# Helium lifting ability

Anyone know offhand without going to too much trouble, what is the ratio for volume of helium to lbs force against gravity ?
Fred
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A cubic foot of air at sea level under standard conditions weighs about 0.077 lb, so if you displaced that cubic foot of air with helium, the net lifting force would be slightly less than that (i.e., 0.077 lb minus the weight of a cubic foot of helium, which I don't know the value of offhand). Of course, you also have to subtract the weight of the container.
Bert

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Sounds like another budding lawn chair pilot in the making.
I'm not sure but the simple way would be to get a 4oz fishing weight and see how many balloons you need to lift it and multiply this by 4.
Saturday mornings at auto dealerships they usually have a whole lot of balloons they might let you play with.
-- Roger Shoaf If you are not part of the solution, you are not dissolved in the solvent.

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I believe a cubic foot of helium will lift about 28.2 grams. Multiply the volume times 28 and divide by 448 g/lb.
A 10' diameter weather balloon will lift about 32 pounds.
ff wrote:

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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helium lift cubic foot
...found more than one thousand, three hundred web pages with the information you want. No trouble at all.
-- --Pete
http://www.msen.com/~pwmeek /
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All bodies floating on or submerged in a fluid are buoyed up by a force exactly equal to the weight of the fluid they displace.
1 cubic foot of air= 0.0807 pounds at 32 F and 1 atm.
1 cubic foot of helium= 0.0111 (same conditions)
If you are planning a trip in a lawn chair that should provide the needed information.
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And -- of course -- one cubic foot of vacuum would lift the full 0.0807 pounds (again at STP), but the trick is finding a rigid container which doesn't weigh more than the lift. :-)

Be sure to file your flight plan. :-)
Enjoy,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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I thought that MAYBE I actually still had the paper those guys wrote--but no. Memory sez they did an aluminum geodetic frame covered with sheet aluminum triangles, all sealed with wax. I don't remember what stopped them--the sheets or the frame collapsing, or all the joints leaking.
David
"DoN. Nichols" wrote:

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wrote:

If the sides are not rigid it's always *exactly* atmospheric pressure. If it expands either atmospheric pressure has dropped or the temperature of the balloon has gone up.
Here's a question for everyone. Explain *exactly* the mechanics of how and why a balloon floats :^)? Not as easy as one might think.
And a second one is why when you have a helium balloon in your car and put the brakes on to stop, the balloon will float to the back of the car instead of flying to the front like everything else. Again, what are the mechanics that make it do so?
John
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gets
pretty
As I understand the physics, air is a fluid and the helium balloon being lighter than the air around it floats just as a drop of oil will float if released from the bottom of a volume of water.
Not as easy as one might think.

Again the air being heaver than the balloon the air has more mass. When this mass is in motion, pressure is equal on all sides of the balloon. When the brakes are applied the air inside the car keeps moving at the speed the car was going until it hits the windshield. As air bunches up in the front part of the car, there is more air pressure at the front of the car and less at the back so the pressure in the front pushes the lighter balloon backwards.
-- Roger Shoaf If you are not part of the solution, you are not dissolved in the solvent.
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On Sun, 20 Jul 2003 22:58:47 -0700, "Roger Shoaf"

But, mechanically, "how" does it float. You almost answered it below.

It took a little time for a friend and I to realize how a balloon floats. I think about half a Big Mac at McDonalds one day. You're correct here. It really puzzled me for awhile when I first noticed this phenonemen (sp). I have a lot of fun with kids when I tell them this, they usually go beserk and get real excited when they see it happen.
The reason why a balloon floats in still air is because of the pressure gradient between the top and the bottom of the balloon. Most people don't think there is enough of a gradient to make a balloon float but there is. They usually think of pressure drops between sea level and the top of a mountain, not one over just a foot of height. If the pressure was the same it would sink.
John
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snipped-for-privacy@asdfasdfsdffff.com (John Flanagan) writes:

