Claw hammer: Hammer pulling nail
Claw hammer is used as a lever to pull a nail from a wood board. When the handle is pulled with a certain force (shorter arrow), the claw pulls the nail with a greater force (longer arrow). Here the ratio of the two forces is about 3.5.
When we do any work, force has to be applied. A force has to be used efficiently so that maximum work is done. For example, if a large load has to be lifted, then a large force has to be applied. Such a large force may not be available. Then how will you lift a large load? It is here where simple machines come into the picture.
It is possible to magnify applied force with the use of simple machines. Simple machines perform work in such a way that the force applied is used efficiently and usefully.
Simple machine is a device through which an applied force at a point is transmitted to another point with a convenient change of magnitude and if required direction also.
Without any conscious thoughts, we are always employing simple machines to make our lives better. Don't we use a fork to lift food from our plate, a pair of scissors to cut a cloth or a hinge to open a door? These are nothing but simple machines. Early man also employed some simple machines: used stone axe to cut or a long stick to shift a boulder. Archimedes is credited with the invention of the screw and the lever. Archimedes lived in Greece around the 250 B.C. He even pronounced, "Give me a place to stand and a long stick, I will lift the earth."
It is interesting to note that many of the parts of human or animal bodies function on the principle of levers. Jaws and elbows represent simple machines, too.
Thus a machine is a tool used to make work easier. Simple machines are simple tools used to make work easier. Compound machines have two or more simple machines working together to make work easier.