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Spinning skater and diver
Beginner
Tucking in reduces I and raises ω.
Pulling limbs in reduces I, increasing ω. Rotational kinetic energy rises since the person does work.
Diver tucks: 3 rotations in under 2 s.
No external torque during flight.
In more detail
Spinning skaters and divers conserve angular momentum. Pulling the arms or legs in reduces the moment of inertia and increases the spin rate, while extending them slows the spin.
Real-world uses
- Figure skating pirouettes are controlled by arm position.
- Divers tuck in to spin faster for multiple somersaults.
- A figure skater, a diver and an ice dancer all use the same rule: pulling limbs in speeds up the rotation.
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Frequently asked questions
How do divers stop spinning?
They extend their bodies, increasing the moment of inertia and slowing the rotation.
Does it take energy?
Yes. Muscular work is needed to change the body's shape.
Does it take energy to spin faster?
Yes. The skater does work by pulling in the arms, which increases the rotational energy while angular momentum stays the same.
Related topics in Rotational Motion
Angular momentum of rigid body · Torque and angular momentum · Conservation of angular momentum · Collisions in rotation · Precession of a gyroscope · Nutation