Book: # 1

     A spot moves vertically up and down in a motion similar to that of an object being repeatedly thrown upwards. The velocity and then the acceleration vectors are displayed along with the displacement of the spot. The acceleration vector does not change during the motion. 

With this film one can introduce the idea that the acceleration depends on the force acting on a body; the constant acceleration all the time - on its way up, at the top of its trajectory, and on its way down. This demonstration is simplified by not showing the "origin" or the final "fate" of the spot. Thus, the spot has already been projected upwards when we see it, and it has not yet been "caught" when it falls out of our vision. Imagine that we could see the spot "thrown" vertically and then "caught", how would the acceleration during these times compare in direction and magnitude to the constant downward acceleration during free fall?