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chapter06 - Chapter 6 Momentum and Collisions Momentum The...

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Chapter 6 Momentum and Collisions
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Momentum The linear momentum of an object of mass m moving with a velocity is defined as the product of the mass and the velocity SI Units are kg m / s Vector quantity, the direction of the momentum is the same as the velocity’s p v m p v
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More About Momentum Momentum components p x = m v x and p y = m v y Applies to two-dimensional motion Momentum is related to kinetic energy 2 2 p KE m
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Impulse In order to change the momentum of an object, a force must be applied The time rate of change of momentum of an object is equal to the net force acting on it Gives an alternative statement of Newton’s second law ( ) f i net m v v t t p F
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Impulse cont. When a single, constant force acts on the object, there is an impulse delivered to the object is defined as the impulse Vector quantity, the direction is the same as the direction of the force t I F I
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Impulse-Momentum Theorem The theorem states that the impulse acting on the object is equal to the change in momentum of the object If the force is not constant, use the average force applied f i t m m I F p v v
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Average Force in Impulse The average force can be thought of as the constant force that would give the same impulse to the object in the time interval as the actual time-varying force gives in the interval
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Average Force cont. The impulse imparted by a force during the time interval Δt is equal to the area under the force-time graph from the beginning to the end of the time interval Or, the impulse is equal to the average force multiplied by the time interval, av t F p
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Impulse Applied to Auto Collisions The most important factor is the collision time or the time it takes the person to come to a rest This will reduce the chance of dying in a car crash Ways to increase the time Seat belts Air bags
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Typical Collision Values For a 75 kg person traveling at 27 m/s and coming to stop in 0.010 s F = -2.0 x 10 5 N a = 280 g Almost certainly fatal
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Survival Increase time Seat belt Restrain people so it takes more time for them to stop New time is about 0.15 seconds
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Air Bags The air bag increases the time of the collision It will also absorb some of the energy from the body It will spread out the area of contact Decreases the pressure Helps prevent penetration wounds
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Conservation of Momentum Momentum in an isolated system in
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