Hobbies And Interests
Pulley Types
The most basic pulley is a single fixed pulley, where the pulley is fixed in a position. In this case, the mechanical advantage is one, meaning the same force is needed with the pulley as without. In a movable pulley system, the pulley is typically attached to the object being moved. The movable pulley has a mechanical advantage of two. In a compound pulley system, a fixed pulley and a movable pulley are combined into one system, creating a mechanical advantage greater than two, but dependent on other factors such as weight, friction and distance.
Moving Heavy Objects
Since a pulley changes the direction of the force on an object, it can make it easier to lift heavy items. The most basic way to demonstrate this would be to have a pulley fixed at a point above the object to be lifted. The rope would attach to the object, thread through the pulley above and reach down to the ground near the object. Pulling on the rope will lift the object; however, the distance lifted is the same as the distance pulled on the rope. For example, pulling the rope 1 m will lift the object 1 m. To improve the mechanical advantage, you can use a compound pulley system. In this case, with a second pulley added to the object, pulling the rope 1 m may lift the object about 3 m.
Sailing
Pulleys serve as important machines on sailing vessels. Commonly called "block and tackle" when used on a sailboat, pulleys are responsible for lifting the large heavy sails into place. Pulley systems are also used in adjusting and tightening the sails, and therefore are integral in the steering and control of the vessel.
Raising an Object
You can use a pulley to raise an object higher than you would normally be able to. A common example of this is a flagpole. The flag is attached to a rope, with a fixed pulley at the top of the flagpole. Window blinds also operate by a fixed pulley system. The user pulls on the string, which is threaded through the pulley, and in turn lifts the blinds.
Moving an Object Laterally
You can use pulleys to move an object from one point to another, without lifting it. The most typical example of this is a clothesline. A clothesline is a two-pulley system, with one on each end of the line. A continuous line is used, so that pulling on it in either direction will cause the items on the line to come closer or to move farther away, depending on which part of the line is pulled.