Answer:
The lever, the pulley, and the inclined plane are three simple machines. Other machines are either modifications of one of those machines or combinations of two or more of them. There are two kinds of pulleys-the fixed and movable. The fixed pulley is the one with immovable axis. There is no mechanical advantage in such pulley. However, the movable pulley is one with axis free to move. It is dependent on the number of ropes. The wheel and axle is really a development of a lever;it is a sort of lever revolving around a fulcrum. It consists of a wheel to which is attached a much smaller wheel. The screw is one of the most powerful machines known and it is an inclined plane.
