Have you ever seen a rubber ball thrown it at the ground to see if it would bounce?
Well this time only one of the two balls will bounce back up into your hand. Can you guess which one it will be?
Both balls are the same size and color, approximately the same weight, feel the same and are nearly indistinguishable.
But drop them on the ground and only one bounces.
This concept was taken almost directly from one of my own childhood toys
This toy relies on the varying properties of different materials, most notably elasticity and although children may not be able to fully understand why one ball bounces and the other doesn't, it will teach them that despite the fact that two things appear to the same, they will not always act as such.