Simple machines are basic mechanical devices that are used to make work easier. There are six types of simple machines:

1. Lever: A rigid bar that pivots around a fixed point called a fulcrum. The three types of levers are first class, second class, and third class.

2. Pulley: A wheel with a groove around its circumference that is used to change the direction of a force.

3. Wheel and axle: A wheel with a rod (axle) through its center that is used to transmit force.

4. Inclined plane: A sloping surface used to raise or lower a load.

5. Wedge: A simple machine that is an inclined plane with one or two sloping sides used to separate or lift objects.

6. Screw: A simple machine that is an inclined plane wrapped around a cylinder or cone used to hold objects together or lift them.