phys124s11-l06

phys124s11-l06 - Physics 124 Spring 2009 Physics 124, 25...

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1 Physics 124 Spring 2009 Physics 124, 25 February 2011 Spring 2010 1 st Exam Results: average ~ 55%, rms~13% Spring 2010 1 st Exam Results: average ~ 59%, rms~15% Average of good problems: 59% Average of problem problems: 59% Difference on repeated problems: +0.03% Easy: water speed in expanding pipe, pulley , water pressure, inclined plane, Schwarzchild radius , . .. Hard: Energy of earth satellite, water on mercury, Saturn mass from Titan orbit, floating block , orbit speed about Deimos,. .. Exam Results To err is human, to really foul up requires a computer −− various attributions
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2 Physics 124 Spring 2009 Physics 124, 25 February 2011 Lecture 5 Summary Many situations in which we have small oscillations / SHM mass on spring, pendulum, torsional pendulum, etc. Potential energy U x : for spring: with 2 = g l simple pendulum , mgd I pendulum , k m mass on spring , ... E = T U = 1 2 mv 2 1 2 kx 2 = 1 2 kA 2 Frequency f in Hz: f = 1 / T , so  = 2 f Period T : time until motion repeats: T = 2 , so T = 2 d 2 x dt 2  2 x = 0  x = Acos  t  F =− kx 
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3 Physics 124 Spring 2009 Physics 124, 25 February 2011 Today: One dimensional traveling waves in time x generally described by f x,t   f x vt for waves moving to +x x vt = constant more +x at later time For a wave of constant shape, moving with time: y successive snapshots pulse or sinusoid
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4 Physics 124 Spring 2009 Physics 124, 25 February 2011 Today: one dimensional traveling waves Needs: medium for mechanical waves not for light Interactions within medium that allow wave to propagate Source of energy and momentum to generate the waves Typically: wave speed is a property of the medium Wave shape depends on source: pulse vs. sinusoidal wave, frequency, amplitude But beware of large energy sources, like nuclear bombs, Oscillation / vibration / pulse energy that moves in some medium Energy moves, matter does not goes back where it started where large energy density changes the medium
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5 Physics 124 Spring 2009 Physics 124, 25 February 2011 Today: one dimensional traveling waves Needs: medium for mechanical waves not for light Oscillation / vibration / pulse energy that moves in some medium Energy moves, matter does not goes back to where it started
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6 Physics 124 Spring 2009 Physics 124, 25 February 2011 Longitudinal vs. Transverse Waves longitudinal waves: sound transverse waves: string, light and wavelength waves can be periodic or non periodic Demos. .. Both Land T waves: ocean waves, earthquakes
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phys124s11-l06 - Physics 124 Spring 2009 Physics 124, 25...

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