This product uses a combination device that combines a fixed pulley and a movable pulley together called a pulley block. Features: it can save effort and change the direction of force. Different combinations of pulleys. Through the experiment of detecting the change of tension by spring balance, it is understood that the movable pulley is essentially one a lever that can save effort, the fixed pulley is essentially a lever with equal arms, and the pulley block is more labor-saving and other principles and applications in real life.