Angular Momentum
Definition
The rotational equivalent of momentum — a measure of how much ‘spin’ an object has, combining its mass, speed, and distance from the rotation axis.
Symbol: · Unit: kg·m²/s
Technical definition
For a point mass, L = r × p (position cross linear momentum), with magnitude L = rmv·sinθ. For rigid bodies, L = Iω. In the absence of external torque, total angular momentum is conserved.
Example
A figure skater spins faster when pulling arms in: reducing the moment of inertia I forces angular velocity ω to increase so that L = Iω stays constant.
Common confusion
Angular momentum is not the same as angular velocity. Two objects can spin at the same rate but carry very different angular momentum if their masses or sizes differ — like a bicycle wheel versus a truck tire at the same rpm.