40 Waves

名称：40 Waves
内容简介：
新概念英语第四册（英音）
[al:新概念英语（四）]
[ar:MP3 同步字幕版（英音）]
[ti:Waves]

[00:01.54]Lesson 40
[00:03.21]Waves
[00:10.91]What false impression does an ocean wave convey to the observer?
[00:17.55]Waves are the children of the struggle between ocean and atmosphere, the ongoing signatures of infinity.
[00:26.32]Rays from the sun excite and energize the atmosphere of the earth, awakening it to flow, to movement, to rhythm, to life.
[00:36.58]The wind then speaks the message of the sun to the sea
[00:40.58]and the sea transmits it on through waves--an ancient, exquisite powerful message.
[00:48.64]These ocean waves are among the earth's most complicated natural phenomena.
[00:54.50]The basic features include a crest (the highest point of the wave),
[00:59.77]a trough (the lowest point), a height (the vertical distance from the trough to the crest),
[01:07.89]a wave length (the horizontal distance between two wave crests),
[01:13.45]and a period (which is the time it takes awave crest to travel one wave length).
[01:19.92]Although an ocean wave give the impression of a wall of water moving in your direction,
[01:25.99]in actuality waves move through the water leaving the water about where it was.
[01:32.43]If the water was moving with the wave,
[01:35.08]the ocean and everything on it would be racing in to the shore with obviously catastrophic results.
[01:42.76]An ocean wave passing through deep water causes a particle on the surface to move in a roughly circular orbit,
[01:51.32]drawing the particle first towards the advancing wave, then up into the wave,
[01:57.22]then forward with it and then--as the wave leaves the particles behind--back to its starting point again.
[02:05.22]From both maturity to death, a wave is subject to the same laws as any other 'living' thing.
[02:13.11]For a time it assumes a miraculous individuality that, in the end, is reabsorbed into the great ocean of life.
[02:22.79]The undulating waves of the open sea are generated by three natural causes:
[02:28.83]wind, earth movements or tremors, and the gravitational pull of the moon and the sun.
[02:37.07]Once waves have been generated,
[02:39.21]gravity is the force that drives them in a continual attempt to restore the ocean surface to a flat plain.