3/30/09

Post date: Mar 28, 2009 8:9:24 PM

Bell Activity: What is momentum?

• • Introduction to Momentum

    • If you are going to be hit by a ball...

      • Would you prefer it to move fast or slow?

      • Would you prefer a baseball or a bowling ball?

    • Momentum is a measure of how much tendency an object has to keep its motion

    • Momentum depends on the velocity of the object and it's mass

    • Equation for momentum: p = mv, or momentum = mass times velocity

    • Unit for momentum is kg*m/s, read "kilogram meter per second"

    • Example: The momentum of an 80 kg biker moving at 5 m/s is (80kg)*(5m/s) = 400 kg*m/s

  • Practice: Page 178, problem 1 (We will also do 2-4 later, and turn all 4 in)

    • p = mv practice problems on overhead due Tuesday (may also be found in "handouts" section of this web site)

  • Impulse-Momentum theorem

    • If a constant force is applied to something over a period of time, we call the product of force and time the impulse

    • If the mass of an object is constant, then the impulse is equal to the change in momentum of the object

    • Equation: Force x time = change in momentum or Force x time = mass x change in velocity

    • See page 177 for the symbols in this equation

    • Example: A baseball being hit by a bat (page 178)

    • Application question: Why are we taught to follow through when we swing a bat?

  • Practice: Page 178, problem 2-4

Page 178: 1-4 due Tuesday

p=mv problems due Tuesday