10/21/10

Post date: Oct 21, 2010 3:51:21 PM

Bell Ringer: What is momentum?

• • 9.1 Notes (PowerPoint)

    • 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

      • p = mv practice problems on overhead (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