Rolling and Unrolling

Energy split, yo-yos and bowling balls

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Rolling splits kinetic energy between translation and rotation (2/7 rotational for a solid sphere).
• A yo-yo with a thin axle puts almost all its energy into spin and falls slowly.
• A sliding ball ends up rolling at 5/7 of its starting speed (angular momentum about the contact point).

Steps

1. Two kinds of motion
2. Every point of a rolling wheel
3. The spinning share
4. Slow the yo-yo
5. A rolling hoop
6. Skid, then roll
7. Five-sevenths