Is there a problem with levers and pulleys?

The fixed pulley is essentially an equal-arm lever, which is effortless and effortless, but can change the direction of the force. The power arm and resistance arm of the lever are respectively the radius of the pulley, and since the radius is equal, the power arm is equal to the resistance arm, and the lever is neither labor-saving nor labor-intensive.

The fixed pulley can not save force, and in the case of rope weight and the friction between the rope and the wheel are not counted, the force used to lift the heavy object is equal no matter where the force direction of the rope goes, 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 costs 1 times more distance, this is because when using the movable pulley, the hook code is suspended by two sections of rope, and each section of rope only bears half of the weight of the hook code, and the direction of the force cannot be changed. In essence, it is a lever that is twice the power arm (L1) and the resistance arm (L2).

The pulley is the lever with the fulcrum in the middle of the wheel, but it is actually said to be a lever only because it conforms to the law of leverage.

Its power arm and resistance arm are all radius, naturally a so-called equal arm lever, the same as the pulley is used normally (vertical pull-up), the fulcrum is the tangent point of the line hanging on the wall and the wheel, and the power arm is twice the radius.

The resistance arm is the radius, so half of the force is saved.

Both are simple machines, with the advantages of saving effort and changing the direction of force, and the essence of both is the same; The difference is that the pulley can continuously change the direction and magnitude of the force, while the lever can only move a certain distance and direction.

The fixed pulley is an equal-arm lever that does not save distance and does not save force to change the direction of force.

The movable pulley is a labor-saving lever that saves effort and costs distance without changing the direction of the force.

The pulley block saves effort and changes the direction of force.

leverage, which adds borrowed currency to existing funds for investment; Leverage, the ratio of assets to bank capital. The rational use of the principle of leverage is helpful for enterprises and individuals to accelerate their development and improve efficiency, but there is also a risk that they cannot be repaid when due.

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.

Summary of lever and pulley knowledge pointsLi Weizhi's studio lever pulley knowledge point summary.

1 Lever: A hard rod that can rotate around a fixed point under the action of force is called a lever.

2 What is Fulcrum, Power, Resistance, Power Arm, Resistance Arm?

1) Fulcrum: The point (o) around which the lever turns

2) Power: The force (f1) that makes the lever turn

3) Resistance: The force (f2) that prevents the lever from turning

4) Power arm: the distance (L1) from the fulcrum to the line of action of the power.

5) Resistance arm: the distance (L2) from the fulcrum to the resistance line

3 Conditions for Lever Balance: Power Power Arm = Resistance Resistance Arm. or write: f1l1=f2l2 or write . This equilibrium condition is also known as the lever principle discovered by Archimedes.

4 Three Leverages:

1) Labor-saving lever: L1>L2, F1F2 when balanced. It is characterized by laborious, but saves distance. (such as fishing rods, barber scissors, etc.).

3) Equal arm lever: L1=L2, F1=F2 when balanced. It is characterized by neither effortless nor labor. (e.g. balances).

5. Characteristics of fixed pulley: it is not labor-saving, but it can change the direction of power. (Essentially an equiarm lever).

6. Characteristics of movable pulley: save half of the force, but can not change the direction of power, and it costs distance. (The essence is that the power arm is twice the lever of the resistance arm).

7 Pulley: When using a pulley, the pulley block uses several sections of rope to hang the object, and the force used to lift the object is a fraction of the weight of the object.

8 Actual pulley block: mechanical efficiency = w useful work w total work = gh fs = g nf, n is the number of rope sections that bear the weight.

9 Pulley block ignoring rope weight and friction: g object * h (g object * h + g motion * h) = g (g + g motion), tensile force: f = (g + g motion) n

The pulley is a deformation of the bar compound rod, which is controlled by the lever machinery.

