PRODUCT TYPE: Trinket
These two black, rubber balls look and feel very similar. But they are made out of materials that behave very differently. Drop them on the floor and one will bounce (the "happy" ball) and one will not ( the "sad" ball). This is due to the difference in hysteresis.
The happy ball is made from polychloroprene (Neoprene) and the sad ball is made from polynorbornene (Norsorex). These materials differ in hysteresis, which is a measure of how long it takes them to return to their original state after a change.