Types of pulleys
There are 3 main types of pulleys. The fixed Pulley, the movable pulley, an the block and tackle
How does a fixed pulley work?
The Fixed pulley is used for changing the direction of the input force, these pulleys would be used for flagpoles or with a hoisting device, the pulley is usually attached to a stationary object above the load. When the rope is pulled downward, the effect is that the load is lifted upwards, this type of pulley will not reduce the effort needed to lift the load, but using the force of gravity and your weight in your favor. The mechanical advantage is 1, and to lift the load a foot, you will have to pull a foot of rope downward.
How does a movable pulley work?
The movable pulley is used to reduce the amount of input force to lift a load. The most popular system that uses this pulley would be a well. Unlike the fixed pulley, the movable pulley is attached to the load, and is lifted by pulling up on the rope, making it twice as easier to lift a heavy object. In this case, a 20 pound load could be lifted with just 10 pounds of input force. The tradeoff is that you would have to pull twice the amount of rope, and gravity is not in your favor by pulling off.
How does a block and tackle pulley work?
The block and tackle uses one fixed and one movable pulley to reduce the amount of force needed to lift the object by however many pulleys are incorporated into the system. The trade off is that you will have to pull however many times more rope to lift the object. The mechanical advantage decides how much rope would be needed to pull the object a certain distance and how much force would be needed to move the object.
For example in the picture above the mechanical advantage is 3 because there is the fixed pulley with a mechanical advantage of 1, and a movable pulley with a mechanical advantage of 2, added together they make the mechanical advantage of 3, both pulleys even out the amount of force, the tradeoff is that you would have to pull 3 feet of rope to lift the object a foot.