Rotational Motion & Torque

Angular momentum, moment of inertia, and spinning objects

Torque is the rotational equivalent of force: τ = rF sinθ. The rotational equivalent of Newton's 2nd Law is τ = Iα. Angular momentum L = Iω is conserved when no external torque acts — this is why a spinning skater spins faster when they pull in their arms (reducing I increases ω to keep L constant). The moment of inertia I depends on how mass is distributed relative to the rotation axis.