The Amazing Returning Rod

In this activity, a metal rod can be made to roll back to you automatically when pushed away. What's at work behind the phenomenon?

Not only will this activity encourage critical thinking as your child tries to figure out what happened, it will also serve to reinforce the physics concept of stored energy!

What You Need:

• large metal coffee can with a lid that clips into the top
• electric drill
• long elastic rubber band
• string
• small weight

What You Do:

1. Drill two holes in the lid of the tin, about 50 mm apart, and two matching holes in the base of the can.
2. Thread the elastic rubber band through the base holes, and also through the holes in the lid, and tie the ends. Then tie the two sides of the rubber bands together with the string, and use the string to tie the weight tightly to the elastic.
3. Take the two ends of the elastic rubber bands up through the lid holes, put the lid on the can, and tie off the two ends.
4. Roll the can away from you: this should "wind up" the elastic bands, causing the can to roll back again.
5. The rolling can stores energy in the elastic rubber band, because the weight always hangs down as the can rolls in one direction. Have your child try making a second one in a clear plastic container, to see how it works.