Find the angular momentum of an orbiting or rotating point mass with L = m·v·r — or solve for mass, velocity or radius. Choose your own units for each input.
Angular momentum measures the rotational motion of a mass about a point. For a point mass it is L = m v r — mass times its speed times its distance from the axis (for velocity perpendicular to the radius).
Angular momentum is conserved when no external torque acts, which is why a spinning skater speeds up as they pull their arms in (smaller r means larger v) and why planets sweep out equal areas in equal times.
For a point mass, L = mvr — mass times velocity times radius. For an extended rotating body it is L = Iω, the moment of inertia times angular velocity.
Kilogram metres squared per second (kg·m²/s), equivalent to joule-seconds (J·s).
In the absence of an external torque, total angular momentum stays constant. This is why a skater spins faster when pulling their arms in — reducing r increases v to keep L fixed.
Linear momentum (p = mv) describes straight-line motion; angular momentum (L = mvr) describes rotation about a point and additionally depends on the distance from the axis.