Mach Cones and Beats

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Mach Cones and Beats
For next time Read Chapter 4, pp
1-3 Homework Chap 2 P12, P16, P25
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Moving source Doppler Effect
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Moving source Doppler Effect
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Moving source Doppler Effect
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Moving source Doppler Effect
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Moving source Doppler Effect
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Moving source Doppler Effect
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Moving source Doppler Effect
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Faster moving source
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Faster moving source
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Faster moving source
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Faster moving source
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Faster moving source
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Faster moving source
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Really fast moving source
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Really fast moving source
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Really fast moving source
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Really fast moving source
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Really fast moving source
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Really fast moving source
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vsound Dt
vsource Dt
Mach Cone
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You look directly overhead and see a plane
exactly 1 km above the ground traveling Mach 2.
How far will the plane travel before you hear the
sonic boom?
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You look directly overhead and see a plane
exactly 1 km above the ground traveling Mach 2.
How far will the plane travel before you hear the
sonic boom?
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?
1 km
q 300
x 1.7 km
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BEATS
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BEATS
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• results from interference of two slightly
  different frequencies

fbeat f2 - f1
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You are singing along with Celine Dion on the car
radio as she sings a long steady note. You know
that you are a little off key because you are
hearing beats at 2 hertz. Are you singing a
little too high, a little too low, or cant you
tell?
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• (Ch2, Prob. 14) A guitar string produces 4
  beats/second when played simultaneously with a
  250 Hz tuning fork AND 9 beats/second when played
  with the 255 Hz tuning fork. What is the actual
  frequency of the guitar string?

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• P 15 You are standing near two cars, A and B,
  which are both at rest. Each car has a siren
  that, when sounded together, produce beats at a
  frequency of 4 Hz. Car A now drives away and you
  hear the beat frequency increase.
• Will the frequency of the sound you hear from Car
  A be higher or lower compared to its rest value
  while it is driving away? Explain your
  reasoning.
• Which of the cars has the siren with the lower
  frequency? Explain your reasoning.