英语听力文摘 English Digest 176、大气层摩擦热

　　Reentry Heat
[Why does a space shuttle get hotter on reentry than on liftoff?]
能想象航天飞机穿越大气层时受到摩擦产生的热量有多惊人吗？来一起听听吧。
M:Dolle,we now know that the space shuttle Columbia burned up when it reentered Earth’s atmosphere because its thermal¹ insulation² was damaged. But, if the insulation was damaged during take-off, why didn’t the shuttle burn up on the way out of the atmosphere?
W:Well done.The space shuttle does get hot when it leaves the atmosphere, but not nearly as hot as when it comes back.
M:Why not?
W:Friction³ between the shuttle and the atmosphere makes for high temperatures. But two factors determine just how much friction there is: the speed of the shuttle and the thickness of the air.

　　M:I know the air is thickest near sea level because there are more air molecules⁴ there.
W:That's right.So when the shuttle takes off, it hits a lot of air molecules at first, which causes friction. But, the shuttle is still going pretty slowly, so the friction is not too great, and the shuttle doesn’t get very hot.
By the time it gets to full speed, it’s just about out of the atmosphere.
M: And there are fewer air molecules to make friction up there.
W:Right.Now on the way back down, the situation is reversed. The shuttle starts off at full speed, and it actually uses the friction from air molecules like brakes to slow it down. So the shuttle goes through the thickest parts of the atmosphere very, very fast–much faster than when it took off.The friction from reentry can cause the shuttle to reach temperatures greater than two-thousand degrees Fahrenheit⁵.
M:This can be dangerous for the shuttle and its crew, as we learned when the Columbia was lost.

1 thermal   

adj.热的，由热造成的；保暖的

参考例句：

• They will build another thermal power station.他们要另外建一座热能发电站。
• Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。

2 insulation   

n.隔离；绝缘；隔热

参考例句：

• Please examine the insulation of the electric wires in my house.请检查一下我屋子里电线的绝缘情况。
• It is always difficult to assure good insulation between the electric leads.要保证两个电触头之间有良好的绝缘总是很困难的。

3 friction   

n.摩擦，摩擦力

参考例句：

• When Joan returned to work,the friction between them increased.琼回来工作后，他们之间的摩擦加剧了。
• Friction acts on moving bodies and brings them to a stop.摩擦力作用于运动着的物体，并使其停止。

4 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

5 Fahrenheit   

n./adj.华氏温度；华氏温度计(的)

参考例句：

• He was asked for the boiling point of water in Fahrenheit.他被问到水的沸点是华氏多少度。
• The thermometer reads 80 degrees Fahrenheit.寒暑表指出华氏80度。