We generally think of machines as a complex system. A hammer, a screw driver, handle of a fridge, a steering wheel of a car – all these can also be called as simple machines because any device that helps accomplish a work can be called machine. There are many complex machines like an engine etc but these are actually combination of many simple machines.
Machines perform work in many ways – they either transform energy from one form to another or multiply force/speed in order to complete the desired task. For example, a generator is a machine that converts mechanical energy into electrical energy. One good example of a machine that multiplies force is the pulley system that lifts weights and that which multiplies speed is the bicycle.
Once the working principle of simple machines is understood, it becomes easier to understand the working of complex machines. Therefore on the basis of their working principle, physicists classify all the simple machines as either ‘levers’ or ‘inclined plane’.
A lever is basically a simple machine used to lift heavy loads. An inclined plane helps raise or lower heavy weights over a long distance with the application of a small force. One common example of lever is the ‘see saw’ we see in the park and that of inclined plane is the ‘ramp’.