The first thing that came to mind when thinking about a situation would be someone jumping on a trampoline. When identifying the forces that cause the motion to occur, there are a few. Gravity is the biggest one; gravity is what pulls you back down to the ground when you jump into the air. The force of your body would be another motion that occurs. Gravity pulls your body back down, and the force of your body results in putting tension on the spring and throwing you back into the air. Newton's third law is that for every action there is an equal and opposite reaction. When you fall back down into the trampoline mat, it then springs you back into the air, causing there to be a reaction with an equal and opposite force