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Unit 2Lesson 2

Motion and Force

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Lesson 2 Key Question

Example: Consider giving a low-friction cart a quick shove along a track.

When an object is moving, does this mean there must be a force pushing it in the direction of its motion?

PART 1

Giving Cart a Quick Shove

After your shove, as it moves along the track, is there still a force pushing the cart forward?

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CQ 2-1: In the discussion between three students about the force acting on the cart after the quick

push, whom do you agree with?

A. Samantha

B. Victor

C. Amara

D. None of them

PART 1

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Force and motion simulator

PART 2

• Highlight the sections of the graph where the hand was pushing the cart forward.

• Between your marked sections do you think there was still a force pushing the cart forward? Why do you think so?

Look at the simulator speed-time graph of a cart being given some quick pushes as it moves along a track.

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CQ 2-2: Which force-time graph best represents your thinking about the force pushing the cart forward as it

moves along the track?

A. Graph A

B. Graph B

C. Graph CPART 2

A B C

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What does the simulator show?

PART 2

Watch a movie of the simulator being run.

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What does the simulator show?

PART 2

Which of the force-time graphs in CQ 2-2 looks most like the simulator result?

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Force and motion

• During the periods when the simulator cart was being given a shove, was there a force pushing it forward?

• What action in the real world do these simulator shoves correspond to?

• During the periods in between the simulated shoves was there a force pushing the cart forward?

PART 3

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Summarizing Questions• While the simulator cart was moving along the track,

was there a force pushing the simulator cart forward the whole time or only at certain times?

• During a contact push/pull interaction, what do you think is transferred from the source to the receiver: energy, force, both, or neither?

• During the periods while the cart was being given a shove, its speed increased. In between these periods its speed remained constant. Why do you think the speed behaved differently during these periods?

Summarizing Questions

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CQ 2-3: Suppose the force-time graph for a simulator cart looked like this. Which of the speed-time graphs below could be produced by applying a single force in this way?

A. Graph A

B. Graph B

C. Graph C

A B C

Summarizing Questions

Unit 2 Lesson 2 Homework

Learn how force and energy analyses are related

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