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Chapter 8 Momentum. What is Momentum?. Momentum is mass x velocity for an object. Momentum = mv When direction is not important, Momentum = m x speed An object can have a large momentum if it has a large velocity, a large mass or both!. Example of Momentum. Momentum Non-Example.
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What is Momentum? • Momentum is mass x velocity for an object. • Momentum = mv • When direction is not important, Momentum = m x speed An object can have a large momentum if it has a large velocity, a large mass or both!
Example Problems • Which has more momentum: A ball with a mass of 1 kg rolling at 9.0 m/s or a ball with a mass of 3 kg rolling at 4.0 m/s? • Calculate the momentum of a 50 kg bowling ball rolling at 2 m/s.
8.2 Impulse Changes Momentum • The change in momentum depends on the force that acts and the length of time it acts. • The product of the force and the time interval during which it is applied is called the impulse. • Impulse = FΔt
How can you change the momentum of an object? • Combining the equations for momentum and impulse we get: FΔt = Δ(mv) so…changing the time of contact changes the impulse! • A car out of control – hits a haystack or a wall. Which is better? • The haystack has 100 times the contact time, reducing the impulse and therefore the force!
Examples of Decreasing the Force of Impact • Catching a ball – how? • Padded dashboard in a car – why? • Bungee jumping cord • Move away from a punch! • Drop a dish on the carpet – why?
Bouncing • The impulse required to bring an object to a stop and then to throw it back again is greater than the impulse required to just bring the object to a stop. • Karate Chop • Curved shaped water wheel
Conservation of Momentum • Law of Conservation of Momentum - In the absence of an external force, the momentum of a system remains unchanged.
Collisions • When objects collide without being permanently deformed or creating heat, the collision is said to be an elastic collision.
When objects collide and become permanently deformed or create heat, the collision is said to be an inelastic collision.