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Momentum and impulse

Momentum and impulse. What is Momentum??? What is Impulse???. What has more Momentum?. A civic going down the highway at 30 mph or a semi going the same speed? A civic going 30 mph or a civic going 60 mph? A civic going 5 mph or a semi parked along the road?

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Momentum and impulse

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  1. Momentum and impulse What is Momentum??? What is Impulse???

  2. What has more Momentum? • A civic going down the highway at 30 mph or a semi going the same speed? • A civic going 30 mph or a civic going 60 mph? • A civic going 5 mph or a semi parked along the road? • What factors do you think affect the momentum of something?

  3. MOMENTUM • MOMENTUM IS: • Proportional to both mass and velocity • p • A vector quantity • SI Units: kg • m/s p = mv Momentum = mass x velocity

  4. Conservation of Momentum • The total momentum of a system remains constant unless acted on by an outside force! • http://www.youtube.com/watch?v=DF4hdDXSg-o&feature=related • http://www.youtube.com/watch?v=rKsaHMBjuTc • http://www.youtube.com/watch?v=oN0idQZw-Ao • http://www.youtube.com/watch?v=prpidlpBNsA

  5. Momentum and Newton’s 2nd Law • Prove that the two equations shown below are equivalent. • F = ma and F = p/t • Newton actually wrote his 2nd Law as F = p/t. • Force depends on how rapidly the momentum changes.

  6. The quantity Ft is called impulse. SI units: N•m or kg•m/s Impulse equals change in momentum. Another version of Newton’s 2nd Law Changes in momentum depend on both the force and the amount of time over which the force is applied. Impulse and Momentum

  7. Egg in Blanket Demo: • How does the change in momentum in both cases (smashed and saved) compare? • Why is the egg saved in the blanket? (which variable is affected?) • Why is the egg smashed on the floor (which variable is affected?)

  8. Ft = p = mv • When stopping, p is the same for rapid or gradual stops. • Increasing the time (t) decreases the force (F). • What examples demonstrate this relationship? • Air bags, padded dashboards, trampolines, etc • Decreasing the time (t) increases the force (F). • What examples demonstrate this relationship? • Hammers and baseball bats are made of hard material to reduce the time of impact. Stopping Time

  9. Change in momentum • Greater changes in momentum(p) require more force (F) or more time (t) . • A loaded truck requires more time to stop. • Same stopping force • Greater p for truck with more mass

  10. CRASH!!! These two cars both get into an accident with the same initial conditions and this causes both cars to stop abruptly.What safety features does the newer model have and how do they work to keep the passengers/car safe? Car from 1960’s Car from 2008

  11. A 65 kg passenger in a car travels at a speed of 8.0 m/s. If the passenger is stopped by an airbag in 0.75 s, how much force is required? • Answer: 6.9 x 102 N • If the car does not have an air bag and the passenger is instead stopped in 0.026 s when he strikes the dashboard, by what factor does the force increase? • Answer: F = 2.0 x 104 N so it is 29 times greater Practice OnE

  12. PRACTICE TWO • A 1350 kg car has a velocity of 22.0 m/s to the north. When braking rapidly, it stops in 4.50 s. • What was the momentum of the car before braking? • What is the magnitude of the force required to stop the car? • Answers: • 2.97 x 104 kg • m/s to the north • 6.60 x 103 N

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