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Wave Mechanics → Two Classes of Waves
The Two Classes of Waves
All waves in nature - sound waves, radio waves, any waves - can be classified as one of two
types. All waves are either transverse
or longitudinal.
Transverse Waves
Consider waves in water. The waves travel horizontally
through the water, and finally crash on the shore. But the water itself does not
travel in this way. Rather, each 'piece' of water; each water molecule; simply
moves up and down again as the wave moves past. The wave itself consists of nothing but these up
and down motions of individual particles, 'synchronised' to look like a wave
traveling toward the shore on a grand scale.
A transverse wave is simply
any wave in which the direction of motion of the particles (or the direction in
which the wave oscillates), e.g. vertically up and down in the case of water, is
at right angles to the direction in which the whole wave travels ('propagates').
In the case of water, the waves propagate horizontally towards the
shore.
Longitudinal Waves
What about sound waves? These are caused by air
vibrations which oscillate back and forth parallel to the direction in which the sound
wave travels. Such waves are said to be longitudinal. There is no preferred 'up'
or 'down' direction for an air particle to move, only backwards and forwards. A
speaker cone oscillates in and out to produce the vibrations, and your ear-drum
oscillates in and out in response to them.
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