Happy and Sad Balls

This demonstration compares how different materials affect energy transfer in collisions. A "happy" ball made of neoprene rubber bounces high, showing an elastic collision, while a "sad" ball made of norbornene barely bounces, showing an inelastic collision.

1. Obtain a “happy” ball (neoprene rubber) and a “sad” ball (norbornene polymer).
2. Hold both balls at the same height.
3. Drop them simultaneously onto a hard surface.
4. Observe that the happy ball bounces high while the sad ball barely bounces.

Collisions Demo: Happy and Sad Balls - Physics Demos:

Happy & Sad Balls - SMU Physics:

📄 Happy & Sad Balls - SMU Physics: https://demos.smu.ca/demos/mechanics/139-happy-sad-balls

• Try dropping the balls from different heights to compare rebound behavior.
• Use additional balls made from other materials (e.g., steel, glass, plastic) to compare energy transfer.
• Roll the balls into a wall to observe horizontal collisions.

• If using heavy or very hard balls for comparison, caution is needed to prevent injury or damage.

• Why does the happy ball bounce higher than the sad ball? (Because less energy is lost to deformation and heat, making the collision more elastic.)
• What happens to the energy that doesn’t go into bouncing the sad ball? (It dissipates as heat, sound, and internal deformation of the material.)
• How does the coefficient of restitution describe these collisions? (It quantifies how much kinetic energy is conserved; a higher value means a more elastic collision.)
• Can a ball ever bounce higher than the height it was dropped from? (No, because that would require energy gain, which violates conservation of energy.)