What is Vacuum Pressure?

Do vacuums suck?

In looking for answers, you might start with the Webster’s dictionary definition of vacuum:

  1. The emptiness of space
  2. A space devoid of matter
  3. A state of isolation from outside influences
  4. A space partially exhausted by artificial means
  5. A device creating or utilizing partial vacuum, to draw or take in by or as if by suction

Definitions and b refer to a perfect vacuum. Definition c is a metaphor referring to the perfect test environment. Definition d refers to a partial vacuum. Finally, definition e, is simply the appliance we clean our floors with - a vacuum cleaner. These definitions don’t seem to relate vacuum to suction and in the pressure technology industry, vacuum refers to a state with an absolute pressure reading of 0 psi.

So, why is there a perception that vacuums suck?

When a pressure gradient exists, particles from a higher pressure area rush into a low pressure area. You may have heard the phrase "nature abhors a vacuum."

Imagine a closed box with a gas in it, with an initial state where all the molecules are in one corner of the box, trapped by an invisible force field. The particles inside the force field are randomly bouncing off each other, the container, and the field. The moment the force field is turned off there is nothing to bounce off in the direction of the force field so the particles move in the direction where they have no resistance in their movement. Almost instantaneously the pressure in the box will be equal in every sector. The particles are not sucked in to the vacuous area; they move there because there is no resistance in that direction.

A full vacuum can be found in outer space where there is zero pressure. This is why people often refer to it as “the vacuum of space.” But does space have suction?


In science fiction there’s always a scene where a hatch unexpectedly opens and a space explorer gets “sucked” out into outer space. However, just like the box of molecules described above, molecules aren’t sucked out, but pushed out by all the other gas molecules also going in that direction. The vacuum outside their spacecraft causes the higher-pressure air inside to “blow” out, taking our space explorer with it.

Do vacuums really suck? The answer is technically no. 

There are just pressure gradients between one area and another. A vacuum, however, is simply an area with a pressure reading of zero.

Read 'What is Pressure? Definition and Types Explained' for more info.

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