Vacuum

For other uses, see vacuum cleaner and Vacuum (musical group).

Degrees of vacuum

• Atmospheric pressure = 101.3 kPa (760 Torr) or (760 mm in height under standard acceleration of gravity)
• Vacuum cleaner = approximately 80 kPa (600 Torr)
• Mechanical vacuum pump = approximately 100 Pa to 100 μPa (1 Torr to 10⁻⁶ Torr)
• Near earth outer space = approximately 100 μPa (10⁻⁶ Torr)
• Cryopumped MBE chamber = 100 nPa to 1 nPa (10⁻⁹ Torr to 10⁻¹¹ Torr)
• Pressure on the Moon = approximately 1 nPa (10⁻¹¹ Torr)
• Interstellar space = approximately 1 fPa (10⁻¹⁷ Torr)

As gas pressure decreases, the mean free path (MFP) of the gas molecules increases. When the MFP is greater than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics.

Related Topics:
Mean free path - Fluid mechanics

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In interplanetary and interstellar space, isotropic gas pressure is insignificant when compared to solar pressure, solar wind, and dynamic pressure. Astrophysicists prefer to use density to describe these environments, in units of particles per cubic metre.

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