Lever

A lever is a length that can hinge about one point, and that point is known as the fulcrum.  Levers have lots of uses, including for weighing things, or for making forces bigger or smaller, or making movements bigger or smaller. All levers feature a fulcrum about which the lever pivots, and depending on the distances from this pivot there will be different amounts of force and of movement. The lever is one of six simple machine. There are three types of levers: first-class, second-class and third-class.

Early
The earliest remaining writings about levers are from the 3rd century BC. They were written by Archimedes. "Give me a place to stand, and I shall move the earth." is a famous quote from Archimedes who stated the correct mathematical principle of levers (quoted by Pappus of Alexandria).

Types of levers
There are three kinds of levers. The difference between them is where the fulcrum is and where the forces are acting.  If the force is nearer the fulcrum, the force will be bigger, but the movement will be less.  If the force is further away from the fulcrum, the force will be smaller, but the movement will be bigger.  Levers can therefore make make forces bigger.  Or make movements more precise.  Or just change the place where a force acts.

First class
A first-class lever is a lever where the fulcrum is in between the effort and resistance (the load). Seesaws and crowbars are examples of first class levers.

Second class
A second-class lever is where the resistance is between the effort and the fulcrum. Wheel barrows and wrenches are examples of second class levers.

Third class
A third class lever is where the effort is between the resistance and the fulcrum. Staplers and your forearm are examples of third class levers.

 References 

Category:Engineering
Category:Tools