Topic 9 Balanced forces — what needs James (0)

Topic 9 · Balanced forces · Type 1 · bank item PP-1 · tests FOR3-040

EasyMCQType 1 — two named children each pull one end of a rope: which is true of the two pulls

Amal and Zayn each pull one end of the same rope, toward themselves. Which is true about the two pulls?

1. a) Both pulls act on the rope at the same time. ← key
2. b) Only Amal's pull acts on the rope.
3. c) Only Zayn's pull acts on the rope.
4. d) Neither pull acts on the rope.

Why it is this type: Amal pulls the rope. / Zayn pulls the rope. / More than one force can act on the same object at the same time. / So both pulls act on the rope at the same time.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 2 · bank item PP-2 · tests FOR3-041

EasyMCQType 2 — a still object: which forces act on it (the Force Concept Inventory's book-on-table item, grade 3 wording)

A plant pot stands still on a windowsill. Which forces act on the pot?

1. a) only Earth's pull
2. b) only the windowsill's push
3. c) no forces at all
4. d) Earth's pull and the windowsill's push ← key

Why it is this type: A still object can have pushes and pulls acting on it. / Earth pulls the pot down. / The windowsill pushes the pot up. / So two forces act on the pot at the same time.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 3 · bank item PP-3 · tests FOR3-042

EasyMCQType 3 — four drawings J K L M of two opposite arrows on one towel: in which are the forces balanced

Two children each pull one end of a towel. In which drawing are the forces on the towel balanced?

1. a) drawing J
2. b) drawing K ← key
3. c) drawing L
4. d) drawing M

Figure: four panels J K L M of the same two children each pulling one end of a striped towel; both blue arrows start at the towel's middle. J: the left arrow longer. K: the two arrows the same length. L: the right arrow longer. M: the right arrow longer, both arrows short.

Why it is this type: Two opposite forces are balanced when they are the same strength, and a longer arrow shows a stronger force. / In J, L and M one arrow is longer than the other. / In K the two arrows are the same length. / So drawing K shows balanced forces.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 4 · bank item PP-4 · tests FOR3-043

EasyMCQType 4 — a still object with balanced forces: what does it do

A jar stands still on a kitchen counter, and the forces on the jar are balanced. What does the jar do?

1. a) It starts to slide.
2. b) It stays still. ← key
3. c) It falls off the counter.
4. d) It rises up.

Why it is this type: The jar is still. / The forces on it are balanced. / While the forces on a still object are balanced, it stays still. / So the jar stays still.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 5 · bank item PP-5 · tests FOR3-045

EasyMCQType 5 — a moving object with balanced forces: what does it do

A tram moves along a straight street, and the forces on it are balanced. What does the tram do while the forces stay balanced?

1. a) It speeds up.
2. b) It slows down.
3. c) It turns.
4. d) It keeps the same speed. ← key

Why it is this type: The tram is moving. / The forces on it are balanced. / While the forces on a moving object are balanced, it keeps the same speed and the same direction.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 6 · bank item PP-6 · tests FOR3-042

EasyMCQType 6 — the forces on a bag are balanced: what do you know about the two pulls

Two children each pull one strap of a bag in opposite directions, and the forces on the bag are balanced. What do you know about the two pulls?

1. a) The left pull is stronger.
2. b) The right pull is stronger.
3. c) They are the same strength. ← key
4. d) Only one of them is really acting.

Why it is this type: Two opposite forces are balanced when they are the same strength. / The forces on the bag are balanced. / So the two pulls are the same strength.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 10 · bank item PP-7 · tests FOR3-040

ProposedEasyProposed: Type 10 — which is true about the forces on one object (the golden set's Q5.1 / Q5.2 / M16 probe as four options)

Which is true about the forces on one object?

1. a) Only one force can act on it at a time.
2. b) Two forces can act on it, but never more than two.
3. c) More than one force can act on it at the same time. ← key
4. d) No force acts on it while it is still.

Why: More than one force can act on the same object at the same time. / A wagon on grass has four: a pull, a drag, Earth's pull and the ground's push. / A still book has two. / So more than one force can act on one object.

Why it is this type: James — "You're also not reusing some of the questions from my golden forces set, which were designed specifically to test misconceptions like 'How many forces can an object act on at once?' … You need those types of questions throughout, but also particularly in the PP100s." The golden set asks it as true / false (Q5.1, Q5.2, M8, M16); the bank asks it with four options, each distractor a belief the catalogue lists.

