Explaining How Air Weighs in an Evacuated Flask

[Integral]

If you are dealing with "real" rubber ballons you will find that a He filled balloon will relativly quickly (24hrs) sink, where a balloon made of mylar will float for days or even weeks. He is small enough that it will pass through the pores of a rubber ballloon, thus the loss of buoyancy. A similar balloon filled with H would loose bouancy even faster then He.

There is also the fun part of H, that is its love affair with O₂.

 

[Mk]

So... if you want a balloon that will stay up forever you get a mylar one and fill it up with krypton!

 

[MR. P]

ok what volume would a vacuum have to have in order to lift a 200 pound person assuming a weightless container 100 feet above sea level?




frank

 

[nishant]

what if this air in the first place in the jar is by some method changed into a macromolecular colloid,should we not be taking the force resulting from the collisions

 

[SpaceTiger]

ok what volume would a vacuum have to have in order to lift a 200 pound person assuming a weightless container 100 feet above sea level?

You'd need to displace 200 lbs of air:

$$V=\frac{W}{g\rho_{air}}$$

where W is 200 lbs, g is the gravitational acceleration, and $$\rho_{air}$$ is the mass density of air at that height above sea level. It's about 100,000 liters.

 

[MR. P]

thanks spacetiger i'll mull that for awhile ,got to go to work now...do you know much about light?




frank

 

[SpaceTiger]

thanks spacetiger i'll mull that for awhile

Keep in mind that it was thought of long ago that buoyancy could be used to carry human beings. It's the same principle behind hot air balloons. Why is it the same? Consider the ideal gas law again:

$$P=nkT$$

If you fill a balloon with normal air, it will have the same density as its surroundings and not go anywhere. If you heat it, however, then in order to maintain pressure balance with its surroundings, the above equation says that the number density must go down. If the number density is going down, then Archimedes' principle says that there must be a buoyancy force.

I would expect this means of lifting oneself would be much easier than trying to create a controlled vacuum (you'd want to change its density in flight) inside of a solid object.

,got to go to work now...do you know much about light?

A good bit. I am an astronomer, remember?

 

[MR. P]

The most important piece of advice [for aspiring physicists] is to keep your sense of wonderment alive - Dr. Michio Kaku

ST I would have thought you would be interested in any means available to view the cosmos from 150,000 feet...think of the discoveries awaiting your eye...or adaptive array..at 150,000 feet that'd be almost like the opportunities that existed for Gallieo...re: your assumption of a rigid structure for isolating a vacuum , good for a quickie evaluation , however the premiss yields myriad opportunities for taming the impractical and the impossible, even more exciting , the ultimate solution for 'bouyancy'
or completing the logic sequence:

question...What is lighter than Helium?
answer...Hydrogen.
question...What is lighter than Hydrogen?
answer...Nothing.
question...What is another way of describing 'nothing'?
answer...A vacuum or the absence of something.
question...Is a vacuum the lightest?
answer...YES!
Therefore , since 'vacuum' is the lightest, then it appears that confining 'vacuum' is merely an 'engineering' problem!

To that end , the premiss does not have to be predicated upon a 'rigid body' confinement mechanism. and when 'on station' maintaining a 'vacuum' in a rareified environment , as exists in the Stratosphere, would be the most energy efficient option of all other possibilities, intuitively.

 

[MR. P]

somehow that got posted before i could edit it...Anyway ST , that's what has been driving those elementary questions...I have been building/experimenting with 'tensegral' structures and for the last ten or twelve years specifically 'tetrahedrons' or more affectionately 'TETS' and most recently my latest configuration I call my 'TET Offensive'. An extreme volume whose boundries (amorphic) are defined by the mass to be managed. This structure is closely analoguous to a lung or a dendritic neural form. I will be posting pictures on our site as we continue to build/present our different pursuits...

What you have thought or believed to be a lack of focus has always been the denial of BOREDOM and the pursuit of enlightenment...fap

If you can ask the question then you 'beg' the answer...ukn

frank MR. P

 

[SpaceTiger]

ST I would have thought you would be interested in any means available to view the cosmos from 150,000 feet...

That's quite a height. Assuming an exponential drop in density with a 7 km scale height, the density there should be less than 1% of its surface value. That means that, in order to get the same buoyancy force, you're going to have to make your volume at least 100 times larger than the above number.

 

[MR. P]

Indeed, ST, not an insurmountable engineering problem. At CalTech they are investigating 'intelligent' algorythms or optimizing algorythms for 'Chain Linked' 'nanobots'.In the case of an amorphic vacuum confining structure the algorythm would be optimizing for volume to mass emphasizing volume over mass. In all of these cases the barrier 'thickness' is undefined to facilitate optimization of the physical properties of the structural elements. For example..if the physical properties favor compressional strength over tensile strength then the adaptive algorythm would create a structure totally different in appearance from one composed of tensile elements. Arguably, I am inclined to favor a tensile archecture over a compressional form primairly because tensile forms tend to be more delicate/beautiful in my opinion especially for the environments I'm looking toward.
I do appreciate the repartee...

frank