape pressed in it.

There's no shell, only its shape. What made it, and how long ago?

Here's a dinosaur's footprint in rock. Long ago it pressed its foot into mud. The mud hardened, and the print lasted.

It's a mark a living thing made. So is a leaf print.

Now here's a bone in rock. The soft body rotted away; the bone got buried and lasted. It's a part of a living thing.

A part of a living thing from long ago, or a mark it made, that has lasted until today, is called a fossil.

A footprint is a fossil. A leaf print is a fossil. Not only dinosaur bones.

Romy's shell shape is a mark a sea animal left, long ago. She has found a fossil.

Okay, now your turn.