Stable and Unstable Spins

Bullets, spacecraft and a flipping nut

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Spin stabilises bullets, footballs and spacecraft.
• Rotation about the intermediate axis is unstable (tennis racket theorem).
• With energy loss, objects end up spinning about their axis of largest moment of inertia.

Steps

1. Rifling
2. The tennis racket theorem
3. Losing energy, keeping spin
4. Spinning bullets
5. The flipping axis
6. Which axis is stable for a satellite?