What is the principle of a simple machine?

Machines simply transmit mechanical work from one part of a device to another part. A machine produces force and controls the direction and the motion of force, but it cannot create energy. A machine's ability to do work is measured by two factors. 

1) Mechanical advantage: In machines that transfer only mechanical energy, the ratio of the force exerted by the machine to the force applied to the machine is known as mechanical advantage. In this mechanical advantage, the distance the load will be moved will only be a fraction of the distance through which the effort is applied. 

2) Efficiency: The efficiency of a machine is the ratio between the work it supplies and the work put into it. Although friction can be decreased by oiling any sliding or rotating parts, all machines produce some friction.