Chapter 9

1. Chapter 9 Linear Momentum and Collisions Dr. Jie Zou PHY 1151G Department of Physics

2. Outline • Linear momentum • Impulse • Momentum-impulse theorem Dr. Jie Zou PHY 1151G Department of Physics

3. Linear Momentum • Definition of Linear Momentum, p: • Linear momentum p is defined as the product of the mass m and velocity v of an object. • p = mv; SI unit: kg·m/s. • Momentum is a vector quantity. • Example: A 1180-kg car drives along a city street at 30.0 mi/h (13.4 m/s). What is the magnitude of the car’s momentum? • Using p = mv, we find p = (1800 kg)(13.4 m/s) = 15,800 kg·m/s. Dr. Jie Zou PHY 1151G Department of Physics

4. Impulse • Definition of impulse, I: • Impulse is defined to be the average force Fav times the length of application time, t. • I = Fav∆t; SI units: N·s = (kg·m/s2).s = kg·m/s, the same units as the units of momentum. • Impulse is a vector quantity. • Momentum-impulse Theorem: Impulse is the change in momentum. • I = Fav∆t = ∆p Dr. Jie Zou PHY 1151G Department of Physics

5. Example • A batter hits a ball, sending it back toward the mound. The mass of the baseball is 0.145 kg. The ball was approaching the batter with a speed of 90.0 mi/h and headed toward the pitcher at 60 mi/h after the batter hit the ball. If the ball and bat were in contact for 1.20 ms, what is the average force exerted by the bat? Dr. Jie Zou PHY 1151G Department of Physics

6. Homework • See online homework assignment at www.masteringphysics.com Dr. Jie Zou PHY 1151G Department of Physics