The fixed pulley is essentially a lever of the same arm, which is neither labor-saving nor effortless, but can be used to change the direction of the force. The power arm and resistance arm of the lever DAO are the radius of the pulley, and since the radius is equal, the power arm is equal to the resistance arm, and the lever is neither labor-saving nor labor-intensive.

The movable pulley saves 1 2 force and costs 1 times more distance, this is because when using the movable pulley, the hook code is suspended by two sections of rope, and each section of rope only bears half of the weight of the hook code, and the direction of the force cannot be changed. In essence, it is a lever that is twice the power arm (L1) and the resistance arm (L2).

That's right! copy

A pulley is a small wheel with a groove around the perimeter that rotates around an axis.

A pulley is a simple machine that can rotate around a central axis consisting of a grooved disc that rotates around the central axis and a flexible rope (rope, tape, steel cable, chain, etc.) that crosses the disc. 】

The pulley is a deformation lever, which belongs to the simple machinery of the lever class and has a wide range of uses. In my country, as early as the Warring States Period, there is a record of pulleys in the book "Ink Classic". The pulley with a fixed central shaft is called a fixed pulley, which is a deformed equal-arm lever that is effortless and effortless but can change the direction of the force.

The pulley whose central shaft moves with the weight is called the moving pulley, which is a deformed unequal arm lever (labor-saving lever), which can save half the force, but costs twice the distance (the movable pulley rises n meters, the free end of the string rises 2n meters, n 0), and cannot change the direction of the force. No matter where the force direction of the fixed pulley rope goes, the force used to lift the heavy object is equal (the power arm and the resistance arm are equal and equal to the radius of the pulley); When the movable pulley rope is stressed vertically upward, it is the most labor-saving.

In practice, a certain number of movable pulleys and fixed pulleys are often combined into various forms of pulley groups. The pulley block saves effort and can change the direction of the force. The differential pulley (commonly known as chain hoist) commonly used in the factory is also a pulley block.

Pulley blocks are widely used in cranes, winches, lifts and other machinery. The pulley has appeared in the form of knowledge points in books such as the sixth grade of science in the People's Education Edition and the eighth grade of Shanghai Education (all one volume), requiring the distinction of labor-saving, changing direction, and drawing pulley groups.

There are many examples of pulleys and levers in life.

For example, the fixed pulley: the flagpole of the flag-raising is the fixed pulley; A lot of fitness equipment used in the gym is also a fixed pulley, you can observe it when you have time, this is the most obvious application of the fixed pulley, because the fixed pulley can change the direction of the force, but it does not save effort, does not save distance, and can meet the requirements of fitness.

Movable pulleys: tower cranes on construction sites; Movable pulleys are also used for the retraction and lowering of the sails. Because the movable pulley can save half the force, but it takes a general distance and does not change the direction of the force.

The crane uses a fixed mix wheel and a lever, and the pliers are the levers

The movable pulley is a labor-saving lever.

The pulley in which the position of the shaft moves with the object being pulled is called a movable pulley. The movable pulley is essentially a lever (labor-saving lever) in which the power arm is equal to 2 times the resistance arm. It cannot change the direction of the force, but it can save up to half of the force, but it does not save work.

It can form a pulley group with a fixed pulley. It is a simple machine commonly used in daily life.

Definition. When used, a pulley in which the shaft moves with the object is called a movable pulley. The movable pulley can be regarded as a labor-saving lever, o is the fulcrum of the lever, and the shaft of the pulley is the point of action of the resistance. The force exerted by the lifted object on the shaft is the resistance, and the force exerted by the rope on the wheel is the driving force.

When lifting a heavy load, if the ropes on both sides are parallel, the power arm is twice as long as the resistance arm; When the movable pulley is balanced, the power is half of the resistance. Therefore, if the gravity of the moving pulley itself is not counted, the use of the movable pulley can save half of the force, but at this time, the direction of the force cannot be changed, and the rope can be pulled upward to lift the heavy object.

Definition 1: A pulley in which the position of the shaft moves with the object being pulled is called a movable pulley.

