sucking

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.
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.

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