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Introduction to Forces

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Introduction to Forces

A community science team is testing a small cart for a local seaside track. Use the story and diagrams to investigate how forces affect motion. A force is a push or pull; it can change an object's speed, direction or shape. Answer in complete sentences where asked.

A. Forces in action

Read the scenario: Maia gives the cart a shove. It rolls along the path, slows down, and stops. Later, she pulls it back using the rope. When it reaches a sloping section, it rolls downhill.

1.Which statement best describes a force?

A push or pull that can change motion or shape
A substance that makes objects heavier
A kind of sound made by moving objects
A measure of how far an object travels

2.Maia first shoves the cart, then pulls it back with the rope. Identify the force in each action and explain what makes each one a push or a pull.

3.Select all the changes a force can cause.

Start an object moving
Stop a moving object
Change an object's direction
Change an object's speed
Change an object's colour by itself
Squash or stretch an object

B. What changes the cart's motion?

Use this force sketch. The arrows show forces acting on a cart; longer arrows mean stronger forces.

Sketch 1: ← 3 N [CART] 3 N → (level track; cart initially still)

Sketch 2: [CART] 5 N → (level track; no other horizontal force shown)

Sketch 3: [CART] 4 N → 2 N ← (level track)

4.In Sketch 1, the forces are equal and opposite. What is the overall (resultant) horizontal force, and what would happen to the cart if it starts still?

5.In Sketch 2, find the resultant horizontal force and predict how the cart's motion will change.

6.In Sketch 3, find the resultant horizontal force. Which way will the cart accelerate?

7.The cart rolls on a flat path and gradually slows after Maia stops pushing. What force from the path and air helps slow it down? Explain how it affects motion.

C. Test, explain, improve

Think like a careful investigator: distinguish what you observe from what you infer, and connect each claim to a force.

8.The cart travels downhill without anyone pushing it. Which force pulls it towards the ground and helps it move downhill?

9.A student says, “If no one is pushing a cart, it must stop immediately.” Is this always correct? Use the idea of forces to explain.

10.Maia wants the cart to travel farther after one shove. Suggest one fair test change that could reduce an opposing force, and state what she should keep the same to make the comparison fair.

11.Draw a force-arrow sketch of a cart moving to the right while slowing down. Include an arrow for its motion and an arrow for the main horizontal force, with labels.