英语听力文摘 English Digest 420、无形的力量（在线收听）

The Invisible Hand

无形的力量

A: What's going on?

B: Check out the setup , Yaoyao.

A: A stove, an empty aluminum soda can, kitchen tongs, and a saucepan. Are you experimenting with a new recipe?

B:No,  i'm experimenting with air pressure.

A:How?

B:First, i will put about a tablespoon of water in the soda can, and a little cold water in the saucepan. Now, I will heat the water in the soda can on the stove until it boils.

A: There steam coming out of the can.

B: Good! Now watch, i will pick up the can with a kitchen tongs like this and put it face down in the cold water in the pan. Ready?

A:Ready!

B:Here goes!

A: Wow, the can collapse like with being crushed down by an invisible hand.

B: When the water in the can boiled, the water vapor pushed all the air out of the can. And when I flipped the can and put it in the pan, the cold water cooled the vapor, making it condense. 

A:Which left the can empty inside, allowing the pressure of the air outside the can to crush it.

B: Exactly. Normal air pressure is about 15 pounds per square inch. Since the can was about three inches high and two inches wide, the air pressure on it was 15 pounds per six inches, or ninety pounds of air pressure used to crush the can.

A: Very interesting!

A:发生什么事了？
B:瑶瑶，看一下都有些什么设备吧！
A:火炉，铝制的的易拉罐，餐钳和平底锅。你是在做一个新的食谱吗？
B:不是的，我是在做一个关于气压的实验。
A:怎么做？
B:我先在易拉罐里加入约一汤匙的水，在平底锅里加少许冷水。接着，将易拉罐放在火炉上加热至其沸腾。
A:这样水蒸汽就从罐子里冒出来了。
B:对了！现在，我要用餐钳像这样将易拉罐夹起来，并将其正面放在有冷水的平底锅里。准备好了吗？
A:准备好了！
B:看看会发生什么吧！
A:哇噢，易拉罐碎了！就像被一只无形的手给压碎的！
B:因为在（易拉罐里的）水沸腾时，罐子里的所有空气都被水蒸汽排出。所以当我将罐子翻转过来放在平底锅里时，（锅里的）冷水将水蒸汽冷却、凝结。
A：这就使得易拉罐内部变空，从而让外面的气压将其粉碎。
B：非常正确！正常的气压大约是每平方英寸15磅。由于易拉罐大约是3英寸高、2英寸宽，它周围的气压就是6平方英寸15磅，即每平方英寸90磅，从而将易拉罐粉碎。
A:太有意思了！