Why does a helium filled balloon float up when it is released?

Answer 1

The gas helium is less dense than the nitrogen-oxygen mix of atmospheric air. So a balloon filled to the same pressure (or even higher) will have a lower density than the air around it, which will displace it (flow under it), forcing it upward. The balloon will rise until the combined weight of the helium and the balloon are the same average weight (density) as the surrounding air. Long before it reaches that altitude, a normal balloon will begin to expand and will usually pop (at an altitude of a few hundred to a few thousand feet).
Helium molecules are lighter than most air molecules in the atmosphere (mostly nitrogen and oxygen) therefore they are prone to rise while heavier molecules move downward.

Answer 2

Helium is lighter (has less mass) per unit volume than air, on average, and so it experiences less of a gravitational attraction towards the Earth than the surrounding air, and so rises above it.

Answer 3

Well, since pure Oxygen is heavier than air, a balloon filled with Oxygen would sink because it has heavier content inside it...

Pure Oxygen has a density of 1.428 the heavier the air filled inside the denser the air meaning dense air does not rise. Therefore the balloon is bound to sink to the ground.

Answer 4

Helium is lighter than air. So helium balloon will float or rise up in air.

Answer 5

Because the helium is lighter then the sorrounding air
Because the balloon PLUS the gas in it weights less than the volume of air displaced by the balloon.

Answer 6

Simply because.... Helium is lighter than the surrounding air. The balloon will rise until the pressure of the gas inside breaks the rubber.

Answer 7

Because helium is lighter than air

Answer 8

Because helium is lighter than air.