A device that can change the route and size of a force is called a Machine. In very simply words we can say that the use of mechanical advantage to increase force. A simple machine exploits a single functional force to undertake a work against a single load force. Ignoring resistance fatalities, work done on the load is equal to the work done by the concerned force. This is used to increase the force productivity, at the cost of relative decline in the distance covered by the load. Mechanical advantage is the ration of output to the input force. We can do various works with the help of simple machine like increasing the speed of force, changing the direction of force, increasing input force etc.
Renaissance scientists defined six classical simple machines:
Lever
Wheel and axle.
Pulley.
Inclined Plane.
Wedge.
Screw.
These are the basic "building blocks" of almost all complex machines that also called "compound machines" e.g. wheel, pulleys, lever are used in bicycle.
Simple machine can be more classified into two categories, one those reliant on vector resolution of force including screw wedge etc and other are those which contains equilibrium of torques like lever, wheel etc.
This idea of a Simple Machine was initiated with the Greek philosopher Archimedes nearly the 3rd century BC. He studied "Archimedean" about simpler machines like lever, pulley and screw. The principle of mechanical advantage was discovered by him.
All machine works in a different way, but the function is alike mathematically. In every machine a force is provided to the device through one point and machine moves the load at another point. Even though some machines used only to segregate the position of force. Mostly machines are used to multiply or divide the size of force by mechanical advantage, which can be evaluated through machine's geometry.
Simple machines can not do more work than receiving input force as they don't have a source of energy. If attention is not paying to friction and elasticity the output is equal to input.
