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Chapter 6: MOMENTUM

EQ: How do momentum and impulse relate to one another?. Chapter 6: MOMENTUM. Momentum. a property of moving things means: inertia in motion momentum = mass  velocity p = mv units of momentum: kg·m/s. Momentum. Example:

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Chapter 6: MOMENTUM

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  1. EQ: How do momentum and impulse relate to one another? Chapter 6: MOMENTUM

  2. Momentum • a property of movingthings • means: inertia in motion momentum = mass  velocity p = mv units of momentum: kg·m/s

  3. Momentum Example: • A moving boulder has more momentum than a little stone rolling at the same speed. • A fast boulder has more momentum than a slow boulder. • A boulder at rest has no momentum. • more momentum = harder to stop or change direction of the object

  4. Impulse • the force and time (force  time) interval Impulse = Ft An impulse applied external to a system, produces a change in momentum Ft = Δmv Impulse = Change in momentum

  5. Impulse Changes Momentum The greater the impulse exerted on something, the greater the change in momentum.

  6. Impulse Changes Momentum • Case 1: increasing momentum • F and t • Apply the greatest force for as long as possible and you extend the time of contact. Examples: • Golfer swings a club and follows through. • Baseball player hits a ball and follows through.

  7. Impulse Changes Momentum • Case 2: decreasing momentum over a long time • Extend the time during which momentum is reduced • largetime interval produces smallforce. Examples: • Impact attenuators

  8. Impulse Changes Momentum

  9. Impulse Changes Momentum • Case 3: decreasing momentum over a short time • shorttime interval produces largeforce. Example: Karate expert splits a stack of bricks by bringing her arm and hand swiftly against the bricks with considerable momentum. Time of contact is brief and force of impact is huge. e:

  10. Bouncing Impulses are generally greater when objects bounce. Example: Catching a falling flower pot from a shelf with your hands. You provide the impulse to reduce its momentum to zero. If you throw the flower pot up again, you provide an additional impulse. This “double impulse” occurs when something bounces.

  11. TODAY’S ESSENTIAL QUESTION How is momentum conserved in collisions?

  12. law of conservation of momentum For all collisions in the absence of external forces, • net momentum before collision equals net momentum after collision. (net mv)before =(net mv)after

  13. Collisions Elastic collision • occurs when colliding objects rebound without lasting deformationor any generation of heat.

  14. Collisions Inelastic collision • occurs when colliding objects result in deformation and/or the generation of heat.

  15. More Complicated Collisions • Sometimes the colliding objects are not moving in the same straight line. • In this case you create a parallelogram of the vectors describing each initial momentum to find the combined momentum. • Example: collision of two cars at a corner

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