Those tools or devices which make our work easier and convenient in the direction of force is called simple machine.
Simple machine helps us by magnifying force, accelerating work and by changing the direction of force.
Velocity ratio of simple machine is the ratio of distance traveled by effort to the distance traveled by load in the machine.
The efficiency of a simple machine is defined as the ratio of useful work done by machine (output work) to the total work put into machine (input work).
The ratio of the load to the effort in a simple machine is called mechanical advantages or actual advantage of the machine.