Vibrations and Waves now were shaking

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Vibrations and Waves(now were shaking!)

• Physics 1010
• November 13, 2007
• Dr. Don Franceschetti

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Hewitt really says this

• A vibration is a wiggle in time.
• A wave is a wiggle in both space and time.
• The source of any wave is something that is
  vibrating

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The Pendulum

• Is a mass hanging from a point of suspension on a
  string.
• Period is length of time between repetitions,
  depends on length but not on amplitude (if not
  too big) or mass. Can be used as a clock.
• Just as two falling bodies accelerate downward
  together (neglecting air resistance), Pendulums
  of different masses have the same period.
• Period determined by g/length. Used in
  exploration!

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Pendulum
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Ball and Spring

• Is a mass hanging from a spring.
• Period is length of time between repetitions,
  depends on mass but not on amplitude.
• Can be used as a clock also.

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Simple harmonic motion

• Is common to the pendulum, ball on spring, and
  projected uniform circular motion.
• Characterized by
• Amplitude how big a motion
• Period Time between repeat
• Frequency number of cycles per second (Hertz)
• phase

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Tracing Simple Harmonic Motion

• Ball on spring records path on moving paper

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Waves

• Any disturbance that travels through space
• Harmonic source generates harmonic wave
• Wavelength (l)
• Wave speed (v)
• Frequency (f)
• lf v

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Waves

• Longitudinal or Transverse

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Transverse waves only happen in solids (or
between different fluids).

• Since liquids and gases (fluids) flow when
  subjected to shear, only solids can sustain
  transverse waves in their interiors.
• Vibrating strings and plates and the surfaces of
  lakes can execute transverse vibration but sound
  in the air is longitudinal.

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Waves can be

• Transverse ocean waves, Seismic S waves
• Longitudinal sound waves, Seismic P waves
• Standing stringed instruments
• Traveling water wave

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Water Waves

• Are transverse

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Earthquake waves

• Can be shear (S) or pressure (P)

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Waves on a String

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Wave anatomy

• Crest, highest most positive part.
• Trough, lowest part.
• Node. In standing wave place where amplitude is
  zero.
• Antinode. In standing wave place where amplitude
  is maximum.

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Interference

• Waves passing through the same region of space
  add together at each point and time. (eps demos
  wave addition, ripple tank)
• Interference can also produce standing waves
  (eps demo, organ pipe)

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Doppler effect and the sound barrier

• A moving source will bunch wave creste on one
  side and draw them out on the other.
• When wave speed is exceeded, shock wave is
  produced
• Eps demo.

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Doppler Effect

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Leads to shock wave..

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Review questions.

• A grandfather clock keeps perfect time. Then it
  is brought to a summer home high in the
  mountains. Does it run faster, slower or the
  same? Explain.
• Why is lightening seen before thunder is heard
• How does the Doppler effect aid police in
  detecting speeding motorists?