英语听力文摘 English Digest 484、漂浮的热气球（在线收听）

Why is it that you can’t put down hydrogen gas? If you had a big balloon full of hydrogen gas, like the first gondola balloons pioneered in 18th-century France, you’d find that it rises in the air quite dramatically.

You know that a piece of wood will float in water, right?

Sure.

That’s because the wood is less dense than the water. When you’re in a buoyant medium, having a lesser density than your surroundings means you’ll float. Something with greater density than water, like a stone, will sink.

Air also has the quality of buoyancy. Anything less dense than the air will rise, just like a piece of wood held underwater and then let go. Hydrogen gas is only about one fourteenth as dense as air. So up it goes!

In fact, it rises with such force that it can even haul up a huge balloon, with a gondola and riders!

为什么氢气总是会飘起来？如果你有一个充满氢气的大气球，就像18世纪法国飞行先去发明的吊篮热气球，你会发现热气球在空中飘得很高。

你知道一块木头能浮于水上，是吧？因为木头密度比水的密度小。当你所在的浮力介质密度小于周围，你就会飘起来。石头一类密度大于水的密度的就会下沉。

空气也有漂浮的特质。密度小于空气的就会漂浮，就像放在水下的木头会浮起来一样。

氢气的密度仅仅是空气密度的1/14，所以氢气能漂浮。而氢气上升的力量足以托起载客的吊篮热气球。