<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2011) (Learn how and when to remove this template message) </Td> </Tr> <P> Suction is the flow of a fluid into a partial vacuum, or region of low pressure . The pressure gradient between this region and the ambient pressure will propel matter toward the low pressure area . Dust is sucked into a vacuum cleaner when it is pushed in by the higher pressure air on the outside of the cleaner . </P> <P> This is similar to what happens when humans breathe or drink through a straw . Both breathing and using a straw involve contracting the diaphragm and muscles around the rib cage . The increased volume in the chest cavity decreases the pressure inside, creating an imbalance with the ambient air pressure, or atmospheric pressure . This imbalance results in air pushing into the lungs or liquid pushing up through a straw and into the mouth . </P> <P> Pumps typically have an inlet where the fluid (or air) enters the pump and an outlet where the fluid / air comes out . The inlet location is said to be at the suction side of the pump . The outlet location is said to be at the discharge side of the pump . Operation of the pump creates suction (a lower pressure) at the suction side so that fluid / air can enter the pump through the inlet . Pump operation also causes higher pressure at the discharge side by forcing the fluid / air out at the outlet . There may be pressure sensing devices at the pump's suction and / or discharge sides which control the operation of the pump . For example, if the suction pressure of a centrifugal pump is too high, a device may trigger the fluid pump to shut off to keep it from running dry; i.e. with no fluid entering . </P>

How are breathing and drinking through a straw examples of negative pressure
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