Chapter 9Momentum and Its Conservation

9.1 Impulse and Change in Momentum

Momentum is used a lot, but it has a special meaning in physics. Newton wrote his three laws in terms of momentum, quantity of motion.

Momentum and Impulse

Momentum is the product of mass and velocity. It’s a vector with the same direction as the velocity, the unit is kg*m/s.

Momentum = mv

F = ma = mv/t Multiply both sides by t, F t = m v. Left side of equation is impulse, which is a vector in the direction of F, the unit is N*s.

If m is constant, v results in p.

p = mv

Ft = m v p Ft = p

This is the Impulse-Momentum Theorem which is a restatement of Newton’s 2nd Law.

Ex Pr 203-4 Prac Prob 204-5

Angular MomentumProduct of an objects mass, velocity and distance from center of rotation. No net torque, then angular momentum is constant. Angular momentum around the sun is constant; therefore, when planets distance from the sun is longer, the velocity is smaller. This is Kepler’s 2nd Law.

Summary9.1 Impulse and Change in

MomentumThe momentum of an object is the product of its mass and velocity. The change in momentum of an object is equal to the impulse that acts on it. Impulse is the product of the average force and the time interval over which the force acts.