Sound Ch. 26.1-26.3

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SoundCh. 26.1-26.3
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Review

• Whats a wave? What does it transport?
• Wave is a disturbance traveling through a medium
  transporting energy from one location to another.
• Remember the slinky? How is its wave similar to
  sound waves? Any guesses?

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Listen . . .

• Listen, quietly, for a few minutes, writing down
  the name of each sound you hear, and where it is
  coming from
• Sound is the only thing that our ears can hear.
  The source of sound or any wave motion is a
  vibrating object

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Quick Demo

• Strike the prongs of a tuning fork with a pencil
  and then hold the fork close to your ear.  What
  happens?  Touch the prongs of the fork.  What
  happens?
• Strike the prongs of the tuning fork and place
  the ends of the prongs in a glass of water.  What
  happens?

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Objectives

• Relate the pitch of sound to its frequency
• Describe the movement of sound through air
• Describe how bats and dolphins use sound
• Compare the transmission of sound through air
  with that through solids, liquids, and a vacuum

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Origin of Sound

• All sound produced by vibrating source
• Strings on a guitar --gt sound board (demo?)
• Reed in a saxophone --gtair column in sax

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Quick Physiology Lesson

• Creating Sound
• Put your hand on your throat when you talk
• Windpipe blows air across your chords in your
  throat causing them to vibrate and make a sound
• Rubber band and cup demo
• Listening . . .

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Determining Pitch

• Lets review frequency. What is it?
• Frequency of vibrations per second Hz)
• Pitch of a note determined by frequency
• High frequency --gt high pitch

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Pitch of Wind Instrument

• Wind instruments have a long, thin column of air
• Sound wave travels down tube, reflects off of the
  top and bottom, until it can escape
• Longer the tube, lower the f, lower the pitch
• Shorter the tube, higher the f, higher the pitch
• Opening/closing holes changes tube length which
  changes pitch
• Demo with recorder

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Remember

• Sound waves are mechanical waves
• require a medium in order to transport their
  energy
• Whats the medium used to get this sound to your
  ears?

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What pitches can we hear?

• 20 to 20,000 Hz
• Sound waves
• below 20Hz
• Infrasonic
• above 20,000Hz
• Ultrasonic

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Elephants and Bats
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Dolphins

• Send sound to the sea floor --gt creates image
• Send sound to other dolphin --gt put image in
  their head
• Receive and send info with the same sense.
• Do humans?

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Checkpoint

• The higher the frequency of a wave, the _________
  the pitch.
• higher
• Which chamber in a trumpet would produce a lower
  frequency a short chamber or a long chamber?
  Why?
• Longer chamber --gt longer wavelength --gt lower
  frequency

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Compressed Air

• Vibrations produce pulses of compressed air,
  remember?
• Do sound waves move like the slinky or the
  spring? (show both) What type of waves are
  sound waves?
• Longitudinal!

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Compressions vs. Rarefactions

• These pulses push into their neighbors, who push
  their neighbors, etc.
• Compressions
• pulse of compressed air
• i.e., door/curtain
• Rarefaction
• a disturbance in air when pressure is lowered
• Candle Demo

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Sound needs a medium
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What are the best conductors of sound?

• Put these in order liquid, air, solid.
• Why is one a better conductor than the other?
• Depends on objects elasticity--more on this next
  lecture
• Can you hear voices in outer space?
• Tin can activity