Glass Windows and Vaccuums?
I am learning about pressure in science class and I have a question about pressure on windows. In normal life, air pressure doesn’t collapse a window because it is pushing on it from all sides. However, I once saw a demonstration at a museum of a very small vaccuum in which a science experiment was performed. The sides were all made out of glass. Since the inside was a vaccuum, there was no air pressure inside it. Why didn’t the air crush the vaccuum canister? Is it possible to simply manafacture glass strong enough to resist that pressure? A good, scientifically backed answer will be appreciated.
Highway
on February 6th, 2012
strength of glass comes from thickness and distance between supports
the glass may have been thick
it may have been poly carbonate
it may have been a small window
absolute vacuum is roughly -15 psi. so a letter size window will have about 1000 pounds pushing against it. Stong piece of glass. Or perhaps it was only a slight vacuum, 1 or 2 psi
FuzzyFerret
on February 6th, 2012
Hey, in a window, the inside part of the window has a thin layer of air. It is not vacuum
ToxicSkull
on February 6th, 2012
perfect vacuums cant be created the vacuum u saw had pressure of at the least 10^-17 Pa
Style
on February 6th, 2012
A column of air, 1 square inch in cross section, measured from sea level to the top of the atmosphere would weigh approximately 14.7 lb… so the glass would only need to be strong enough to withold 14.7 lb/inch or surface area.
WyleCoyote
on February 6th, 2012
ya glass can be so strong as u see in bullet proof glass which can resist the pressure of bullet.
also it depends that how much vacuum u applied
SkateRForeveR
on February 6th, 2012
Yes it is possible to build glass strong enough to resist the resultant pressure, that is approx101KPa (normal air pressure) minus the pressure inside as there is no perfect vacuum on earth. The structure must be strong enough to resist this. The force on the outside of one of the surfaces is proportional to its surface area, its strength increases indefinitely with wall thickness, although I have not calculated the requred thickness, it is definitely feasible.
Fractalfallout
on February 6th, 2012
Firstly, the vacuum was not a perfect vacuum, there will still have been a very small air pressure inside the glass.
Secondly, the shape of the glass will have been a factor in its withstanding of pressure. Bell jars are frequently used in experiments with vacuums inside them, as the shape adds structural support to the glass with low pressure inside.
Thirdly, glass can be manufactured sufficiently thick and dense to withstand vacuums created in these kind of experiments. Consider the existance of bulletproof glass also, it can be quite a strong medium.
Finally, it is worth noting that inside double and triple glazed windows, there is a thin layer of vacuum in between each layer, which is what makes them such effective insulators, as no sound can pass through the vacuum and heat can only pass through as radiation. They do, of course, not break under the pressure of these small vacuums.