p140w07_ct_13 - Racquetball Striking a Wall Copyright:...

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Physics 140: Winter 2007 Lecture #13 February 15, 2007 Dave Winn Racquetball Striking a Wall Copyright: Loren M. Winters Mt. Etna Andrew Davidhazy
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Momentum • Momentum ( ) is a vector measure of motion • Its value is dependent of the direction of motion • For an object of mass m moving with velocity • Impulses, forces acting for some time, change momentum: • Momentum is conserved in all collisions v m p v r r r = p r p d dt F dt p d F r r r r = =
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A ball rolls without friction on a pool table with initial momentum p i as shown. I strike it with a sharp tap, after which it’s momentum is p f as shown. Which of the suggested vectors could represent the impulse which I applied to the ball? Before After 1: 2: 3: 4: I = Δ p p f -p i I = p f –p i or p f = p i + I
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The Collider Detector at Fermilab (CDF) •CDF was designed to detect the debris from proton/anti- proton collisions •In 1995 we discovered the 2 nd to last piece of the standard model of particle physics (the top quark). •Momentum conservation played a large roll in the analysis My Ph.d experiment (along with 400 other Physicists from 30+ universities and 12+ Countries).
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Conservation of Momentum Alows us to “See” invisible particles ± Measure momentum from shape of track (high curvature implies low momentum) ± Momentum before collision is zero, so momentum after collision should also be zero ± Large amounts of “missing” momentum implies that a neutrino was created during the collision.
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Detailed 1d collision example 1 2 Before A ball with mass m 1 moves with v 1i . It strikes a second ball with mass m 2 . What are the final velocities? f f i v m v m v m 2 2 1 1 1 1 + = This is one equation with two unknowns: v 1f and v 2f . It has infinitely many solutions! 1 2 1 2 Either of these, and many others, would conserve momentum! After
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also need to know something about what happens to the energy of the system! We will consider several limiting cases… What if the balls stick together? v 1f = v 2f = v f ( ) () i f f i v m m m v v m m v m 2 1 1 2 1 1 1 + = + = 1 2 Before 1 2 After Limiting cases? m
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This note was uploaded on 04/04/2008 for the course PHYSICS 140 taught by Professor Evrard during the Fall '07 term at University of Michigan.

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p140w07_ct_13 - Racquetball Striking a Wall Copyright:...

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