What forces act on a mousetrap car?

A moving mousetrap car is affected by two type of friction: airfriction and bearing friction. Airfriction is a large factor only with cars that are moving fast and is nearly negligible for slow-moving distance cars; therefore, in this lab you will only take bearing friction into consideration.

How does Newton's 3rd law apply to a mousetrap car?

Newton's third Law states that for every action there is an equal and opposite reaction. As the mousetrap car moved across the floor, gravity was pushing it down and the car was pushing the floor up also, car pushes floor backward, floor pushes car forward.