PROPELLERS: The surface of a propeller blade is curved so that the blade has the shape of an airfoil. Water flows around the blade as it rotates, moving faster over the front surface. The faster motion lowers the water pressure on the front of the blade, and the blade is sucked forward.

WATER FLOW
As the blades of a propeller spin, they strike the water and make it move back. The force with which the blades move the water is called the "action". The water pushes back on the blades as the propeller begins to move, producing an equal force called "reaction" - which drives the propeller forward.

ACTION, REACTION and SUCTION
The combination of reaction and suction drives the spinning propeller through the water.
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