Recommendation: Approve the proposed type

Topic 9 · Balanced forces · Type 7 · bank item PP-8 · tests FOR3-045

MediumMCQType 7 — Mabli says balanced means standing still: which object shows she is mistaken

Mabli says that when the forces on an object are balanced, the object must be standing still. Which object shows that Mabli is mistaken?

1. a) a car parked in a driveway
2. b) a book lying on a table
3. c) a sled gliding at a steady speed ← key
4. d) a vase standing on a shelf

Why it is this type: Balanced forces leave the motion as it is. / The parked car, the book and the vase are still, so they fit what Mabli says. / The sled is moving, and its forces are balanced because its speed and direction are not changing. / So the gliding sled shows Mabli is mistaken.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 8 · bank item PP-9 · tests FOR3-042

MediumtypedType 8 — two opposite forces of the same strength: type the word

TEXT ENTRY

Two opposite forces act on one object, and they are the same strength. Type the word we use for these forces.

Accepted answers (typed): balanced · balanced forces

Why it is this type: Two opposite forces are balanced when they are the same strength.

Recommendation: Approve as the exemplar

Topic 9 · Balanced forces · Type 11 · bank item PP-10 · tests FOR3-045

ProposedMediumProposed: Type 11 — a ball rolls at a steady speed in a straight line: which is true of the forces (the Force Concept Inventory's steady-motion item, adapted)

A ball rolls across a flat floor in a straight line at a steady speed. Which is true about the forces on the ball?

1. a) The forces on the ball are balanced. ← key
2. b) The push forward is stronger than the drag back.
3. c) The drag back is stronger than the push forward.
4. d) No forces act on the ball.

Why: The ball's speed is not changing. / Its direction is not changing. / A moving object keeps the same speed and direction while the forces on it are balanced. / So the forces on the ball are balanced.

Why it is this type: James — "there are probably some great MCQs that you could probably use from the physics force concept inventory. You can sort of reuse similar diagrams and similar questions." The FCI's puck sliding at a constant speed asks which forces act; the grade 3 version asks whether the forces are balanced, with the FCI's two misconceptions (a push must be winning; nothing acts) as distractors. Medium because: the student infers the forces from the stated motion, not the motion from stated forces.

Recommendation: Approve the proposed type

Topic 9 · Balanced forces · Type 12 · bank item PP-11 · tests FOR3-045

ProposedMediumProposed: Type 12 — which of four movers has balanced forces on it (balanced ≠ still; three changes of motion — the seam to Topic 10)

Which of these has balanced forces on it?

1. a) a sled speeding up down a hill
2. b) a bike slowing down
3. c) a car turning a corner
4. d) a train moving at a steady speed along a straight track ← key

Why: Balanced forces leave the motion as it is. / Speeding up, slowing down and turning are changes of motion. / The train's speed and direction are not changing. / So the train has balanced forces on it.

Why it is this type: James — "We need to correlate [balanced or not balanced] with speeding up, slowing down, or changing direction." The golden M19 asks it as true / false; here the student picks the one mover whose motion is not changing from three that are. Medium because: three of the four are changes of motion the student must recognise as changes.

Recommendation: Approve the proposed type

Topic 9 · Balanced forces · Type 9 · bank item PP-12 · tests FOR3-045

HardMCQType 9 — a drawn suitcase moving right, her pull and the floor's drag from its centre, equal: while the arrows stay like this, what does it do

MCQ

The drawing shows a girl's pull and the floor's drag on a suitcase moving to the right. While the arrows stay like this, what does the suitcase do?

1. a) It keeps the same speed. ← key
2. b) It speeds up.
3. c) It slows down.
4. d) It stops.

Figure: the girl pulls the suitcase to the right; a grey dashed MOVING cue points right above it; from the suitcase's centre a blue arrow points forward, labelled her pull, and a blue arrow points back, labelled the floor's drag; both on one line, the same length. No chip says balanced, steady or same. (The 28 Sep drawing had the pull tilted along the handle and the drag lower and horizontal — James: "the arrows are in different angles".)

Why it is this type: Hard because: two steps — read the two arrows as the same length, so the same strength, so balanced; then predict what a moving object does while its forces are balanced. (Was a typed one-word cloze; James: "a pointless FRQ. There are much better MCQs we can use here." Hard items need not be typed, his ruling of the same day.)

The why line (what a student reads after answering): The two arrows are the same length, so the pull and the drag are the same strength. / Two opposite forces of the same strength are balanced. / While the forces on a moving object are balanced, it keeps the same speed and the same direction. / So the suitcase keeps the same speed.

Recommendation: Approve as the exemplar