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Quiz #1

Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine tomburbine@astro.umass.edu. Quiz #1. Momentum. Momentum is inertia in motion Momentum = mass x velocity Momentum = mv When you don’t care about direction: Momentum = mass x speed. Scalars and Vectors. Momentum.

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Quiz #1

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  1. Introduction to Physical ScienceMonday, Wednesday, ThursdayTom Burbinetomburbine@astro.umass.edu

  2. Quiz #1

  3. Momentum • Momentum is inertia in motion • Momentum = mass x velocity • Momentum = mv • When you don’t care about direction: • Momentum = mass x speed

  4. Scalars and Vectors

  5. Momentum • Moving object can have large momentum if it has a large mass, large velocity, or both

  6. To change momentum, you need to change the velocity or the mass of the object Momentum

  7. Momentum To change the velocity of an object, you need to apply a force, which accelerates an object

  8. Momentum The longer the force is applied, The greater the velocity changes, The greater the momentum changes

  9. Impulse Impulse = Force x time interval Impulse = Ft

  10. Questions: Compare the momentum of a 1 kg cart moving at 10 m/s with that of a 2 kg cart moving at 5 m/s. Does the moving cart have impulse? Does a moving cart have momentum? For the same force, which cannon imparts a greater impulse to a cannonball – a long cannon or a short one?

  11. Answers: Compare the momentum of a 1 kg cart moving at 10 m/s with that of a 2 kg cart moving at 5 m/s. Same momentum Does the moving cart have impulse? No. Impulse is something the cart experiences Does a moving cart have momentum? Yes For the same force, which cannon imparts a greater impulse to a cannonball – a long cannon or a short one? Long cannon. Force acts over a longer time

  12. Impulse and Momentum Impulse = change in momentum Ft = ∆(mv)

  13. Increase Momentum Increase the momentum of an object as much as possible, apply the greatest force as long as possible For example, a golfer and a baseball player will swing as hard as possible and follow through Following through extends the time of contact

  14. Exercise

  15. Decrease Momentum Why is it better to hit a haystack with a runaway car or a concrete wall to stop? You need the same impulse to stop the car

  16. Answer: • Why is it better to hit a haystack with a runaway car or a concrete wall if you want to stop? • You need the same impulse to stop the car • By hitting the haystack instead of the wall, you extend the time during which your momentum is brought to zero

  17. Decrease Momentum • Break bricks by a large impulse over a short time • http://www.youtube.com/watch?v=xwAu0KXTuj

  18. Law of conservation of momentum • In the absence of an external force, the momentum of a system remains unchanged • http://www.youtube.com/watch?v=UwWVEpjAIDg&feature=related

  19. Net Momentum Net momentum (before collision) = Net momentum (after collision)

  20. Types of collisions • Elastic collision – all the momentum is transferred to another object during a collision • Inelastic collision – Colliding objects become entangled

  21. Recoil Velocity of a gun • The recoil velocity caused by a gun exactly balances the forward momentum of the projectile • http://www.youtube.com/watch?v=X8imjiuOx1c

  22. Exercise

  23. Question: • If a freight car travelling at 10 m/s hits a car at rest hits another freight car with the same mass and the frieght cars become stuck together, what will be the velocity of the stuck cars?

  24. Answer: • If a freight car travelling at 10 m/s hits a car at rest hits another freight car with the same mass and the frieght cars become stuck together, what will be the velocity of the stuck cars? • (net mv) (before) = (net mv) (after) • (m x 10 m/s) = (2m x v) • v = 5 m/s

  25. http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_NextTime_Momentum.xmlhttp://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_NextTime_Momentum.xml

  26. Homework

  27. http://www.youtube.com/watch?v=DI3rPT_9rW0

  28. http://www.youtube.com/watch?v=DYMTAZrKLcM

  29. Any Questions?

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