Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: cornemuse on 22/10/2016 16:21:54
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If you have a balloon at sea level for instance that is 12" diameter, how much air would be needed it to achieve the same diameter in the vacuum of space?
-cornemuse-
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If you have a balloon at sea level for instance that is 12" diameter, how much air would be needed it to achieve the same diameter in the vacuum of space?
-cornemuse-
This depends on the material the balloon is made of. If it is made of some material like mylar, then all that is needed for the air inside to be at same or slightly above the outside air pressure. This means that this type of balloon would need very little interior air to keep its shape.
On the other hand, with a typical rubber balloon, the air inside has to exert a pressure against the elasticity of the balloon material. This means It takes more pressure inside than outside, and assuming the same temp, higher air density inside than outside. Such a balloon would need to have a certain air pressure inside even when placed in a vacuum. How much pressure depends upon the properties of the material and by how much the 12" diameter exceeds the natural "non-inflated" diameter of the balloon.
So there is no one answer, as it depends on a number of factors.
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Although a theoretical calculation would be difficult an experiment would be simple, inflate the balloon with a pressure meter attached to the required volume and note the reading of the meter.
The meter will read the difference in pressure between the atmosphere and the air inside the.
balloon, that is the quantity of air that would be required if you were in space.
Air at normal pressure and temperature weighs about .00125Kg/m^3 so if the pressure of the air needed to in inflate the balloon to the required diameter was 10% above atmospheric pressure the amount of air required would be 0.125 Grams per m^3.
You measure or calculate the volume of the inflated balloon and multiply by this factor
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The Children's Gallery at the London Science Museum used to have a very simple demonstration of a doorbell and a balloon inside a bell jar that was gradually evacuated. The balloon was initially "soggy", measuring about one inch in diameter. As the air was pumped out of the jar, so the sound of the bell became fainter and the balloon swelled up to about 9 inches diameter.
A thinner balloon could well have become larger, but when I was involved in making displays for the LondSciMus I was given the specification "it must work for 50 years without maintenance and be fixable by a man with a hammer when it breaks", so I guess they used a pretty tough ballooin.