Lift is the force pushing an object up in its fluid surroundings. In the case of planes and birds, lift is generated by flow over the wings which accelerates the fluid down and away from the wings to create a reaction force (lift) in the opposite direction. In the case of fish and submarines, a net vertical force may also be generated by flow over the body and fins in the case of fish or flow over the body and control surfaces/wings in the case of submarines.