Newton's Third Law

Block 6 Rebecca Harvey, Aleksi Arostegui
By: Rebecca Harvey

In this lab, we tested Newton's Third Law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body.

Part 1: Two Sensors and a Rubber Band

In this part of the lab, we used two force sensors with a rubber band between them and pulled. We first had one partner pull and one hold steady, then switched roles. After that, we both pulled at the same time. We recorded our data as follows. 

In this graph, Alek pulled on the sensor while I held still. 

In this graph, I pulled the sensor and Alek held still. 

In this graph, we both pulled at the same time.











Part 2: Scales and Rolling Chairs

In this part, we sat in rolling chars and pressed two scales against each other. First, we pushed each other and read the scales, which were both at 10 N. Alek started rolling backwards because the wheels on his chair had less friction with the ground than mine. Then, we had a third person push us together, and both scales in that case read 20 N.






Part 3: Collisions

In this part, we had a cart with a sensor on it moving towards another sensor. We rolled the cart slowly at first, the with more force. Both sensors read the same amount of force no matter how hard we did it.








Part 4: Colliding Carts with Rings

In this part, there were two videos of two carts bouncing off of each other using stretchy rings as buffers. In both videos, the rings bent exactly the same amount. In the first one, where both carts had nothing on them, both carts hit each other and bounced back with the same force, with both rings at the same degree of bendiness. In the second one, one of the carts was weighed down with a books. The rings still bent at the same angle, but the heavier cart moved backward less that the unladen cart did. This shows that while the forces were equal when the carts collided, the force was more effective in moving the lighter cart.

Summary: In all these different experiments, we learned that the forces of two objects interacting are always equal, no matter whether they are moving, at rest, pushed, pulled, or anything in between. As long as two objects are touching, the force between them is the saem.