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Vacuum

In physics, a vacuum is the absence of matter (molecules, atoms...) in a volume of space. A partial vacuum is expressed in pressure units. The SI unit of pressure is pascal (Pa). It can also be expressed as a percentage of atmospheric pressure using the bar or barometer scale.

Table of contents

1 Degrees of vacuum 2 Creating a vacuum 3 The quantum-mechanical vacuum 4 See also 5 External links

Degrees of vacuum

• atmospheric pressure = 760 torr or 100 kPa
• vacuum cleaner = around 300 torr or 40 kPa
• mechanical vacuum pump = around 10 millitorr or 1.3 Pa
• near earth outer space = around 10^-6 torr or 130 μPa
• pressure on the Moon = around 10^-8 torr or 1.3 μPa
• cryopumped MBE chamber = 10^-9 - 10^-11 torr
• interstellar space = around 10^-10 torr or 13 nPa

At this stage, the system has entered a state called molecular flow, where the velocity of each molecule is approximately random. Methods to remove the remaining gas include:

1. Converting the molecules of gas to their solid phase by freezing them, called cryopumping or cryotrapping
2. Converting them to solids by electrically combining them with other materials, called ion pumping
3. Use of another specialized pump. Examples are turbomolecular pump or diffusion pump.

The quantum-mechanical vacuum

See also

• Vacuum pump
• Pressure
• sucking.

• Journal of Vacuum Science and Technology A

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