The only way that there would *not* be a pressure gradient across the height of the balloon is if the material outside the balloon has zero weight. This would happen only if there's no mass (i.e. a vacuum), or if there's no apparent gravity (i.e. inside the orbiting space station). If the material around the balloon does have weight, any weight, then there must be a pressure gradient equal and opposite to the weight - or the air wouldn't be at rest.
There's also a pressure gradient inside the balloon. Gravity is the same inside and outside the balloon, but the density of helium is less than air, so the pressure gradient is less inside than outside.
Dave
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The pressure differential is only half of the equation. It has to be balanced against the weight of the balloon. In the case of a helium-filled balloon that rises, the net force resulting from the pressure differential is greater than the weight of the balloon, so it pushes the balloon up. For an air-filled balloon, the weight of the balloon is greater than the resultant buoyant force, so the balloon sinks.
The amount of force involved is not as tiny as you think. At sea level at 59 deg F, the pressure gradient is about 0.000531 psi / ft, or 0.0765 psf / ft. To simplify calculations, let's assume we have a balloon in the shape of a cube 1 ft on each side. The difference in the upward pressure acting on the bottom square foot and the downward pressure acting on the upper square foot is therefore 0.0765 lb, or 1.22 oz, acting in an upward direction. (Note that these numbers are the same as the weight of one cubic foot of air under these conditions -- this isn't a coincidence!) This force is greater than the combined weight of a cubic foot of helium (at near ambient pressure) and a balloon; it's less than the combined weight of a cubic foot of air and a balloon. (An empty balloon this size would probably weigh 1/3 to 1/2 oz, based on the weight of a smaller balloon I had lying around.)

The weight of the fluid displaced is simply an easily computed surrogate for the force due to the pressure differential. Both values turn out to be exactly the same (regardless of whether the fluid is compressible or not). But physically speaking, the balloon moves because of the forces acting on it, and the force acting on it due to the surrounding atmosphere is transmitted through pressure (which is the result of individual gas molecules impinging on the balloon).
Bert
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Very good description Bert.
John

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Momentum?
-c.

bubbles.
When
the
front
less
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snipped-for-privacy@asdfasdfsdffff.com (John Flanagan) wrote:

This is not true unless there's a hole in the balloon to allow the inside and outside pressures to equalize. As long as the balloon is sealed, the internal pressure can be anywhere from ambient atmospheric pressure up to the maximum (gauge) pressure the balloon can withstand. The internal pressure is balanced not only by the external pressure, but also by stresses in the material of the balloon. The same is true for basketballs and pneumatic tires.

This is generally true, but it doesn't mean that the final pressure is equal to the initial pressure, or that either one is equal to the ambient atmospheric pressure. The expansion will relieve some of the increased pressure differential, but not necessarily all of it. The amount will depend on the stress/strain characteristics of the balloon material.

The forces due to gravitational acceleration acting on the mass of air in the atmosphere results in a vertical pressure gradient (lower pressure at higher altitudes), which means the pressure acting on the top part of the balloon is lower than the pressure acting on the bottom part. Integrating those pressures over the surface of the balloon gives a net upward force (aka buoyant force). If the weight of the balloon is less than the buoyant force, the balloon will rise; if the weight is more than the buoyant force, it will sink; if the weight is exactly equal to the buoyant force, the balloon will stay where it is (but it's an unstable equilibrium).

The same as above, except that now we're talking about an acceleration due to braking instead of due to gravity, resulting in a horizontal pressure gradient instead of a vertical gradient. The balloon's mass multiplied by this acceleration presumably results in a horizontal "weight" which is less than the horizontal "buoyant" force, so the balloon "rises" (i.e., moves in the direction of the acceleration).
Bert
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LOL!
I guess I never did like fishing that much.
Jim
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com =================================================
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wrote:

According to this pressure curve, http://www.vernier.com/caliper/spring02/balloon.html the latex balloon pops at ~1.5 psi above ambient.
R, Tom Q.
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wrote:

Pressure curve for toy balloon: http://www.vernier.com/caliper/spring02/balloon.html
Danish (?) government study on toy balloons: http://www.balloonhq.com/faq/deco_releases/blnstudy.html
Maybe those Mylar balloons aren't Mylar: http://www.floralandballooncity.com/home/faq/faquest.htm
Miscellaneous facts about latex balloons: http://www.balloonhq.com/faq/science.html
R, Tom Q.
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wrote something ......and in reply I say!:

It will go past a maximum point, because as the balloon stretches, it becomes weaker and therefore requires less PSI to expand, but inside will always be higher than outside pressure. ****************************************************************************************** Huh! Old age!. You may hate it, but let me tell you, you can't get by for long without it!
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