When you think of pulleys you picture an assortment of pulleys and ropes working in sync to move large objects. You might think there is only one type of pulley and it just comes in different sizes depending on the need. That is a misconception. Variety does lie in their size, but there are only three main types of pulleys.
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A Pulleys Function
Consisting of a wheel with a groove around its outer edge (for the rope) and an axle, with the assistance of ropes, chains or cords a pulley makes moving objects upward easier. The direction of the force needed to lift an object is changed from pushing up to pulling down when you use a pulley system. Each designed to make your work load more manageable, pulleys are classified as one of three types: movable, fixed or combined.
A Movable Pulley
As the name implies this pulley moves with the object you are lifting. The dynamics of this type of pulley means it requires less effort than the weight of the load to lift it. An example of this would be when you have a twenty pound object that you need to lift upward, it would only need ten pounds of effort to lift it when using a pulley. This pulley's disadvantage is the pulley itself has to be pushed up or down.
A Fixed Pulley
When a pulley is attached or fixed in place to an immovable spot such as a wall or ceiling it is known as a fixed pulley. The positioning of the pulley acts more like a lever and does not decrease the effort needed to lift the object. Its main advantage is you will not have to move the pulley up or down for it to function.
A Combined Pulley
By using a combination of fixed and movable pulleys you will have created a combined pulley. This arrangement of pulleys reduces the effort needed to lift your object by less than half of its weight. The disadvantage is that you will need more space (or distance) for it to operate as the rope or chain is of greater length. You may have heard combined pulleys referred to by their other common name of block and tackle.
Pulleys You Never Thought Of
Though commonly used as a working part of construction cranes or lifting loads on ships, pulleys are a part of your everyday life too. Did you realize that pulleys are at work on flag poles and window blinds, in elevator mechanisms and the window washers lift, the fan belt and water pump in your car, and the conveyor belt at the checkout counter where you shop? Without realizing it pulleys are all around you making your life a little easier.