chapter6 - Chapter6 Momentum r p r v thevelocity r r p = mv...

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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 r p v r m = p v r r
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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 r r
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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 r r I r
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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 = ∆ = ∆ = - r r r r r 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 r r
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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 
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chapter6 - Chapter6 Momentum r p r v thevelocity r r p = mv...

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