Suction

Suction is the day-to-day term for the movement of gases or liquids along a pressure gradient with the implication that the movement occurs because the lower pressure pulls the gas or liquid.

If all gas or fluid is removed the result is a perfect vacuum in which the pressure is zero.

Pressure reduction may be static, as in a piston and cylinder arrangement, or dynamic, as in the case of a vacuum cleaner when air flow results in a reduced pressure region.

When animals breathe, the diaphragm and muscles around the rib cage cause a change of volume in the lungs.

A common semantic mistake is made when in case of accidents with spaceships or aircraft in which objects are blown out of the vessel in the case of an uncontrolled decompression which is often wrongly referred to as objects being sucked out.

Gasses or liquids that move along a pressure gradient can exert forces on objects. Objects can only be pushed by gases or liquids. The correct terminology used depends on whether they are pushed from a pressurized zone towards ambient pressure (blown out) or from ambient pressure towards a low pressure zone (sucked in). Gases and liquids cannot generate pulling forces on objects. [ 1 ]