Knowledge about pulleys Fixed pulleys Movable pulleys Characteristics of pulley blocks How to spare

1.The fixed pulley only changes the direction, and is generally used for simple lifting problems, such as the fixed pulley commonly used when people send things downstairs to the upstairs.

2.Movable pulleys only change the amount of force, i.e., reduce the force by half, and are often used in equipment that bears a large amount of weight.

3.Pulley blocks, on the other hand, are used in equipment that requires both change of direction and low effort.

4.One thing to keep in mind about the rope method is that the ropes must not intersect.

In fact, it is difficult to pull the pulley, as long as you master the decision, it is not difficult to pull at all. If there are fewer moving pulleys when the pulley group is in the line, then it is necessary to start from the fixed pulley first; On the contrary, if there are fewer pulleys, then we must start from the pulleys; If there are as many as the same, you still have to go around the pulley first. This is the most basic method, and there are many complex and changeable winding methods, which require you to pull slowly.

The fixed pulley is on the top and the movable pulley is on the bottom. The movable pulley saves half the force, and the movable pulley does not save the force, but it can change the direction of the force.

There are two ways to wind the rope of the pulley block:

First, the rope is first tied to the fixed hook of the fixed pulley, bypassing the movable pulley below, and then bypassing the fixed pulley above;

The second is that the rope is first tied to the fixed hook of the movable pulley, bypassing the fixed pulley, and then bypassing the movable pulley, and each pulley rope can only be wound once.

If the number of rope segments n is even, the fixed end of the rope is on the fixed pulley, and if the number of rope segments n is odd, the fixed end of the rope is on the movable pulley.

1. Fixed pulley, which is physically defined as a pulley with a fixed position of the shaft. Although the fixed pulley can not save force when it is used, it can change the direction of our force, and it also costs distance.

2. The fixed pulley is a kind of fixed pulley, and its fixation is not simply fixed and ignition, but the neutral beating mandrel of the pulley is fixed. The main advantage of the fixed pulley is that it can change the direction of the force, when we use the fixed pulley to pull a very heavy object, it is not very strong, but we can change the direction of the force through a fixed pulley to the direction we use very well, so that it is easy to pull the heavy object. The disadvantage of fixed pulley is that it cannot save effort.

In other words, the force we use to use the fixed pulley is the same as the force used to adapt to the fixed pulley. But we can overcome its shortcomings with a simple pulley set.

One. Definition. 1.Fixed pulley: the pulley with a fixed shaft, the effect, not saving force, can change the direction of force;

2.Movable pulley: a pulley whose shaft moves with the object, acts, saves half of the force, and does not change the direction of the force;

3.Pulley group: movable pulley and fixed pulley group lift the reed together, start from the movable pulley and wind, which is an odd number; Starting from the fixed pulley is an even number.

Two. Force analysis.

1.Fixed pulley.

Force analysis, f=g, using the principle of the bar is f2*l2=f1*l1, the f is equal to the gravity of the weight, and the fixed pulley can change the direction of the force, but it is not labor-saving.

2.Movable pulleys.

Force analysis, using the principle of starvation lever, the fulcrum is then o point, f1 * l1 = f2 * l2, l1 = 2l2, so f1 = 2f2. Movable pulleys can save effort, but they cannot change the direction of force. The force travels twice as far as the object travels. <>

1.Fixed pulley.

1) Take-off and landing machines used in the construction site;

2) Home elevators;

3) pulleys on the flagpole;

4) Curtain pulling;

5) Machines for moving rice.

2.Movable pulleys.

1) Hanging people outside the wall during decoration;

2) the lifting of the sails;

3) pulleys for cable cars;

4) pulleys of cranes;

5) Fishing rods.

3.Pulley Block:

1) boom; 2) Lifts;

3) Crane;

4) winch;

5) The front and rear wheels of the bicycle are connected.

Fixed pulley: rice conveyor, home elevator, flag raising, curtain, crane.

Movable pulleys: hoisting, fitness equipment, sails, cable cars, cranes.

