Chapter 12.1-SOUND

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Chapter 12.1-SOUND
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4. SPEED OF SOUND

• Much slower than light
• Thunder and Lightning
• Five second delay per mile
• Depends on wind, temperature, humidity

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Speed of Sound
The Speed of Sound depends on the density of the
medium through which the sound waves travel.
Medium In ft./s In m/s
Air at 20 C 1116 340
Distilled Water 25 C 4908 1496
Seawater 25 C 5023 1531
Steel 17100 5200
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Reflection
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Loudness is related to the energy (amplitude) in
the sound wave. The pitch of a sound refers to
whether it is high, like a flute, or low like
string bass. The lower the frequency of sound,
the lower the pitch.
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ENERGY IN SOUND WAVES

• Energy in sound is weak when compared to the
  energy in light.
• The human ear is a remarkable detector.
• 10 million people speaking at the same time
  produce approximately enough energy to light one
  flashlight.

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Loudness Intensitymeasured in decibels
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Pitch

• Relative highness or lowness of a note.
• adding PITCH to rhythm and amplitude creates
  melody

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Frequency

• A sound that vibrates back and forth 1,000 times
  per second like a tuning fork has a frequency of
  a 1,000 Hz
• The frequency of the human auditory system has a
  range from 20 Hz to 20,000 Hz

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• Frequencies for
• musical notes

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Octave

• a pitch an octave higher than another has ii20
  double its frequency
• Example 440 Hertz 2 880 Hertz
• a pitch an octave lower has ii21 half the
  frequency
• Example 440 Hertz .5 220 Hertz

A3 A4 A5
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Standing waves in instruments

• Guitar all stringed instruments have sounding
  boards or boxes to amplify sound!
• (hyperlink on picture)

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Ultrasonic Sound

• Anything above frequencies, anything above 20,000
  Hz
• Used for communication and navigation by bats and
  dolphins

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Ultrasonic Waves

• Ultrasonic waves are short
• Widespread medical applications
• Used to produce images inside the human body
• hyperlinks on each image

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Infrasonic Waves

• Sound waves with frequencies less than 20 Hz.
• They are produced by such things as heavy
  machinery and thunder.
• They are really low pitched sounds.
• Elephants can communicate from kilometers away
  using infrasonic waves.

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Elephants hear through their feet.

• Flexible, soft skin of the foot acts like a drum
  head, which sense vibrations which travel from
  the toe nails to the ear by bone conduction.
  Foot stomping and low frequency rumbling
  generated by one group of elephants are picked up
  by another group far away.

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FORCED VIBRATIONS

• Demo - Tuning Fork Touching a Table
• Sound is intensified because of the larger
  surface area that can vibrate the air.
• The surface is forced to vibrate at the frequency
  of the tuning fork. (It is not a resonance
  phenomenon.)
• Examples Musical sounding boards

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NATURAL FREQUENCY

• Demo - Drop Different Sounding Objects
• Objects have natural frequencies at which they
  vibrate.
• The natural frequency depends on elasticity and
  shape.

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RESONANCE

• Resonance occurs when we force a vibration at the
  
• same frequency in
• another object.

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Middle Ear Schematic
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