Pulley system is very popular and simple machine. It use to change movement direction of cable and can reduce heavy object. A pulley system has a wheel with a groove on an axle or shaft that is designed to support movement , and a rope in the groove.
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I. What are the 3 types of pulleys?
There are three types of pulleys. Each pulley system depends on how the wheel and rope are put together: fixed, movable, and compound.
1. Fixed pulley.
This is the simplest system. The place of the pulley is fixed, the wheel can rotate in axis only, the rope moved in the groove of the pulley.
2. Movable Pulley.
In this case, the object and pulleys can move from place to plate. One end of the rope is attached to a fixed point that does not move.
3. Compound pulley.
It is combined pulleys. In the compound pulley has fixed and movable pulley. It is a combination of pulleys that make the effort less than half of the weight of the load.
II. How does pulley system work?
* Fixed pulley.
+ Using the screws and a screwdriver or drill, to attach the pulley on the place.
+ Through the rope in the groove of the pulley.
+ One end of the rope attach to the object. You can use your hand or machine to pull down on the free end of the rope. When you pull down the rope, the wheel will rotate on the axis and the object will move up.
* Movable Pulley.
+ Using the screws and your screwdriver or drill, attach one fixed pulley on the place.
+ Feed the rope through the pulley, and feed the rope through the movable pulley, and fixed one end the rope on the fix place.
+ Attached the object on the movable pulley.
+ You can use your hand or machine to pull down on the free end of the rope. When you pull down the rope, the wheel will rotate on the axis and the object and movable pulley will move up.
You can see these video below for understanding: How does pulley system work?
III. What is the formula for a pulley system?
For fixed pulley.
As this picture below, we have to move an object with single pulley, and we will calculate the force without friction between the wheel and rope.
M: Mass (kg)
g: acceleration of gravity (m/s²), g = 9.81 m/s²
F: Force to pull the object.(N)
α: angle of the rope.
We can calculate the force as formula: F = Mg/cos(α) = 9.81 M/ cos(α)
For the example, M = 1o kg, α = 60 degree -> F = 10*9.81/cos(60) = 98.1* 2 = 196.2 N
For Movable Pulley and compound pulley.
M: Mass (kg)
g: acceleration of gravity (m/s²), g = 9.81 m/s²
F: Force to pull the object.(N)
n: number of the wheel
We can calculate the force as formula: F = Mg/n = 9.81M/n
For the example, M = 1o kg, n=2 -> F = 10*9.81/2 = 98.1/ 2 = 49.05 N
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