听力文摘：漂浮的热气球

Why is it that you can't put down hydrogen gas? If you had a big balloon full of hydrogen gas, like the first gondola¹ 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 dense² than the water. When you're in a buoyant medium, having a lesser³ density⁴ 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。

1 gondola   

n.威尼斯的平底轻舟；飞船的吊船

参考例句：

• The road is too narrow to allow the passage of gondola.这条街太窄大型货车不能通过。
• I have a gondola here.我开来了一条平底船。

2 dense   

a.密集的，稠密的，浓密的；密度大的

参考例句：

• The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
• The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。

3 lesser   

adj.次要的，较小的；adv.较小地，较少地

参考例句：

• Kept some of the lesser players out.不让那些次要的球员参加联赛。
• She has also been affected,but to a lesser degree.她也受到波及，但程度较轻。

4 density   

n.密集，密度，浓度

参考例句：

• The population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
• The region has a very high population density.该地区的人口密度很高。