英语听力文摘547 气球不见之后发生了什么？

Fairs, carnivals, festivals or anywhere you can buy helium-filled balloons, you’re sure to see at least one balloon rising into the sky after someone accidentally lets it go off.

What happens to the balloon after it rises out of sight? well,that depends on how high the balloon goes!

When you inflate a balloon, you’re actually putting gases, mostly helium,in this case , into an elastic container. As you add more gas, the pressure inside the balloon increases, and in response, the balloon expands…up to a point, that is! If you put in too much helium, and the pressure inside the balloon gets too much higher than

the atmospheric pressure on the outside of the balloon, the balloon will burst.

So what happens to a rising balloon? Well, if it gets caught by an air current and is carried along level to the earth’s surface, it could go a long way,

even across the ocean,if the winds arrived! Of course, no balloon is perfectly sealed, no matter how tightly you tie it, so eventually the helium will leak out, and the balloon will sink.