"Pulley" Mechanical and Work PPT Courseware 3

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"Pulley" Mechanical and Work PPT Courseware 3

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Group work: Use a rope and a pulley to lift goods to a high place. What method do you have?

Please use hook codes instead of heavy objects to simulate.

Experiment: Study the characteristics of the force, direction and moving distance when using fixed pulleys or movable pulleys to lift objects.

Wrap a strip of white paper around the vertical pole of the iron stand, and draw four or five red lines at equal distances on the paper. In this way, the distance the weight rises and the distance the free end of the rope moves can directly find out the multiple relationship or read the grid. Number, the same is true when studying pulley blocks. The hook code should be as large as possible and the pulley mass should be as small as possible.

Using a fixed pulley is neither labor-saving nor labor-intensive, but it can change the direction of the force. s=h, F=G．

Using a movable pulley can save half the force, but it takes twice the distance and does not change the direction of the force. S=2h, F=G/2．

Although the fixed pulley can change the direction of force and make our work convenient, it cannot save labor;

Although the movable pulley can save half the force, it cannot change the direction of the force, which often makes it inconvenient to use.

So people used fixed pulleys and movable pulleys in combination, combining their respective advantages to form a pulley block.

A. Explore the winding method of a pulley block composed of a fixed pulley and a movable pulley;

B． Explore the labor saving and moving distance of a pulley block consisting of a fixed pulley and a movable pulley.

a. Two sections of rope are wound to bear the weight, and the relationship between the distance s moved by the power application point (rope end) and the distance h raised by the weight is measured from the equidistant red line grid on the vertical pole of the iron platform.

Conclusion: It can be seen that F = G/2, s = 2 h.

b. Wind up three sections of rope to bear the weight, and use a spring dynamometer to pull the force. Pull the spring dynamometer vertically upward to measure the force. The two distances are still measured by the equidistant red lines on the vertical poles of the iron platform. ．

Conclusion: It can be seen that F=G/3, s=3h.

Section 3 Pulley

1. Fixed pulley:

(1) Usage features: It can change the direction of force without saving effort or effort; without saving distance or distance.

(2) Essence: It is an equal-arm lever.

2. Moving pulley:

(1) Usage characteristics: It can save half the force, but does not change the direction of the force; it can move twice as far.

(2) Essence: The power arm is twice the lever of the resistance arm.

3． pulley block

(1) Advantages of use: It can save effort and change the direction of force; but it cannot save both effort and distance.

(2) Formula: F = G total / n = (G object + G moving pulley) / n (excluding pulley friction)

s=nh

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Update Time: 2024-10-24

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