听力文摘：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.

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。

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

你知道一块木头能浮于水上，是吧？

Sure.

当然。

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.

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。

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!

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。

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

事实上，氢气上升的力量足以托起载客的吊篮热气球。