Chapter 5 Momentum

Momentum and Collisions This chapter is concerned with inertia and motion. Momentum helps us understand collisions. Elastic Collisions - objects rebound Inelastic Collisions - object stick together an usually become distorted and generate heat

Momentum Momentum = mass  velocity p = mv Momentum is a vector quantity.

A large truck has more momentum than a car moving at the same speed because it has a greater mass. Which is more difficult to slow down? The car or the large truck? Large Momentum Examples: –Huge ship moving at a small velocity –High velocity bullet

Impulse In order to change the momentum of an object you must apply a force over some time interval. Impulse = Force  time interval = F t

Impulse and Momentum Impulse = Change in Momentum = Final (mv) - Initial (mv) F t =  (mv)

Case 1: Increasing Momentum –Apply a force for a long time. –Examples: Follow through on a golf swing. Pushing a car. Case 2: Decreasing Momentum –Apply a force for a long time. –Examples: Boxing, Figure 5.6 Air bags in cars. Soft collisions, Figure 5.3. Catching an egg. FtFt FtFt

Case 3: Decreasing Momentum –Apply a force for a short time. –Examples: Boxing Karate FtFt

Conservation of Momentum This means that the momentum doesn’t change. Recall that F t =  mv) In this equation, F is the "external force". Internal forces cannot cause a change in momentum.

Examples Conservation of Momentum: If there are no external forces, the total momentum for a system remains unchanged. Example 1: a person sitting inside a car pushing against the dashboard Example 2: a bullet fired from a rifle Example 3: a rocket is space

End of Chapter 4