Happy Unhappy Balls - Happy Sad Balls

A dramatic comparison of elastic and inelastic collisions

The Happy / Unhappy Balls prove that even the simplest materials can deliver deep physics insights—often in the most surprising ways.

Side by side, these two black rubber spheres look nearly identical—but drop them, and the difference is unforgettable. One ball bounces wildly around the room, while the other just lies there no matter how hard you throw it. This dramatic contrast turns a simple action into a powerful lesson about energy transfer and collisions, making abstract ideas immediately visible and intuitive for students.

Why Teachers Love the Happy/Unhappy Balls

• Instantly memorable demonstration: The surprising difference grabs attention and sparks questions right away.
• Minimal setup, maximum impact: Just drop the balls—no sensors, stands, or calculations required.
• Perfect for predictions: Students quickly form hypotheses and test them repeatedly.
• Durable and reusable: Built for years of classroom use across grade levels.