Materials:
- basketball
- hard floor or pavement to bounce ball on
Activity:
To demonstrate gravitational potential energy, hold a basketball over your head and release it on to the pavement. Gravity pulls the ball towards the Earth creating kinetic energy as it drops until it hits the pavement converting it back to potential. This conversion from potential to kinetic is repeated as the ball bounces up and down the pavement.
When you drop the ball, note how high it bounces back. Why doesn’t it bounce back to the same height at which you let it go? If you let the ball keep bouncing, notice that with it bounces back a little lower each time.
If the ball were to bounce back to the same height at which it was dropped, that would mean all the gravitational energy was converted to kinetic energy. It isn’t all movement, though is it? Listen (that’s a hint), what other forms of energy can you detect or identify? Think back, too, to the rubber band experiment–can you think of another energy form?
Check out SnapShot Science’s ball bouncing experiment!
2. Roll-back Toy
Materials:
- A small container that can be laid on its side and rolled and have a hole punched in its top and bottom (such as a clear plastic soda bottle or coffee can)
Note: Using a clear soda bottle helps to demonstrate what is happening inside.
- One thick rubber band about 3-4 inches long (8-10 cm)
- Two tooth picks or paper clips
- Several washers tied together with a twist tie or another weighting device that will fit through the opening of a soda bottle or the container being used.
- String
- Hole punch tool or scissors
Procedure:
Punch a hole through the lid and the bottom of the container. Take the lid off the container. Thread a string through the bottom of the container and pull it through the lidless top of the container (make sure there is still string hanging out the bottom end).
Tie the end of the string that you pulled through the top to one end of the rubber band (you will use the string as a lead to help thread the rubber band through the container).
Tape the washers together and then connect them to the middle of one section of the rubber band (do not tape the strands of the rubber band together).
Put the end of the rubber band (the end not connected to the string) through the container lid. Use a toothpick to secure the band so that it does not slip inside the container (put the toothpick through the end loop of the rubber band that remains outside the hole). Put the lid on the container (making sure the string is still sticking out the other end).
Carefully pull on the thread until the rubber band comes through the hole. Secure the band with the second tooth pick. Be sure to situate the weight so it is in the center of the container and does not touch the sides. Your roll-back toy is ready to go!
Activity:
Roll the toy and watch as the weight holds one strand of the rubber band stationary while the free side twists around. The farther the toy is rolled the more potential energy. Release and watch the toy roll back towards you demonstrating kinetic energy. This would be a great activity to have races in the classroom to see who could devise the roll-back toy with the greatest potential energy.
Check out this Physics Project: Rollback Can