The lever was first described in 260 B.C.E. by Archimedes(c.287-212 B.C.E.),but probably came in to play in prehistoric times.A lever can be used to raise a weight or overcome resistance.it consists of a bar,pivoted bat a fixed point known as the fulcrum.Extra power can be gained for the same effort if the position of the fulcrum is changed.
Levers may be divided in to classes.First-class levers have the fulcrum in between the applied force and load,which are at opposite ends,such as with the seesaw.Second-class levers have the fulcrum at one end,and the applied force at the other,such as with a bottle opener.Finally,third -class levers have the effort in between the fulcrum and the load;for example,tweezers have two class three levers that are pressed together to do the work for which they are designed.
The Egyptians used a lever in 5000 B.C.E. for weighing,pivoting a bar at its center to balance weights and the objects to be weighed.Ramps and levers were also used to move stones higher up a structure,adapting the principle of the shaduf,which was developed in Egypt in 1500 B.C.E.This machine had a lever pivoted near one end with a water container hanging from the short arm and counterweights attached to the long arm.Several times a person's weight could be lifted by pulling down the long arm.