Rowing is the act of propelling a human-powered watercraft using the sweeping motions of oars to displace water and generate reactional propulsion. Rowing is functionally similar to paddling, but rowing requires oars to be mechanically attached to the boat, and the rower drives the oar like a lever, exerting force in the same direction as the boat's travel; while paddles are completely hand-held and have no attachment to the boat, and are driven like a cantilever, exerting force opposite to the intended direction of the boat.