```Speed of Sound                                         Pitch
It depends on the medium the waves pass                   It is the sensation of a frequency of a
through, and is a fundamental property of the              sound wave.
material.                                                 A high pitch sound corresponds to a high
frequency sound wave and a low pitch
Material           Speed of Sound                  sound corresponds to a low frequency
Air at 200 C       343 m/s                         sound wave.
Air at 400 C       355 m/s
Water              1493 m/s                    Shock Wave
Sea Water          1533 m/s
Iron               5130 m/s
Rubber             1600 m/s                       It is a thin transitive area propagating with
supersonic speed in which there is a sharp
increase of density, pressure and speeds of
Perception of Sound
substance.
   It arises at explosions, detonation,
   The perception of sound in any organism                supersonic movements of bodies, powerful
is limited to a certain range of frequencies.          electric discharges etc. (1 Hertz = 1
   It can calculate with hertz (Hz).                      vibration/second)
   For humans, hearing is normally limited to
frequencies between about 20 Hz and                Echo
20,000 Hz (20 kHz).
   Dogs can perceive vibrations higher than
   It is the sound you hear when you make a
20 kHz, but are deaf to anything below 40
noise and the sound wave reflects off a
Hz.
distant object.
   In other words it is the refection sound.
Intensity (I)
   Sound travels 34 m in 0.1 seconds, so you
only hear echoes from surfaces that are at
   It is the power transferred per unit area.             least 17 m away.
   Its units is watt per metre squared (W/m2).           A person can typically hear his or her own
   It is used most frequently with waves (e.g.            echo where a hard surface, such as the side
sound or light), in which case the average             of cliff, reflects sound waves directly back
power transfer over one period of the                  to the person. The use of echoes to locate
wave is used.                                          objects is called echolocation.
   The intensity is the product of the sound             Reverberation is the collection of
pressure and the particle velocity, I  pv             reflected sounds from the surfaces in an
(Notice that both v and I are vectors,                 enclosure like an auditorium.
which means that both have a direction as
well as a magnitude.)                              SONAR
   The decibel (dB) is the unit used to
measure the intensity of a sound.                  Sonar (SOund Navigation And Ranging) is a
technique that uses sound propagation (usually
   Near total silence - 0 dB                          underwater, as in submarine navigation) to
   A whisper - 15 dB                                  navigate, communicate with or detect objects
   Normal conversation - 60 dB                        on or under the surface of the water, such as
   A lawnmower - 90 dB                                other vessels.
   A car horn - 110 dB
   A rock concert or a jet engine - 120 dB
   A gunshot or firecracker - 140 dB
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