p140w07_ct_19 - Racquetball Striking a Wall Copyright:...

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Physics 140: Winter 2007 Lecture #18 March 20, 2007 Dave Winn Racquetball Striking a Wall Copyright: Loren M. Winters Mt. Etna Andrew Davidhazy
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Tonights Homework Postponed • Due to a daylight savings time SNAFU it “looks” like tonights homework is due Wednesday. • It is really due at 1am Wednesday, which is basically tonight • I will change this so that it is really due Wednesday night • Next week we will go back to Tuesday at midnight due times.
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Equilibrium and motion around it • Most motion is not constant velocity or constant acceleration • Most common: little disturbances around equilibrium • Three forms: stable, neutral, and unstable
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Potential energy curves and equilibrium • Imagine a force which has a potential energy curve like that shown • The force everywhere is F = -dU/dx • Force is zero when slope of potential is zero U(x) x When the force is zero, the object can remain at rest. These are equilibrium points. Stable Unstable
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Potential minima and oscillations • Potential maxima are points of unstable equilibrium • Potential minima are points of stable equilibrium • If you move anything a little way from a stable point, it will oscillate back and forth Any small disturbance of an object at equilibrium leads to oscillations.
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Motion around stable equilibrium • At a stable point: forces always push back toward equilibrium • Restoring forces cause oscillations around equilibrium • Demonstrations of oscillations… • Two factors affect oscillations – Strength of the restoring force – Inertia of the object which is moving • The combination of these determines the frequency of oscillation Many oscillations we don’t see are fast or have small amplitudes. To make slow oscillations we need small restoring forces or large inertias…
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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_19 - Racquetball Striking a Wall Copyright:...

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