Inertia and Velocity • In the law of action we began with mass and acceleration • F = ma • This was generalized to use momentum: p = mv.
Moment of Momentum • To continue the analysis of rotational motion, we must also extend the idea of momentum. p r
Law of Angular Inertia • The time derivative of angular momentum is the net torque. • A net external torque causes a change in angular momentum.
Applying Torque • An external torque changes angular momentum. • dL/dt= t L L+rpsinq w w p
Spinning Mass • The moment of inertia is the analog of mass for rotational motion. • The analog for angular momentum would be: w
Conservation • With no external torque, angular momentum is constant. • dL/dt= 0, L = constant 4w w m r/2 r I = mr2 I = mr2/4 next