Construction of Crane Pulley

The pulley is borne by two ropes, that is, each rope bears the object and the pulley force is a fraction of the total weight of the object and the pulley, the principle is: when n is odd, the rope starts from the pulley. There are three lengths of rope with one pulley, and then two lengths of rope are added for each additional pulley. For example: n=5, two pulleys (3+2) are needed. When n is even, the rope starts from the fixed pulley, and all the moving pulleys are carried by only two lengths of rope. For example: n=4, two pulleys (2+2) are needed.

The fixed pulley is essentially an equal arm lever, which does not save effort or effort, but can change the direction of the force. It is not easy to pull the hook weight by fixing the pulley. The reading on the spring scale is the same with or without the fixed pulley. It can be seen that the use of fixed pulley does not save effort but can change the direction of the force. In many cases, changing the direction of the force will bring convenience to the work. The principle of fixed pulley: the essence of fixed pulley is an equal arm lever, the power L1, the resistance L2 arm are equal to the radius of the pulley. According to the balance condition of the lever, it can also be concluded that the fixed pulley is not labor-saving

Block: A block consisting of a fixed block and a moving block, which saves effort and changes the direction of the force. The block holds the object by several lengths of rope, and the force used to lift the object is a fraction of the total weight. Although the use of pulley block saves force, it costs distance, and the distance of power movement is greater than the distance of heavy objects.