A skater spinning with arms outstretched pulls the arms inwards. The result is that
Correct answer: A. the angular speed increases, because the moment of inertia decreases and angular momentum is conserved
- A. the angular speed increases, because the moment of inertia decreases and angular momentum is conserved
- B. the angular speed decreases
- C. the angular momentum increases
- D. nothing changes
Explanation
With no external torque the angular momentum, the product of moment of inertia and angular speed, stays constant, so reducing the moment of inertia must raise the angular speed. The skater's rotational kinetic energy actually increases, and the extra energy comes from the muscular work done pulling the arms in against the outward tendency. The same principle explains the spin of a collapsing star.
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About Angular Velocity
Angular velocity describes how quickly angular displacement changes with time, with ω = Δθ/Δt and units of radians per second. Questions relate angular and linear motion through v = rω, use the direction given by the right hand rule, and distinguish angular velocity from angular acceleration and ordinary frequency.
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