AP1200_Ch3_Waves-2Principles-2007

AP1200_Ch3_Waves-2Principles-2007 - AP1200 3. Waves...

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1 AP1200 – 3. Waves Concepts AP1200 – 3. Waves Concepts 3.2 Wave principles 3.2 Wave principles Michel A. Van Hove Michel A. Van Hove WARNING: PRINTING THIS DOCUMENT WILL USE MUCH INK AND WILL NOT SHOW ANIMATIONS.
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2 Human waves in sports stadium Human waves in sports stadium “The wave” “La Ola” 8
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3 A human wave pulse: one person’s motion A human wave pulse: one person’s motion time Perform this up-down motion once : first all together to synchronize up-down speed then with normal reaction time between individuals observe speed of propagation along chain then with slower up-down speed, but same reaction time change in speed of propagation along chain? then with normal up-down speed, but 1 sec delay change in speed of propagation along chain? 7
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4 A human wave pulse A human wave pulse (1 sec delay) (1 sec delay) What or who is the source? Can anyone act as a source? Yes! Because everyone simply copies the neighbor’s motion This is Huygens’ Principle: in a wave any point acts as source for its continuation space 6
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5 period T L period P delay D delay D delay D delay D Wave pulse speed: v = L/D independent of period P! in this case D = T/4, so v = 4L/T Note: pulse viewed as fct of time has same shape as pulse viewed as fct of space delay D time space
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6 L half period T/2 wave pulse speed v = L/D independent of period T! in this case D = P/8, so v = 8L/T Note: pulse viewed as fct of time has same shape as pulse viewed as fct of space delay D delay D delay D delay D delay D half period T/2 time space Doubling period P :
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7 period T L time space period T delay D wave pulse speed v = L/D shorter delay gives higher speed Note: pulse viewed as fct of time has same shape as pulse viewed as fct of space here pulse has “sine” shape delay D delay D delay D delay D delay D delay D delay D delay D delay D Halving delay D :
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8 here pulse has “box” shape Note: pulse viewed as fct of time has same shape as pulse viewed as fct of space wave pulse speed is not changed Change of pulse shape : time space
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here pulse has “sawtooth” shape Note:
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This note was uploaded on 01/11/2011 for the course AP 1200 taught by Professor Michela.vanhove during the Spring '10 term at City University of Hong Kong.

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AP1200_Ch3_Waves-2Principles-2007 - AP1200 3. Waves...

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