Spinning Ball Bearings

We think that this physics toy was around at least 100 years ago. It is a nice demonstration of energy conversion.

Just as a child on a swing is converting potential energy (at the highest point of the swing) to kinetic energy (at the lowest point of the swing) and back again, this toy works in a similar way.

Two ball bearings give the best results, because of they are heavy. These two metal balls are less heavy, and actually have little bells inside. Nevertheless they demonstrate the principle to some extent. The two balls are connected by elastic, and you need to start by winding up the elastic. Then place the toy on a smooth, flat surface, and as the elastic unwinds, the two balls spin round, gaining speed.

As the balls continue to spin, the elastic unwinds, and then winds up again, the other way. When the two balls stop spinning in the original direction, they will now spin in the opposite direction.

With heavy ball bearings on a mirror surface, it is possible to get quite a few spins, first in one direction, and then the other.