How strong is the vacuum in space? If possible in mph, or other easy to understand measurements...as someone else asked, "if you took a bottle of air into space and opened it, where would it go?" I'm asking either at what speed would that air try to escape and/or how fast would the vacuum pull at it?


Vacuum or pressure is quantified in terms of bar or torr. 1 bar or 760 torr is roughly one atmosphere and in terms of vacuum measurement 1 mili-bar is taken as almost equal to 1 torr.

at 1 bar pressure and at room temperature the number of atoms per cc is ~$2\times 10^{19}$. The number of particles per cc in vacuum can range from $10^{-4}$ to $10^6$. The number is extremely small. At earth you can call it vacuum of $10^{-10}$ to $10^{-20}$ mbar.

These particles are a result of the gases/solar flares expelled by the stars.

As far as second part of your question concerns the velocity of the gas will be its thermal velocity. One side is at pressure P (~1 bar) and other side is practically 0. because 1 bar - $10^{-3}$ mbar is same as 1 bar -$10^{-23}$ mbar. If you take air jar in vacuum the particle velocity (mostly nitrogen) is around 400 m/sec.

I hope this will answer your query

You may find this article1 and article2 useful. The density calculation is calculated from Gas law and Avagrado number. 1 mole gas has volume of 22.4 liter at STP (760 torr and 300 K temp.) and it has $6.023\times10^{23}$ molecules.

YOu may find gas dynamics here

  • $\begingroup$ @hsinghal- please give a reference to your data please. $\endgroup$ – user5434678 Jun 8 '16 at 3:01
  • $\begingroup$ Not sure where you get the 4m/sec. At room temperature it's more like 500 m/sec, see teachastronomy.com/astropedia/article/Velocity-of-Gas-Particles . $\endgroup$ – Previous Jun 8 '16 at 3:56
  • $\begingroup$ @Previous Sorry I have miscalculated from 400 m/sec to 4 m/sec I have corrected the value, the difference between my calculations in the article given by you is due to the fact that he used $\frac{3}{2}kT$ as energy and I used $kT$ as energy, which is not much actually because we are doing order of magnitude calculations. $\endgroup$ – hsinghal Jun 8 '16 at 6:08

This is non-sequitur (vacuums / space does not suck). However, the answer is "it depends" ... it's about pressure differences.

Air moves towards a less pressurised state in nature unless something like gravity is forcing a rise in pressure (like in earths atmosphere).

Space is vacuum but that simply means "empty" (mostly) what it doesn't mean is "works like your vacuum cleaner".

We can observe this by taking a barometer from sea level to the top of a mountain and watching the pressure drop as we go, the higher you go the lower the pressure.

How fast that process happens is dependent on the amount of gravity applied at each point and how fast you travel (ever had your ears pop on a plane, that's the plane not pressurising at the same rate the pressure is dropping outside).

So assuming a container of air that was collected at or near sea level on earth the air pressure is approximately 14psi. When opening that in space (which is basically 0psi) there's a 14psi gap between the vastness of space and the air we just exposed to it inside our container.

The net result is that pressure difference will cause the air to rush out in an attempt to "equalise" those two pressures at a rate equal to a gradient from 14psi down to 0psi as the pressure inside the container drops.


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