Definition 2: If the direct elimination base of the heavy object is hung on the pulley, and the pulley also rises together when the heavy object is lifted, such a pulley is called a moving pulley.

Definition 3: If a person stands on the pulled object and pulls the rope, the pulley moving relative to the ground is equivalent to a fixed pulley, and the fixed one is a movable pulley, so the definition of a movable pulley is a movable pulley relative to the person who applies force If the pulley moves, it is a movable pulley, otherwise it is a fixed pulley.

Peculiarity. 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 pulleys saves the high force of the base bridge, the distance of the power movement is twice the distance of the hook raised, that is, the distance.

The direction of the force cannot be changed. Moves as the object moves. In addition, the quality of the movable pulley itself cannot be ignored in life, so extra work is done in the process of the movable pulley rising to reduce the mechanical efficiency.

Definition: A pulley that moves with a heavy object. (It can be moved up and down the ruler, or left and right).

Substance: The power arm is a labor-saving lever that is twice that of the resistance arm.

Features: The use of movable pulleys can save half of the force, but it cannot change the direction of power.

Ideal movable pulley (regardless of inter-shaft friction and movable pulley gravity).

Summary. Using a lever or pulley can lift an object by changing the mode of action of the force. The exact effect depends on the design of the lever or pulley and how it is used.

1.Use a lever to lift an object: The principle of a lever is to use the relationship between the fulcrum and the force arm to increase the force.

When an object is placed on a fixed fulcrum and then a smaller force is applied at a distance from the fulcrum, the smaller force can be converted into a larger force by the lever principle. In this way, less force is required to lift the object, but more distance is required. 2.

Use pulleys to lift objects: The pulley principle is to use the rope or chain on the pulley to share the gravity of the object and change the direction of the force. By increasing the number of pulleys, the required force can be further reduced.

For example, if a system of multiple pulleys is used, each pulley will reduce the amount of force and thus the force required to lift the object. In this way, less force is required to lift the object, but it also requires more travel distance. The principle of lifting an object with a lever or pulley is to reduce the force required by changing the magnitude or direction of the force, thus making it easier for people to complete the lifting of the object.

Through reasonable design and use, physical principles can be used more efficiently to complete the work and reduce people's labor intensity.

Using a lever or pulley can lift an object by changing the mode of action of the force. The exact effect depends on the design of the lever or pulley and how it is used. 1.

Use a lever to lift an object: The principle of a lever is to use the relationship between the fulcrum and the force arm to increase the force. When an object is placed on a fixed fulcrum and then a smaller force is applied at a distance from the fulcrum, the smaller force can be converted into a larger force by the lever principle.

In this way, less force is required to lift the object, but more distance is required. 2.Use the pulley to lift the object:

The pulley principle is to use the rope or chain on the pulley to share the gravity of the object and change the direction of the force. By increasing the number of pulleys, the required force can be further reduced. For example, if a system of multiple pulleys is used, each pulley will reduce the amount of force and thus the force required to lift the object.

In this way, the force required to lift the object is reduced, but it also requires a greater distance to be lifted. The principle of lifting an object with a lever or pulley is to reduce the force required by changing the magnitude or direction of the force, thus making it easier for people to complete the lifting of the object. Through reasonable design and use of macros, physical principles can be used more efficiently to complete the work, and reduce people's labor intensity.

(1) The fixed pulley is essentially a lever, and the power arm and the resistance arm are the radius of the pulley, so they belong to the equal arm lever (2) The movable pulley is essentially a labor-saving lever, because the power arm is the diameter of the pulley, and the resistance arm is its radius The power arm is 2 times that of the resistance arm (3) According to the lever balance condition: f1 l1 = f2 l2 It can be seen that it saves half the force (4) The force direction of the movable pulley is the same as the direction of the object movement.

Therefore, the answer to this question is: equal arm 2 times half the direction of force.