A lift counterweight is a heavy concrete, steel or cast-iron mass used in a lift system to balance the weight of the elevator car and reduce the energy needed to move it. The lift car and the counterweight are connected by steel hoist ropes passing over a motor driven pulley (known as a traction sheave). When the lift car goes up, the counterweight goes down and vice versa, balancing both the weight of the empty car and 50% of its maximum passenger load, meaning the traction machine only needs to move the difference in weight, not the full load.