CENTRIFUGAL FORCE
The centrifugal pump works in the same way as sucking on the straw. As the engine starts, the impeller turns which forces the water around it out of the pump's discharge port. The partial vacuum created, allows the earth's air pressure to force water up the suction hose (straw), and into the suction (inlet) side of the pump to replace the displaced water. When the water hits the rotating impeller, energy of the impeller is transferred to the water, forcing the water out (centrifugal force). The water is displaced outward, and more water can now enter the suction side of the pump to replace the displaced water.