Pulley is a kind of deformed lever, which belongs to a simple lever machine. In China, as early as the Warring States Period, there was a record about pulleys in the book Mo Jing. The pulley with the fixed central shaft is called the crown block, which is a deformed equal arm lever, and can change the direction of force without any effort. The pulley whose central axis moves with the weight is called the movable pulley, which is a deformed unequal arm lever, and can save half the force without changing the direction of the force. In practice, a certain number of moving pulleys and crown block are often combined into various pulley blocks. The pulley block can save labor and change the direction of force.
The differential pulley (commonly known as chain block) commonly used in factories is also a kind of pulley block. Pulley blocks are widely used in cranes, winches, elevators and other machinery.
The crown block itself does not move, which can change the direction of force.
Moving pulley can save energy through its own movement.
The moving pulley is a labor-saving lever, and the crown block is an equal arm lever.
Function: The former can save labor, and the latter can change the direction of force. But neither can save the job.