Waves

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Waves
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What is a Wave?

• A wave is an energy vibration that usually takes
  place in matter
• Key word vibration. Waves repeat
• A single wave is called a pulse

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Wave Types

• Transverse Waves vibrate at a right angle to
  their direction of motion
• Examples Light, ocean waves, waves on a rope

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• Longitudinal Waves vibrate in the direction of
  motion
• Examples Sound, P-Waves, Slinky Waves

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Wave Properties

• We use four different characteristics to talk
  about waves frequency, wavelength, amplitude,
  period, and speed
• Wavelength is the distance between identical
  parts of a wave (crest?crest, trough?trough)
• Amplitude is half the waves total height, or the
  distance between the crest and the rest position

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Wave Time

• A waves period is the time it takes for one
  vibration to occur
• If you divide wavelength by time, you get a
  waves speed (speed distance/time)

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Frequency

• A waves frequency tells us how often waves occur
  (2 waves a second, 4 waves a second, etc)
• The units of frequency are Hertz, or Hz
• 1 Hz 1 wave/second
• Frequency 1/period

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Source or Medium Dependence?

• Amplitude?
• Source Energy
• Period
• Source
• Speed
• Medium
• Wavelength
• Medium/Source

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Some Wavelengths

• Microwaves .03 m
• Radio Waves 10 m
• Ocean Waves 200 m
• Tsunami 11,000 m
• 200,000 m

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Two Views

• Position/Time View
• We focus on how one point on the wave evolves in
  time
• Snapshot View
• We focus on how the wave evolves in multiple
  dimension

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Time View
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• Which wave properties can we deduce from this
  graph?

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Snapshot
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• What can we deduce from this graph?

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Interference with Standing Waves
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Resonance

• Questions of Interest
• Can you break a wine glass with sound?
• Why did the Tacoma Narrows bridge collapse?

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Forced Vibrations

• Vibrating an object at a specific frequency
• Think back to the lab from last week (part C)
• Forced vibrations can create either organized or
  unorganized patterns
• On what does the patterns organization depend?

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Natural Frequency

• Most objects (media) have so called natural
  frequencies
• If we vibrate an object at one or more of its
  natural frequencies, something interesting occurs

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Resonance

• When a source vibrates an object at its natural
  frequency, we call it resonance
• You can create large amplitudes with fairly small
  input

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Other Examples?

• Swing sets
• Singing in the shower
• Tuning fork
• Standing waves on spring

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Raising the stakes

• If you continue vibrating something at its
  resonance frequency, the amplitude of the
  vibration increases

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Shattering a Wine Glass?
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