"ELI5: Angular Momentum"

Jarod Smith, a member of the COSI on Wheels team, asked me for help in crafting a quick-and-easy way to explain conservation of angular momentum to young kids, and more importantly sometimes to their parents.

The topic comes up in a fun and simple demo. Sit on a chair that can rotate, and hold a spinning bicycle wheel in your hands. Flip the wheel over and presto-chango you start spinning in your chair. Magic! I mean, science!

I like to think of momentum as the amount of "oomph" an object has - how much it can pack a punch if it were to hit you. A small object (like a bullet) traveling fast enough can hurt, and a big object (like a truck) can be a pain pretty much no matter how fast it's going.

Angular momentum is then oomph going in a circle. It's conserved, which means the total amount of oomph must be the same.

For very young kids, I just refer to it as spin. The bicycle wheel in your hands is spinning really fast in one direction. That's the total amount of spin that you+wheel can have. When you flip the wheel over, you're taking away the spin in that direction, so some has to be added: you yourself start spinning to compensate.

Ultimately, while we can explain what's going on as best we can, I think in some cases it's sufficient to let the demo do the talking. Kids are developing an intuitive sense of angular momentum conservation, and that's something we can build on when they're older.