Who can tell me all about pulleys?

1. Precautions when assembling the pulley block

① Determine how many rope sections of the pulley block bear the total weight, and analyze the parity of the number of sections. If the number of sections is an odd number, then the fixed end of the rope must be tied On the moving pulley. If the number of segments of the rope carrying the load is an even number, then the fixed end of the rope must be tied to the fixed pulley, that is, odd-moving and even-fixed.

② Determine the number of fixed pulleys and movable pulleys based on the number of rope segments that bear the total weight. The specific situation is as follows:

(Note: Since the number of rope segments can only be integers, the n value can only be rounded up and not rounded)

Example 1. Excluding the weight of the pulley set, use 200N to lift How many pulleys should be used for a 900N weight? How to install? (The direction of the pulling force is required to be downward)

Analysis: According to the law of effort saving of the pulley block F=(1/n)G, find n. Then determine the number of pulleys based on the principle of "must match one move" combined with the n solution. Finally, according to the parity of n, it is determined that the fixed end of the rope is tied to the fixed or movable pulley.

Solution: Because F=(1/n)G; so n=4.5 paragraphs

Suppose n=5 is an odd number. According to the odd-even-even principle, the fixed end of the rope is tied to On the movable pulley, four pulleys are required, namely two fixed pulleys and two movable pulleys.

Because the direction of the pulling force needs to be changed, and according to the principle of "change direction plus constant", an additional fixed pulley must be added, that is, three fixed pulleys, and the two movable pulleys are installed as shown in Figure 1.