Momentum and Energy


What plays the role of momentum in rotational motion?

The angular momentum of a rotating object is proportional to the product of its moment of inertia and its angular velocity. If there are no external torques on the object, then its angular momentum does not change.

An object with linear momentum that has no external forces on it cannot change its mass, so its velocity is constant. But a rotating object can change its moment of inertia, so, even without external torques, its rotational speed can be changed.

Put a toy gyroscope on a stand and spin the wheel. Gravity pulls down on the center of gravity of the gyroscope, creating a torque on the axis of rotation, causing it to rotate downward.

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