h a l f b a k e r yVeni, vidi, teenie weenie yellow polka dot bikini.
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A little googling around says pingpong balls can withstand 70m depth pressure, so 1bar is hardly going to bother them. |
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I doubt it would be LTA. But 2 - 1 bar is the same as 1 - 0 bar. |
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A football that starts at 2|1 will equalize at half its volume. A football that starts at 7|1 will equalize at 1/7 its volume. A football that starts at x|0 will be a pancake. |
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Good thing it's not a football and won't collapse under a measly 1bar differential. |
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I'm pretty sure I could put 14pounds on top of a pingpong ball and, even though it's a point contact instead of a full square inch, I doubt it would buckle. |
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I'm with the critics on this one, and I got here too late to be the initial poster, but pending some empirical evidence it's skeptics 2, protagonist 1. |
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Consider a hollow sphere with internal pressure of 1 Bar. |
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Increase the external pressure from 1 Bar to 1.1 Bar. The
sphere deforms slightly, decreasing its internal volume. At
constant temperature, the internal pressure must rise, as defined
by the General Gas Law. |
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This change in internal pressure resists the external pressure and
the deformation ceases. |
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If the sphere is evacuated, and in a vacuum, then the system is
stable. Increasing the external pressure will be resisted only by
the shell, as there is no internal gas to compress. Once the shell's
strength is exceeded, the sphere collapses. |
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Oh, and you owe us for a new ping-pong ball ... |
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Reducing something by nothing is way different to taking everything away to get nothing. 1 going down to 0 not 1 - 0 |
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I think [8th]'s analysis is wrong, as is [bigs]'s. |
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For a thin-walled spherical container like a ping pong ball, the failure mode is catastrophic buckling. Basically, a perfect spherical shell, subjected to a uniform pressure, would withstand a very large force. But as soon as it buckles (for instance, due to one point on the surface being indented by a non-uniform pressure), then it will fail catastrophically - it's the spherical analogue of Euler buckling. |
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With that in mind, if a ping pong ball can withstand 70m of water (about 7atm, or 6atm over internal pressure), it should equally well withstand an internal vacuum in air (1atm). In either case, tapping the ball so as to cause a local deformation would lead to an immediate collapse. |
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//uniform// a) not a reality b) wouldn't the two situations be different because of the variation in populations of pressure elements due to more non element and ping pong interactions. More even pressure? |
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[xg] this post is celluloid spheres, not metal bricks. Both shape and material properties are defining features. |
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<link> vid of somebody evacuating a ping-pong ball for some unrelated nefarious purpose. |
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Unsurprisingly, it doesn't implode. |
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It's actually a very interesting question as to the failure mode of
a spherical container between absolute pressure and relative
pressure . |
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Case (a): Sphere is evacuated and sealed, extenal pressure is
increased until collapse occurs. |
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Case (b): Sphere is pressurized in equilibrium with its
environment and sealed, extenal pressure increased until
collapse occurs. |
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Will the failure modes be identical, at the same differential
pressure ? This is not a rhetorical question . |
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The only difference is that the evacuated ping pong ball will collapse more thoroughly than the air-filled one because, in the latter case, the internal pressure will at some point match the external pressure as the ball collapses. |
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I agree that ping-pong balls generally won't collapse with a
vacuum. However I expect that gas will slowly seep through
the balls, reducing the insulation effect after a couple
months and/or years. |
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The idea was borne of considering an insulation for a double-wall volume, that would be disposable/recycleable : just suck out the old after ten years and replace with new. Most of the "material" is after all vacuum; materiel-wise not very expensive. Perhaps, like spray-in foam, the spheres could be produced on-site. |
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In the specific case of traditional celluloid ping pong balls, I'm surprised the Borg hasn't chipped in a pastry, given the insulation would start off highly flammable (and mostly immune to fire retardants) and age into a low-yield explosive as the camphor outgassed/sweated out of the nitrocellulose. The new polyester balls aren't quite so interesting. |
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Perhaps glass spheres - slightly thicker-shelled Christmas ornaments - instead. That should last a half-century or so. |
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Is the minimal equipment needed to go from 2 to 1 bar, the same equipment for going from 1 bar downto 0 bar? Of course the equipment that will do 0 bar with do the other. I always thought that you needed better equipment to get a better zero. |
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//The only difference is that the evacuated ping pong ball will collapse more thoroughly than the air-filled one because, in the latter case, the internal pressure will at some point match the external pressure as the ball collapses.// |
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Why not old unused glass lightbulbs? |
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At some strength, the pingpong ball would resist pressure
even if the term goes to 0. 1 atmosphere remains just one
atmosphere. |
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If it was a perfect sphere, potentially the plastic
pingpongball would be able to resist. |
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The real question here is how would it be to play ping pong with evacuated play ping balls? They would be lighter (in air) than the air-filled ones. |
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By the way, this reminds me of the legendary vacuum blimps, which is what got me into the halfbakery oh so many years ago. Wanted: Vacuum Dirigible Service Tech |
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//Is the minimal equipment needed to go from 2 to 1 bar, the same equipment for going from 1 bar downto 0 bar?// |
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Sealing aside, all that needs be done is supply a force greater than 14.7lb per square inch cross-section of the evacuation hose/pipe. |
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Not an insurmountable problem - after all, it's easy enough to
get the basic material for a very nice, warm sealskin coat ... if,
that is, you all club together ... |
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Have you considered kitten? |
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