# Underwater Acoustics

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My Communications coursework will be on non-radio communications. My

chosen topic is underwater acoustics. The applications of underwater

acoustics and their advantages and disadvantages will be studied.

All forms of non-radio communications are based on waves. Waves are

generally a disturbance in a surface, transferring energy from A to B.

Waves can be mechanical vibrations travel through a medium. For

example: water, sound. These waves are called mechanical waves.

Progressive waves are created from a point and energy is distributed

to the surroundings. For example: dropping a pebble in the middle of a

pond causes energy to be distributed outwards. All waves can be

classed into two categories:

* Transverse waves: In Transverse waves the direction of the

particle movement is perpendicular to the direction of the wave.

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* Longitudinal waves: The particles in longitudinal waves travel in

the same direction as the direction of the wave.

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[IMAGE][IMAGE]Waves that can travel underwater without getting too

distorted are used for comunicating underwater. Sound waves fill this

criteria as they can travel long distances without getting distored

too much. Sound waves are longitudnal and mechanical waves. They are

longitudinal because when they travel they create an area of

compression and then rarefractions within the air. A sound wave, like

any other wave is introduced into a medium by a vibrating object. The

motion of the particles in the medium in which a sound wave vibrates

back and forth is measured by the frequency. The frequency of a wave

is measured as the number of complete back-and-forth vibrations of a

particle of the medium per second. Unit of frequency is Hertz (Hz).

The frequency of a wave can be altered by increasing the number of

vibrations per second. [IMAGE]Increasing the frequency, increases the

pitch of the wave. Any sound that can heard by a human ear is called

an infrasound (20Hz to 20000Hz). Above this range the sound is known