The quantity of rotation of a body, which is the product of its moment of inertia and its angular velocity.

• A. Linear Momentum
• B. Torque
• C. Angular Momentum
• D. Energy

Answer: (C)

Angular momentum describes how much rotation a body has. For rotation about an axis, the amount of rotational motion is measured by the product of the mass distribution and the spin rate: L = I ω. Here, I is the moment of inertia, telling how mass is spread relative to the axis (more spread-out mass means a larger I and makes it harder to spin), and ω is the angular velocity, how fast it’s turning.

The angular momentum vector points along the axis of rotation (direction given by the right-hand rule). A key relation is that only external torques can change it, with torque equal to the time rate of change of angular momentum (τ = dL/dt). Rotational kinetic energy, on the other hand, is 1/2 I ω^2, a different quantity.

So the product I ω captures the quantity that describes rotation itself—the angular momentum.