chapter6.1-6.3_slides

# chapter6.1-6.3_slides - Chapter 6 Momentum and Collisions...

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10/4/2009 1 Chapter 6. Momentum and Collisions v m P : Momentum t F I : Impulse f i P P : momentum of on Conservati What is common among these sports? We hit the ball, and it flies off Physics: An impulse of force acts on the ball so it gains momentum What is momentum? and What is impulse?

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10/4/2009 2 We learned in Ch5 that a moving object has certain energy, kinetic energy: Kinetic energy is related to the work done to the object A moving object also has certain momentum : SI unit: kg•m/s = N •s Momentum is related to the Impulse done on an object Both momentum and impulse are vector quantities and have the same units. 2 2 1 mv KE v m P KE x F W net net cos t F I Similar to the work-energy theorem, we have the impulse- momentum theorem: Proof: From Newton’s second law: t F I p I v m P i f v m v m p a m F ) ( t a m t F ) ( i f v v m t F p I t a v v i f Impulse=change in momentum
10/4/2009 3 We can rewrite the above to give - The rate of change in momentum of an object is equal to the force acting on it. Why airbag and seatbelt work: During a collision, the change in momentum is fixed you cannot change it. - Initial momentum - Final momentum To minimize the injury ( reduce the force acting on the person’s body), the only thing we can do is to increase the collision time p t F F t p i i v m p 0 f f v m p p t F Which of the following is a valid unit of momentum (1) Newton•second (N•s) (2) kg•m 2 /s 2 (3) Newton•meter ( N•m )

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10/4/2009 4 Often the force acting on an object is not constant, the time could be very short or very long The impulse-momentum still holds Need to replace the force with an average force Very Short time Very long time p t F av Work-energy theorem KE x F W x 2 2 1 mv KE KE KE KE i f Impulse-momentum theorem p t F I v m p p p p i f Unit of energy, work Kg• m 2 /s 2 = N •m Unit of momentum/impulse Kg• m/s = N • s
10/4/2009 5 Momentum: , a vector quantity Magnitude of momentum: , a scalar quantity Kinetic energy (a scalar) v m P mv P m p m v m mv KE 2 / 2 1 2 1 2 2 2 2 m p KE 2 2 A golf ball of mass 5x10

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## This note was uploaded on 01/02/2010 for the course PHY 101 taught by Professor Pralle during the Spring '08 term at SUNY Buffalo.

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chapter6.1-6.3_slides - Chapter 6 Momentum and Collisions...

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