新概念英语听力mp3下载第四册lesson 40 Waves

 
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Waves are the children of the struggle between ocean and atmosphere, the ongoing signatures of infinity. Rays
from the sun excite and energize the atmosphere of the earth, awakening it to flow, to movement, to rhythm, to
life. The wind then speaks the message of the sun to the sea and the sea transmits it on through waves – and
ancient, exquisite, powerful message.
These ocean waves are among the earth’s most complicated natural phenomena. The basic features
include a crest ( the highest point of the wave), a trough (the lowest point), a height (the vertical distance from
the trough to the crest), a wave length (the horizontal distance between two wave crests), and a period(which is
the time it takes a wave crest to travel one wave length).
Although an ocean wave gives the impression of a wall of water moving in your direction, in actuality
waves move through the water leaving the water about where it was. If the water was moving with the wave,
the ocean and everything on it would be racing in to the shore with obviously catastrophic results.
An ocean wave passing through deep water causes a particle on the surface to move in a roughly circular
orbit, drawing the particle first towards the advancing wave, then up into the wave, then forward with it and
then – as the wave leaves the particles behind – back to its starting point again.
From both maturity to death, a wave is subject to the same laws as any other ‘living’ thing. For a time it
assumes a miraculous individuality that, in the end, is reabsorbed into the great ocean of life.
The undulating waves of the open sea are generated by three natural causes: wind, earth movements of
tremors, and the gravitational pull of the moon and the sun. Once waves have bean generated, gravity is the
force that drives them in a continual attempt to restore the ocean surface to a flat plain.