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one of the Universal Laws of Gravitation ::
the gravitational force on an object increases as mass increases

helium has mass
how come when you add more and more of it, it flaots higher? shouldn't it get lower ( you know what i mean)... i never really realized this but i has a science test today and was like wait a second!!!
-edit-
I know helium is lighter than air, does that have anything to do with it? it still has mass though? help please..

2006-10-20 10:17:12 · 7 answers · asked by Psychedelic Worm 3 in Science & Mathematics Physics

7 answers

This is basically buoyancy in action:

Buoyancy works to make things seem lighter than they are because to push something into a fluid, you have to displace some of the fluid to do it. The fluid wants to get back in, so it's essentially trying to force the object out again. The amount of force this applies depends on the volume of the object, and the density of the fluid.

For example, if you push a two-liter bottle under water, there's two liters of water you're going to be pushing out of the way. Those two liters of water typically weigh about two kilograms, or roughly five pounds, so you'll feel five pounds of pressure pushing back up. OR whatever's in the bottle seems to weigh five pounds less...

This also explains why boats can float (their weight is much less than the water they displace) and how changing the volume of something can make it float or sink (like if you hold a lot of air in your lungs instead of making them empty).

This works in the atmosphere too. By walking around on the ground, you're displacing some air that wants to be where you are. Air is a lot less dense than water, but it still provides you with a little buoyancy, if only a few grams' worth. But this is enough to make helium and hot-air balloon float!

2006-10-20 10:33:21 · answer #1 · answered by Doctor Why 7 · 1 0

basically a helium balloon floats in the air.

the same way an air bubble floats in water (goes up). the same way an air-filled balloon, in water, wants to go up to get to the surface.

you'll probably agree that, the more air you put in a balloon, the stronger it will put upwards, if immerged in water, right?

same happens with a helium balloon in air

you may know, Archimedes was the first to find it out, that the buoyancy force on an object, is equivalent to the weight of the volume of the milieu, displaced by the object.

if, say, you double the volume of your helium balloon, it displaces twice as much air, and so gets a twice bigger buoyancy force, which is much larger than the weight of helium + balloon.


this being said, it would be more proper to say, "it pulls up stronger". Because when you go higher and higher, there are other effects to take into account, and the optimal solution is to fill the ballon just enough so that it will take off.

2006-10-20 12:35:38 · answer #2 · answered by AntoineBachmann 5 · 0 0

It's true, helium has mass, and gravity pulls on any mass with a force equal to its mass times a constant (9.8 N/kg). The issue is that a volume of air equivalent in size to the balloon will have more mass than the balloon, thus gravity will pull on it with greater force, and develop a greater pressure. Since any given volume can either be occupied by air or by the balloon, it makes sense that if the air and the balloon are free to move, then the volume with greater force on it will move toward the force of gravity. The force on that volume will cause a pressure in the volume of that fluid which is proportional to its density, and that pressure will "displace" the lighter object since the fluid pressure will push it upward.

2006-10-23 21:51:23 · answer #3 · answered by Mike 2 · 0 0

What you have to consider is the "Weight" of the material the balloon is made of and the "Weight" of the amount of Helium in the balloon vs their "Total Displacement" vs the "Weight" (density) of the the air around it.

You will find that the More Helium you add to a Balloon (without making it expand to a point where you have exceeded it's tensile strength and it bursts) the higher it will go in the atmosphere, because it's density is less than that of air at that particular altitude. When your Balloon gets to an altitude where it's density matches the surrounding air density it will "float" there.

This is not much different than throwing a brick in the ocean where the ocean is VERY DEEP. If the Brick has many tiny trapped air bubbles then there is a chance for it to get to a certain depth and "Float" there without ever going to the sea floor becuase it's density is the same as the water at that depth. ;-)

2006-10-20 10:31:51 · answer #4 · answered by TommyTrouble 4 · 0 1

Since helium has a smaller molecular weight than the gaseous mixture of air, it is less dense. Therfore regardless of much helium you use, or how "heavy" it is, it will orient itself above the denser air.

Its the same reason why wood floats a brick of wood floats on water, and a brick of steal sinks.

2006-10-20 10:26:40 · answer #5 · answered by M 2 · 0 0

Because a larger volume of lighter (less dense) helium displaces a larger volume of heavier (more dense) air. Ergo it goes higher (to within a limit).

2006-10-20 12:44:07 · answer #6 · answered by delujuis 5 · 0 0

the air that the balloon displaces exerts greater pressure than the weight of the additional helium.Sort of like the Archimedes pricipal.A object wholly or partially emerged in a liquid is buoyed up by a force equal to the weight of the liquid displaced

2006-10-20 10:22:19 · answer #7 · answered by Paul I 4 · 0 1

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