Frisbee flight
A Frisbee throwing disk flies straight only if you spin it. When we spin a Frisbee we generate angular momentum, which is conserved. Since it is conserved the Frisbee resists tilting, which would change the angular momentum, and so it tends to fly straight. However, giving a Frisbee angular momentum also takes energy. If I spin a Frisbee faster and so double its angular momentum, by what factor have I increased the rotational kinetic energy?
The answer is 4.
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1 solution
The angular momentum of a Frisbee is L = I ω where I is the moment of inertia and ω the angular velocity. If I double the angular momentum then the angular velocity also doubled. Since the kinetic energy is K = 2 1 I ω 2 this means the kinetic energy goes up by a factor of four.