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. Suction is popularly thought of as an attractive effect, which is incorrect since vacuums do not innately attract matter. Dust is “sucked” into a vacuum cleaner when it is pushed in by the higher pressure air on the outside of the cleaner. The higher pressure of the surrounding fluid can push matter into a vacuum but a vacuum cannot attract matter.
This is similar to what happens when humans breathe or drink through a straw. Both breathing and using a straw involve contracting your diaphragm and muscles around your rib cage. The increased area in your chest cavity decreases the pressure inside creating an imbalance with the ambient air pressure, or atmospheric pressure. This imbalance results in air being pushed into your lungs or liquid being pushed up into a straw and into your mouth.
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