4/1/09

Post date: Mar 31, 2009 12:2:4 AM

Bell Ringer: Use the impulse momentum theorem to explain how airbags help protect us in a car crash.

• • Time for questions, finish labs if needed

  • Review impulse-momentum equation and implications

    • If we're changing speeds (say, from a high speed to a stop) our change in momentum will be the same no matter what force or time is used to accomplish that.

    • Very high forces can be hazardous to our health!

    • These high forces occur when the time is very small. Many safety devices (especially in cars) aim to spread a stopping force over a longer period of time.

      • Air bags

      • Crumpling bumpers

      • Parachutes - remember, it's not the fall that kills you, it's the sudden stop at the end!

      • Spiderman and momentum video: http://www.youtube.com/watch?v=kuVpwjYgvgg

      • Neo catching Trinity - does more harm than good!

• Conservation of Momentum

  • • Newton's third law implies that in a collision, the total momentum will remain constant for a closed system

    • p initial = p final

• • Page 185: 5-8 due Thursday