Short Notes:

A pulley consists of a chain or a belt passed around a wheel or a series of wheels. Like the lever, a pulley can reduce the effort needed to raise an object, but a pulley can also redirect the applied force. Such an advantage comes at a cost: The smaller the effort needed to lift a weight, the longer the distance through which the effort must move. A combination of pulleys multiplies the advantage by the number of weight-bearing chains used, according to the simple equation F = (1/n)W where F is the force needed to move the object, n the number of weight-bearing chains, and W the weight of the object.

These effort-saving devices serve many purposes, ranging from hoisting massive stell beams at building sites to raising flags.