Newton’s Third Law



Newton’s Third Law

Preliminary Questions:

1. When a large truck collides head-on with a small car, the force that the truck exerts on the car is

a. less than the force exerted by the car on the truck.

b. equal to the force exerted by the car on the truck.

c. greater than the force exerted by the car on the truck.

2. When a large truck collides head-on with a car, how do the accelerations of the two objects compare? Ignore friction.

a. Truck accelerates less than car.

b. Truck accelerates more than car.

c. They have the same accelerations.

Procedure

We are going to explore the above questions directly, by measuring the forces exerted by two carts on one another. One cart will be heavier than the other, but the difference won’t be as much as the truck and the car.

You will be given two carts, each of which has a force sensor attached to it. There should be springs attached to the “measurement” end of each sensor, and these should be facing one another. Each cart will exert a force on the other cart by means of these springs, when they are in contact with each other. Make sure that the data rate of each force sensor is at least 100 Hz. One cart should have some extra weights placed on top of it.

I. First, examine a collision. Punch “start” on DataStudio, and project one cart gently toward the other. DataStudio will graph the two forces on the same scale. Stop the data collection after the collision, and compare the two forces. Comment on the forces: are they equal? Opposite?

Repeat this for a different initial speed to confirm that the results are reliable.

II. Now, place the two carts in contact with each other, and have someone push one cart toward the other end of the track, causing both carts to move. Again, measure the two forces. In this case, the forces will probably vary considerably, but should always be equal to each other. What does your data say?

Analysis

1. From your subjective observations, what can you say about the accelerations of the two carts during the collision? Were they equal? Explain

2. In part II, were the accelerations equal? Explain.

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