# why do helium balloons rise into the air?

what makes a balloon rise

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Helium balloons work by the same law of buoyancy. In this case, the helium balloon that you hold by a string is floating in a "pool" of air (when you stand underwater at the bottom of a swimming pool, you are standing in a "pool of water" maybe 10 feet deep -- when you stand in an open field you are standing at the bottom of a "pool of air" that is many miles deep). The helium balloon displaces an amount of air (just like the empty bottle displaces an amount of water). As long as the helium plus the balloon is lighter than the air it displaces, the balloon will float in the air.

It turns out that helium is a lot lighter than air. The difference is not as great as it is between water and air (a liter of water weighs about 1,000 grams, while a liter of air weighs about 1 gram), but it is significant. Helium weighs 0.1785 grams per liter. Nitrogen weighs 1.2506 grams per liter, and since nitrogen makes up about 80 percent of the air we breathe, 1.25 grams is a good approximation for the weight of a liter of air.

Therefore, if you were to fill a 1-liter soda bottle full of helium, the bottle would weigh about 1 gram less than the same bottle filled with air. That doesn't sound like much -- the bottle itself weighs more than a gram, so it won't float. However, in large volumes, the 1-gram-per-liter difference between air and helium can really add up. This explains why blimps and balloons are generally quite large -- they have to displace a lot of air to float.

• Anonymous

helium is light weight. lighter than "air". air near the surface of the planet is mostly Nitrogen and Oxygen and CO2 which all weigh more than 14 grams/mol. helium weighs 2 grams per mol. therefore it floats like a bubble in water to a place where the air around it is approximately the same weight.

the heavier gasses are closer to the earth than the lighter ones because gravity pulls them closer.