When the engine is started, the engine flywheel turns the converter housing, which rotates the impeller. As the impeller turns, oil is forced toward the outside edge, changing mechanical power into hydraulic power. The rounded profile of the impeller, along with centrifugal force, moves the oil outward and across into the turbine. Oil striking the turbine blades transfers hydraulic power and rotates the turbine. The motion of the turbine converts the hydraulic power back into mechanical again and turns the output shaft.