In science, a vacuum is a volume that contains little or no matter. In other words, a vacuum is a region with an extremely low pressure. The word “vacuum” comes from the Latin word vacuus, meaning “empty.” A vacuum may occur naturally or be produced by pumping air out of a container or using fluid flow to reduce pressure (Bernoulli’s principle).
Partial Vacuum vs Perfect Vacuum
In the real world, a vacuum is partial or imperfect. A few atoms or molecules always remain. The pressure of a partial vacuum is lower than atmospheric pressure, but isn’t zero. A perfect vacuum is a theoretical space completely devoid of matter. This type of vacuum also goes by the name “free space.”
Examples of a Vacuum
Any region with a pressure lower than atmospheric pressure is vacuum. Here are examples of a vacuum:
- The inside of an incandescent lightbulb is a vacuum.
- Space is a near-perfect vacuum.
- The thin atmospheres of the Moon, Mercury, and Mars are a vacuum (at least compared to Earth).
- Suction from a vacuum cleaner forms a vacuum.
- The insulating area between the glass walls of a thermos contain a vacuum.
- The Earth’s thermosphere is a vacuum.
- A strong hurricane’s low pressure is a partial vacuum.
Comparing Different Vacuums
Here is a comparison of the number of particles per unit volume in different types of vacuums:
|Pressure||Molecules per cm3|
|Standard atmosphere (not a vacuum)||101.325 kPa||2.5×1019|
|Strong hurricane||87 to 95 kPa||1019|
|Vacuum cleaner||~80 kPa||1019|
|Liquid ring vacuum pump||~3.2 kPa||1018|
|Martian atmosphere||1.155 kPa to 0.03 kPa|
|Incandescent light bulb||10 to 1 Pa||1015 to 1014|
|Thermos||1 to 0.1 Pa||1014 to 1012|
|Earth’s thermosphere||as low as 10−7 Pa||107|
|Vacuum tube||10−5 to 10−8 Pa||109 to 106|
|Molecular Beam Epitaxy (MBE) chamber||10−7 to10−9||107 to 105|
|Interplanetary space||almost 0||11|
|Interstellar space||almost 0||1|
|Intergalactic space||almost 0||10−6|
The closest you can get to a vacuum in a laboratory is around 13 pPa, but a cryogenic vacuum system can achieve pressure as low as 5×10−17 torr or 6.7 fPa.
Humans can recover from exposure to a vacuum lasting 90 seconds or less. Plants can last about 30 minutes. A tardigrade survives in a vacuum for days or weeks!
Easy Ways to Make a Vacuum
The best vacuums use expensive pumps to remove gases. But, it’s easy to make a vacuum yourself using common materials:
- Attach a suction cup to a window. Pull back on the suction cup. The space between the cup and the glass is a vacuum.
- Cap the end of an empty syringe to seal it. Pull up on the plunger. The empty volume within the syringe is a vacuum. If the syringe contains a bit of water, the low pressure makes it boil.
- Attach the hose of the vacuum cleaner to a rigid, otherwise sealed container. The appliance sucks out the air, leaving an imperfect vacuum.
- Breathing creates a partial vacuum. When your diaphragm drops, the increase in volume decreases pressure inside the alveoli of the lungs. The pressure difference leads to inhalation.
- If you have access to a laboratory, a vacuum filter uses water flow to remove air from a flask. The inside of the flask is a partial vacuum.
Why Is Space a Vacuum?
Gravity is the reason space is a near-perfect vacuum. Over time, gravity draws particles of matter together, forming gas clouds, stars, and planets. The expanses between interstellar objects are left almost empty. Also, the Universe is expanding. Even without gravity, the space between particles increases.
- Chambers, Austin (2004). Modern Vacuum Physics. Boca Raton: CRC Press. ISBN 978-0-8493-2438-3.
- Genz, Henning (1994). Nothingness, the Science of Empty Space (translated from German by Karin Heusch ed.). New York: Perseus Book Publishing (published 1999). ISBN 978-0-7382-0610-3.
- Harris, Nigel S. (1989). Modern Vacuum Practice. McGraw-Hill. ISBN 978-0-07-707099-1.
- Ishimaru, H (1989). “Ultimate Pressure of the Order of 10−13 torr in an Aluminum Alloy Vacuum Chamber”. Journal of Vacuum Science and Technology. 7 (3–II): 2439–2442. doi:10.1116/1.575916
- Wheeler, R.M.; Wehkamp, C.A.; Stasiak, M.A.; Dixon, M.A.; Rygalov, V.Y. (2011). “Plants survive rapid decompression: Implications for bioregenerative life support”. Advances in Space Research. 47 (9): 1600–1607. doi:10.1016/j.asr.2010.12.017