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Physics 101 General Physics Who am I? Dr. Bruton I may be teaching the remainder of this course for Mr. Carlton. We have similar teaching styles. There will be extra credit. I will “teach to” Mr. Carlton’s test. I will hit the highlights of the chapters with PowerPoint presentations. Let’s take notes… Chapter 6 Momentum Momentum and Collisions This chapter is concerned with inertia and motion. Momentum helps us understand collisions. Momentum and Collisions Elastic Collisions – objects rebound – e.g. superball Inelastic Collisions – object stick together an usually become distorted and generate heat – e.g. clay ball 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 P = mv – High velocity bullet P = mv Impulse In order to change the momentum of an object you must apply a force over some time interval. Impulse = Force time interval = Ft Impulse and Momentum Impulse = Change in Momentum = Final (mv) - Initial (mv) F t = D(mv) Case 1: Increasing Momentum – Apply a force for a long time. – Examples: • Follow through on a golf swing. • Pushing a car. F Dt Case 2: Decreasing Momentum – Apply a force for a long time. – Examples: • • • • Air bags in cars. Catching an egg. Boxing, Figure 6.6 Soft collisions, Figure 6.3. F Dt Case 3: Decreasing Momentum – Apply a force for a short time. – Examples: • Boxing • Karate F Dt Conservation of Momentum This means that the momentum doesn’t change. Recall that F t = D(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 Example Problems...