英語(yǔ)聽力文摘636 地心引力為何對(duì)我們有好處
When astronauts return from long missions in space, their exit from the spacecraft is usually hidden from public view. This is because after several months in weightless conditions, things we usually take for granted, such as walking and keeping our balance, present great difficulties for the astronauts.
Forces Around Us
The culprit is gravity, or the virtual lack of it in space. Gravity is the force with which particles of matter attract each other. The greater its mass, the stronger an object’s gravitational force.
That’s why we normally stay rooted to the surface of the earth instead of floating off; the earth’s mass is much greater than ours.
Medical Problems
This gravitational state of affairs might seem rather limiting: wouldn’t it be fun to be able to float around like astronauts?
Perhaps, but anyone who spends an extended period of time in space faces serious medical problems due to the near total absence of gravity.
For instance, the small bones and fluid of the inner ear that allow us to keep our balance and know which way is up depend on gravity.
Weightlessness
In weightlessness, astronauts often initially experience intense dizziness, and are sometimes unable to orient themselves to their hands and feet. What’s worse, our bones, ligaments and muscles all maintain strength by working against the weight caused by gravity.
Without weight, bones weaken, ligaments deteriorate, and muscles atrophy. That’s why astronauts who have been in space for many months have trouble walking when they return to earth.
地心引力為何對(duì)我們有好處?
當(dāng)宇航員在太空長(zhǎng)時(shí)間執(zhí)行任務(wù)后返回地球的時(shí)候，他們走出太空飛船的場(chǎng)景往往不曝光于公眾。其間的原因便是：在失重的狀態(tài)下生活多個(gè)月以后，一些我們認(rèn)為理所當(dāng)然能夠做到的事情，如走路或保持平衡等，對(duì)宇航員來說卻相當(dāng)?shù)睦щy。
環(huán)繞四周的力量
這個(gè)罪魁禍?zhǔn)妆闶堑匦囊Γ蛘哒f太空缺地心引力。地心引力是指有質(zhì)量的物體間相互吸引的力量。一個(gè)物體質(zhì)量越大，其地心引力越大。
由于地球的質(zhì)量遠(yuǎn)大于我們，所以我們總是能夠站在地球表面而非漂浮在空中。
醫(yī)療問題
萬事都處于引力的狀態(tài)似乎限制多多：跟宇航員一樣能漂浮起來難道不是一件很有意思的事情嗎?
事實(shí)并非如此，由于缺乏引力，長(zhǎng)期在太空生活的人將面臨嚴(yán)重的醫(yī)療問題。
例如，處于耳朵內(nèi)部的小骨與液態(tài)流質(zhì)對(duì)保持身體平衡意義重大，它們的健康狀態(tài)取決于引力。
失重
在失重狀態(tài)下，宇航員常常最先經(jīng)歷強(qiáng)烈的眩暈，經(jīng)常無法控制他們的手腳。更糟糕的是，我們的骨頭，韌帶以及肌肉需要與引力產(chǎn)生的重量抗衡方能保持強(qiáng)健。
在失重的情況下，骨頭變得脆弱不堪，韌帶情況惡化，肌肉萎縮。這就是為什么宇航員在數(shù)月的太空工作返回地球之后，連走路都變得困難起來的原因。
