In this activity, students make a Tin Can Toy with a secret mechanism, while exploring kinetic energy. When you roll a Tin Can Toy away, it comes rolling back!
Adapted from GEM this Tin Can Toy made of a coffee can contains a simple elastic powered motor. The "secret" to the Come-Back Can is in the weight that hangs from the rubber band.
The weight in the Tin Can Toy hangs down as the tin rolls in one direction (and doesn't flip). The kinetic energy of the rolling can will be stored as potential energy in the tightly twisted rubber band -some will not be stored as the rubber band is wound, but transferred to friction (heat) and sound.
Once the band has reached its storage limit, the stored energy is released and the Come-Back Can moves backwards towards its starting point.