Pulley block: tower crane, boom, lift, crane, winch,

Fixed pulley: the take-off and landing machine, home elevator, flag raising, curtain, and rice moving used in the construction site. Movable pulley: hanging people outside the wall, sails, cable cars, cranes, and construction sites during decoration. Pulley block: boom, lift, crane, winch, etc.

A pulley with a fixed shaft is a fixed pulley.

For example, (1) the shaft moves with the pulley is the movable pulley.

For example, (2) the pulley group is assembled together by the fixed pulley and the movable pulley.

Such as (3).

Pulleys are simple machines used to lift heavy loads and save effort.

A pulley is a small wheel with a groove around the perimeter that rotates around an axis. A pulley is a simple machine consisting of a grooved disc that rotates around the central axis and a flexible rope (rope, tape, steel cable, chain, etc.) that can be rotated around the central axis.

In mechanics, a typical pulley is a round wheel that rotates around a central axis. There is a groove on the circumferential surface of the wheel, and the rope is wound around the groove, and either end of the rope is pulled forcefully, and the friction between the rope and the wheel will cause the wheel to rotate around the central axis. A pulley is actually a deformed, rotating lever.

The main function of the pulley is to pull the load, change the direction of force, transmit power and so on.

Machinery that can change the direction of an object or save effort is called a pulley.

There are a lot of drawings about the application of pulleys in the PPT below!!

1) Fixed pulley.

The fixed pulley is essentially an equal-arm lever, which is effortless and effortless, but can change the direction of the force.

Features of fixed pulleys.

It is not labor-saving to pull the hook code through the fixed pulley. With or without a fixed pulley, the spring scale reads the same. It can be seen that the use of fixed pulleys does not save force but can change the direction of force. In many cases, changing the direction of the force will bring convenience to the work.

The principle of fixed pulley.

The fixed pulley is essentially an equal arm lever, and the power L1 and resistance L2 arms are equal to the radius of the pulley. According to the lever balance conditions, it can also be concluded that the fixed pulley is not labor-saving.

2) Movable pulleys.

The movable pulley is essentially a lever that the power arm is twice that of the resistance arm, saving 1 2 force and 1 times more distance.

Features of movable pulleys.

The use of movable pulleys can save half the effort and consume the distance. This is because when using movable pulleys, the hook is suspended by two sections of rope, each of which bears only half the weight of the hook. Although the use of movable pulley saves effort, the distance of power movement is greater than the distance of the hook code elevation, that is, it takes the distance.

The winding of the pulley block should follow the following three principles:

There are two ways to wind the rope of a pulley group, the first is that the rope is tied to the fixed hook of the fixed pulley first, bypasses the moving pulley below, and then bypasses the fixed pulley above; The second is that the rope is first tied to the fixed hook of the movable pulley, bypassing the fixed pulley, and then bypassing the movable pulley, and each pulley rope can only be wound once.

2. Follow the method of even fixed odd motion, if the number of rope segments n is an even number, the fixed end of the rope is on the fixed pulley, if the number of rope segments n is an odd number, the fixed end of the rope is on the movable pulley;

Third, when judging the labor-saving situation of the pulley group, the key is to determine the number of rope segments n that bears the total weight, that is, there are several sections of rope, which are connected to the movable pulley, and the number of rope segments n when the most labor-saving is n=x+1.

The number of rope segments in the physical pulley group can be according to the number of rope segments passing through the fixed pulley and the movable pulley, which can be referred to Figure n below.

The fixed pulley can not save force, and in the case of the rope weight and the standby dismantling and ignition friction between the rope and the wheel are not counted, no matter where the force direction of the protective section of the rope goes, the force used to lift the heavy object is equal, because the power arm and the resistance arm are equal and equal to the radius of the pulley.

The movable pulley saves 1 2 force and takes 1 times more distance, and it is limited to vertical upward force, the greater the angle of force tilting, the more force is used. In addition, the weight of the pulley also has an effect on the force used when using movable pulleys. When the gravity of the pulley is not ignored and the force is applied vertically upwards, we have:

f=(g-wheel + g-matter) 2.