Observations and results
Did the water balloon maintain its round shape as it was falling but then squash when it hit the ground? Did it then spring back into a round shape as it lifted back up off the surface?
When you lift up your water balloon, you are giving it potential energy—"potential" refers to something that could happen. (You have the potential to become a physicist, for example.) If something has potential energy, it has energy that's stored up. When you drop your water balloon, that potential energy becomes kinetic. Kinetic energy is the energy of motion. (A car moving at 100 kilometers per hour has a lot of kinetic energy.)
When the balloon hits the floor and stops, that kinetic energy has to go somewhere. The kinetic energy goes into squashing the balloon flat. When the balloon squashes, the rubber stretches—and stretched-out rubber wants to snap back to its original shape (think: a stretched rubber band). When the balloon’s stretched rubber snaps back, it pushes against the floor and the floor pushes back. As a result, the balloon goes bouncing back up in the air.
More to Explore
Gaining Height, from Exploratorium
Bouncing Balls, from Exploratorium
That's the Way the Ball Bounces, from Exploratorium
Follow the Bouncing Ball, from Exploratorium