why does heluim make a ballon float upwards?

Question

daughter school project

Answer 1

helium is lighter then air and therefore the balloon rises

Answer 2

The reason the balloon rises is because the air at the bottom of the balloon is slightly more dense than the air at the top of the balloon. That means more molecules colliding with the bottom half of the balloon than with the top half. This creates an upward force call buoyancy which is determined by the displacement of the object (how big it is). The force is exactly the same as the buoyancy force on a cannonball of the same size. The reason the cannonball doesn't float is because the force of gravity (which is in opposition to the buoyant force) is much greater for the more massive cannonball. Because helium is so light, the sum of the mass of the balloon skin and the gas contained within the balloon does not create sufficient gravitational attraction to overcome the buoyant force. As the balloon rises, the difference in the density between the top half of the balloon and the bottom half decreases (as does the gravitational attraction, but only very slightly). At some point the buoyant force equals the gravitational force and the balloon's position will stabilize. Interestingly, in the absence of any wind or change in atmospheric pressure, the balloon will actually oscillate (go up and down) because the force differential will have to overcome the momentum of the balloon - sort of like a vertical pendulum.

Answer 3

Its the same reason why bubbles of air float upwards when in water.
The lighter air rises above the water for the same reason that water when immersed in air falls to the bottom of it.
In water the particles are closer together than in air (it is more dense) which means it feels the effect of gravity more, pushing the air upwards with a greater force than gravity is pulling the air downwards.
You have to remember that things stationary on the earths surface are bing pushed upwards by a force equal to that of gravity pulling them downwards. However, when these forces are unbalanced things begin to move (like when air is in water)
This is analogous to the helium ballon, but the helium is less dense than air and so it moves upwards instead.

Answer 4

Because helium is a gas, and gas is lighter than air.

Answer 5

its lighter than air