A simple machine that can rotate around the central axis by rotating the disc of a groove and the rope, duct tape, cables, chains, etc., which can be rotated around the central axis.
The pulley is the deformation of the lever, which belongs to the simple machinery of the lever class.
In our country early in the warring states period of the book "the ink classics" in the record of the pulley.
The fixed and fixed pulley of the central axis is called a fixed pulley, which is a shape-shifting lever, which can change the direction of the force.
The pulley, which is moved by the center axis and the weight, is called a pulley. It is a deformation of unequal arms, which can save half of the force, but not change the direction of the force.
In practice, a certain number of movable pulley and fixed pulley can be combined into various forms of pulley block.
The pulley block has both the power and the ability to change the direction of the force.
The commonly used differential pulley in the factory is also a pulley block.
The pulley block is widely used in crane, hoist, elevator, etc.
There are two kinds of pulleys: fixed pulley and movable pulley
(1) the fixed pulley is essentially equal to the arm lever, not saving effort or effort, but it can change the direction of the force.
The characteristics of the pulley
It is not easy to pull a hook code through a pulley.
The reading of the spring scale is the same with or without the fixed pulley.
So you can see that using the fixed pulley doesn't save you a lot of effort but you can change the direction of the force.
In many cases, changing direction will bring convenience to work.
The principle of fixed pulley
The fixed pulley is essentially an equal arm lever, and the power L1, the resistance L2 arm is equal to the pulley radius.
According to the leverage equilibrium conditions, it can also be concluded that the fixed pulley is not efficient.
(2) the movable pulley is essentially the lever of the power arm, which is twice the lever of the resistance arm, and the province 1/2 power is twice the distance.
The characteristic of movable pulley
Using movable pulley can save half force and distance.
This is because the hook code is hung from two pieces of rope when using a movable pulley, and each piece is only half the weight of the hook.
Although the use of movable pulley saves the force, but the distance of the dynamic movement is greater than the distance of the hook code, namely, the distance.
The principle of movable pulley
The movable pulley is essentially a power arm (L1) for the lever arm (L2).
(3) pulley block: the pulley block consisting of the fixed pulley and the movable pulley, which is both labor-saving and changing the direction of the force.
Block and tackle with some rope hanging object, lift force used is a fraction of the total weight. Count the free end of the rope around the block a, and bypass the crown block is not.
Although the use of the pulley block, it saves the force, but the distance is greater than the distance that the weight moves.
Use of the pulley block:
In order to both save and change the direction of power, the fixed pulley and the movable pulley can be combined into the pulley block.
The size of the province
When using the pulley block, the pulley group USES a few pieces of rope to hang the object, and the force used to lift the object is a fraction of the weight.
Features of the pulley block
It is easy to see that using the pulley block, although the use of the pulley block has saved the force, the distance from the dynamic movement is greater than the distance of the cargo.