• Two balls that have the same mass, density and appearance, but made of different materials
• Compare elastic vs. inelastic
• Material type: Standard Neoprene and Norsorex

Happy and Sad Balls are used to show the relationship between elastic and inelastic collisions. While both balls share an identical makeup between mass, density, and appearance, one will bounce, while the other will not. They are sold as a pack of 10 pairs.

The Happy Ball consists of standard neoprene that has low hysteresis, low surface friction, and weak intermolecular forces. The Sad Ball consists of Norsorex that has high hysteresis, high surface friction, and stronger intermolecular forces.