Simple Machines

 A simple machine is "any of the basic mechanical devices for applying force"  Simple machines were made to make work easier. There are 6 main machines also known as the "six simple machines", which are the wheel and axle, the lever, the inclined plane, the pulley, the screw and the wedge. 

Wheel and Axle

According to livescience the wheel is one of the most significant inventions in the history of the world. the wheel was invented in 3500 B.C., it was created to make transportation easier by reducing friction when it being rolled over an object. Also when mounting the wheel on the axle led to the development of wagons, chariots and carts.

Lever

The Lever was created by Archimedes, he realized "that in order to accomplish the same amount or

work, one could make a trade-off between force and distance using a lever" Most levers have a long beam and a pivot, the lever depends on the ratio of weight on each side of the beam, kinda like a seesaw.  

Inclined Plane

An inclined plane is like a ramp, just a surface raised at an angle to help lift an object. The inclined plane allows someone to lift a load that would be to heavy to lift straight up, which make the time a lot longer but the effort needed to raise the object is decreased. Like the Egyptians used to make there pyramids, instead of lifting blocks straight up they would make ramps. 

Pulley

A pulley system like the inclined plane is a trade for increased distance for decreased force. If 

someone was to lift and wight with a rope, the pulley would be attached to a beam. The pulley would

allow you to pull down other than up. now lets say if there was 2 pulleys then 

the rope would go though the pulley on the weight and the one on the beam 

and they would only have to pull half of the weight but double the distance.   

 Screw 

"A screw is essentially a long incline plane wrapped around a shaft, so its mechanical advantage can be approached in the same way as the incline," according to HyperPhysics, 

Wedge 

Wedges are driven under something to lift and into something to split. Longer, skinnier wedges are

better to use than fatter wedges because in gives more of a Mechanical advantage ("the ratio of the force produced by a machine to the force applied to it, used in assessing the performance of a machine".)

http://www.livescience.com/49106-simple-machines.html