4 ms·
It is unclear how strong a vacuum Guericke's pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have
by yesenadam 8y ago
It is unclear how strong a vacuum Guericke's pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have been held together with a force of around 20 000 N (4400 lbf, or 2.2 short tons)
I'm no expert, but if it was able to evacuate all of the air from the inside sounds unlikely - impossible, even. What's the best we could do nowadays? How total are (practical) vacuums?
- jessriedel 8y agoEvvacuating 99.9999% of the air is technologically much harder than merely 95% of it, but the difference in the force exherted on the spheres is small (only 5%).
- yesenadam 8y agoThanks. Well, that is extremely counter-intuitive.
- mirimir 8y agoSimple mechanical vacuum pumps can reach ~1 mbar (0.001 atmosphere).[0] I doubt that Guericke's pump could reach even 100 mbar, but that's only 10% of atmospheric pressure. So the force to separate the hemispheres would have been only ~2 short tons. That's still a lot, however. The best multistage pumps can reach ~0.0001 mbar.[0] Generally, attainable vacuum by pumping depends on leakage rate vs pump speed, and also on the vapor pressures of components. Such as oil used for lubrication, grease for sealing, rubber or plastic hoses, etc. So for a high vacuum system, you want just metal and glass, and you want them to be very clean. Fingerprints are a huge issue. Also, you typically put a cold trap between your pump and the working volume. Both to get lower pressure, and to avoid contamination. For low vacuum, dry ice in acetone is OK. Then liquid nitrogen, and finally liquid helium. 0) https://cds.cern.ch/record/1046850/files/p43.pdf https://cds.cern.ch/record/1046850/files/p43.pdf Edit: It's important to avoid contamination of the working volume (say, by pump oil) and of the pump (say, by water, or corrosive substances).
- posterboy 8y agoI think it's more illustrative to think of atoms/molecules per cubic meter. If I remember correctly, 1 or 0.1 µbar is proportional to around 1 atom per cubic meter.
- jonsen 8y agoThat’s a lot of pressure made by one tiny little atom. I can’t believe that.
- jws 8y ago3x10^22 atoms per cubic meter of air. That micro is going to make it 3x10^16 atoms.
- jonsen 8y agoSo 1 atom per cubic micrometer is about right for 0.1 microbar.
- TheSpiceIsLife 8y agoOne cubic micrometer is 1mm³ right?
- jonsen 8y agoOne cubic micrometer is 1µm³. One cubic millimeter is 1mm³.
- TheSpiceIsLife 8y agoOh yeah, duh. Thanks.
- mirimir 8y agoRight, a cubic micrometer is 1E-18 cubic meter. So there are ~2.5 molecules per cubic micrometer at ~0.1 microbar.