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What We Know About Momentum…

What We Know About Momentum…. The product of an object’s mass and velocity. ρ = mv Units are kg x m/s Why isn’t m or M used for the symbol of momentum?. Very Important: In order for an object to have momentum it must…………. ..........................be moving!

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What We Know About Momentum…

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  1. What We Know About Momentum… • The product of an object’s mass and velocity. • ρ = mv • Units are kg x m/s • Why isn’t m or M used for the symbol of momentum?

  2. Very Important: In order for an object to have momentum it must…………..

  3. ..........................be moving! If you are asked to give an example of something with a lot of momentum and your response is a bullet, or a mack truck, or an NFL linebacker, you are WRONG!

  4. Changing momentum can be done two ways. • A momentum change can take place over a long period of time: • FΔt • Or over a short period of time: • FΔt

  5. Example: Changing the Momentum of a Thrown Egg • Egg mass = .056 kg velocity= 9 m/s p = ___________ Over a Long Period of Time: t = 0.9 s p = .504 kg X m/s F∆t = m∆v F(0.9s) = .504 kg x m/s F = .56 N Therefore, the egg does not break Over a Short Period of Time: t = 0.09 s p = .504 kg x m/s F∆t = m∆v F(0.09s) = .504 kg x m/s F = 5.6 N Therefore, the egg breaks

  6. In Summary: • For an object with a given amount of momentum t ↑ then F↓ t ↓ then F↑

  7. Other Examples: • Egg toss • Padded dashboard in the car • Air bags in the automobile • Baseball catcher • Jump from the table top (flex the knees) • Boxers “rolling with the punches” • Bungee Jumping • Stunt person off a building and into an air mat

  8. Collisions • There are two types of collisions that we will discuss in class. In one, the objects bounce off of each other and in the second, the two collide and then stick together.

  9. Two Types of Collisions • Elastic- two objects collide and return to their original shapes with no change in total kinetic energy. • “bounce” away from each other • Billiard balls, glass balls colliding are nearly elastic • Key Words: bounce, hit and recoil • Inelastic- occurs when two objects collide and move together as one mass, like two railroad cars coupling. • momentum is still conserved, but there is some energy “lost” • Key Words: stick together, couple, become embedded

  10. The Collision Formula, also known as the Law of Conservation of Linear Momentum • m1v1 + m2v2 = m1v1΄ + m2v2΄ If they stick together, then v1΄ and v2΄ are the same making the formula look like this: m1v1 + m2v2 = ( m1 + m2 ) v ΄ Or, Mobefore = Moafter

  11. The Law of Conservation of Momentum • In the absence of an outside force, the momentum of a system remains unchanged. In other words, the momentum before equals the momentum after.

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