Suction

Suction is the force that a partial vacuum exerts upon a solid, liquid, or a gas.[1] Removing air from a space results in a lowered pressure, which can cause fluids to enter the space or produce adhesion.

When the pressure in one part of a system is reduced relative to another, the fluid in the higher pressure region will exert a force relative to the region of lowered pressure. 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. The increased volume of the chest cavity decreases the pressure inside, creating an imbalance with the ambient air pressure, resulting in suction.