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Angular momentum
Intermediate
Rotational analogue of momentum.
L = r×pL = r × p measures the amount of rotation about a point. For a particle in a circle L = mvr and for a rigid body L = Iω.
1 kg at 2 m/s on a 3 m radius: L = 6 kg·m²/s.
Angular momentum depends on the chosen origin.
In more detail
Angular momentum is the rotational analogue of linear momentum, L = Iω for a rigid body, or r × p for a particle. It is conserved in the absence of external torques.
Real-world uses
- Spinning tops and gyroscopes keep their orientation because of angular momentum.
- Planets keep their spin because of conserved angular momentum from their formation.
- A spinning top or a planet orbiting the Sun carries angular momentum, which depends on its position and linear momentum.
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Frequently asked questions
What are the units?
Kilogram metres squared per second.
Is angular momentum a vector?
Yes. Its direction is along the axis of rotation, given by the right-hand rule.
Is angular momentum a vector?
Yes. It points along the axis of rotation, given by the right-hand rule.
Related topics in Momentum & Collisions
Thrust · Multi-stage rockets · Jet and conveyor problems · Conservation of angular momentum · Ice-skater spin · Kepler's second law from L