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Momentum

Momentum. Momentum. inertia and motion Newton’s “quantity of motion” helps us understand collisions and explosions. Momentum and Collisions. Elastic Collisions objects rebound e.g. superball Inelastic Collisions object stick together an usually become distorted and generate heat

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Momentum

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  1. Momentum

  2. Momentum • inertia and motion • Newton’s “quantity of motion” • helps us understand collisions and explosions

  3. 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

  4. Momentum • Momentum = mass ´ velocity p = mv • Momentum is a vector quantity.

  5. 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?

  6. Large Momentum Examples: • Huge ship moving at a small velocity • High velocity bullet P = mv P = mv

  7. 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

  8. Impulse and Momentum • Impulse = Change in Momentum • = Final (mv) - Initial (mv) • F t = D(mv)

  9. Case 1: Increasing Momentum • Apply a force for a long time. • Examples: • Follow through on a golf swing. • http://www.youtube.com/watch?v=Xy9GTAENiJA • Pushing a car. FDt

  10. Case 2: Decreasing Momentum • Apply a force for a long time. • Examples: • Air bags in cars. • http://www.youtube.com/watch?v=nlWJayKWvw0 • http://www.youtube.com/watch?v=_Av0WGrlTGY • http://www.youtube.com/watch?v=D-ogrMr4lWc • Catching an egg. • Boxing, Figure 6.6 • Soft collisions, Figure 6.3. FDt

  11. Case 3: Decreasing Momentum • Apply a force for a short time. • Examples: • Boxing • Karate • http://www.youtube.com/watch?v=jttqJZ9sTBk FDt

  12. 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.

  13. 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

  14. Conservation of momentum • The total momentum of a group of interacting objects remains the same in the absence of external forces • Applications: Collisions, analyzing action/reaction interactions

  15. Question • Which has more momentum? • (A) A parked cruise ship • (B) You in your vehicle driving home

  16. Question 1. A force times time is most appropriately called • (a) weight • (b) impulse • (c) velocity • (d) momentum

  17. Question 2. Suppose two freight cars of equal mass are coupled by a collision. This is an example of • (a) an elastic collision • (b) an inelastic collision • (c) none of the above

  18. Question 3. Which of the following is true about momentum? • (a) it is a vector • (b) it is a product of mass times velocity • (c) impulses are required to change it • (d) all of the above

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