What is angular momentum?
Answer
Angular momentum is the rotational analogue of linear momentum, given by L = Iω for a rotating body or L = r × p for a particle.
The working
Definition
Angular momentum measures the quantity of rotational motion of a body about an axis. For a particle it is L = r × p, the cross product of position and linear momentum.
For a rigid body
For a body rotating about a fixed axis, L = Iω, where I is the moment of inertia and ω is the angular velocity. Its SI unit is kg·m²/s.
Vector nature
Angular momentum is a vector directed along the axis of rotation, given by the right-hand rule.
Conservation
When the net external torque is zero, angular momentum is conserved; this is why a spinning skater speeds up on pulling in the arms.
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