This is me demonstrating as many of the principles we learned this quarter as I can.  In this picture the ball has velocity, acceleration, speed, displacement, position, and probably some other stuff that I haven't thought of.  Anyway, because we now know all these cool things about physics, bouncing the ball up and down on a tennis racquet becomes much more interesting.  I now know that if I hit the ball towards the ground, it would hit the ground at the same speed as a ball I hit upwards with the same velocity.  I also know that if, for example, I hit the ball upwards at 20 m/s, the velocity of the ball leaving my racquet would be the same as the velocity of the ball just before it returns to my racquet.