NATURE OF SOUND

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NATURE OF SOUND
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Types Of Waves

• ELECTROMAGNETIC WAVES
• require no medium in which to transfer energy.
  These waves are both electric and magnetic in
  nature, therefore we cannot directly view them
• X-rays, radio waves, light waves etc

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Types Of Waves

• MECHANICAL WAVES-
• require a medium (air, water, earth, etc..)
  through which they can travel

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TRANSVERSE WAVES

• TRANSVERSE WAVES
• vibration of the particles of the medium is
  perpendicular to the direction of the wave

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LONGITUDINAL WAVES

• LONGITUDINAL WAVES
• vibration of the particles of the medium is
  parallel to the direction of the wave
• Sound wave(caused by vibrating objects, which
  move back and forth)

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LONGITUDINAL SOUND WAVES
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LONGITUDINAL SOUND WAVES
The distance between adjacent condensations is
equal to the wavelength of the sound wave.
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LONGITUDINAL SOUND WAVES
Individual air molecules are not carried along
with the wave.
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THE FREQUENCY OF A SOUND WAVE
The frequency is the number of cycles per
second. A sound with a single frequency is
called a pure tone. The brain interprets the
frequency in terms of the subjective quality
called pitch.
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THE PRESSURE AMPLITUDE OF A SOUND WAVE
Loudness is an attribute of a sound that depends
primarily on the pressure amplitude of the wave.
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Sound travels through gases, liquids, and solids
at considerably different speeds.
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Lightning, Thunder, and a Rule of Thumb There is
a rule of thumb for estimating how far away a
thunderstorm is. After you see a flash of
lighting, count off the seconds until the thunder
is heard. Divide the number of seconds by five.
The result gives the approximate distance (in
miles) to the thunderstorm. Why does this rule
work?
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LIQUIDS
SOLID BARS
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Doppler Effect

• Named for its discoverer Christian Doppler
• Causes a change in observed frequency (pitch) of
  the waves when a wave source or observer is
  moving in relative motion
• Wavelengths in front of moving object are shorter
  than behind the object

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The Doppler effect is the change in frequency or
pitch of the sound detected by an observer
because the sound source and the observer
have different velocities with respect to the
medium of sound propagation.
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STATIONARY SOUND SOURCE
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MOVING SOURCE lt vsound
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MOVING SOURCE vSoundMach 1
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MOVING SOURCE gt vSound
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MOVING OBSERVER
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GENERAL CASE
Numerator plus sign applies when observer moves
towards the source
Denominator minus sign applies when source
moves towards the observer
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ULTRASOUND
By scanning ultrasonic waves across the body and
detecting the echoes from various locations, it
is possible to obtain an image.
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CAVITRON ULTRASONIC SURGICAL ASPIRATOR
Ultrasonic sound waves cause the tip of the probe
to vibrate at 23 kHz and shatter sections of the
tumor that it touches.
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DOPPLER BLOOD FLOW METER
When the sound is reflected from the red blood
cells, its frequency is changed in a kind of
Doppler effect because the cells are moving.
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END