英語聽力文摘484 漂浮的熱氣球

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!

為什么氫氣總是會飄起來?如果你有一個充滿氫氣的大氣球，就像18世紀法國飛行先去發(fā)明的吊籃熱氣球，你會發(fā)現(xiàn)熱氣球在空中飄得很高。

你知道一塊木頭能浮于水上，是吧?因為木頭密度比水的密度小。當(dāng)你所在的浮力介質(zhì)密度小于周圍，你就會飄起來。石頭一類密度大于水的密度的就會下沉。

空氣也有漂浮的特質(zhì)。密度小于空氣的就會漂浮，就像放在水下的木頭會浮起來一樣。

氫氣的密度僅僅是空氣密度的1/14，所以氫氣能漂浮。而氫氣上升的力量足以托起載客的吊籃熱氣球。