# Lect_18 - Momentum and Newton's Second Law Lecture 18...

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Lecture 18 Linear Momentum and Impulse Momentum and Newton’s Second Law a m F G G = net () dt v d G = G = p G = G G Linear momentum Newton’s second law in terms of linear momentum: G G = net A net force is a transfer of linear momentum. net Fdt ∆= G G Impulse The change in linear momentum for a certain time interval is called the impulse J (something like “how much of an effect did the force have by being applied during a given time interval ”). 0 net f t Jp =∆ = GG G | | = area 0 f Equal area average average Ft =∆ G average tt == G G G dp  =   G G Short-duration collision, large maximum force. eg. Hitting a hard ball with a bat Long-duration collision, small maximum force. eg. Hitting a soft ball with a bat Same impulse Same change in momentum

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Units of Momentum and Impulse SI units kg m/s v m p G G =∆ = GG G net JpF d t N s It’s the same! ACT: Egg tossing In an egg-tossing contest, two people toss a raw egg back and forth. After each successful toss, each person takes a step back. Catching the egg without breaking it becomes harder and harder. Usually the trick is moving your hand down with the egg when you receive it. This works better because: A. It decreases the change in momentum. B. It decreases the impulse. C. It decreases the force on the egg. • If the flying egg has speed , the change in momentum is: p = 0 – mv = - (independent of how you catch it) • The impulse is just the same!
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Lect_18 - Momentum and Newton's Second Law Lecture 18...

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