A hammer is basically a force amplifier that works by converting mechanical work into kinetic energy and back.
A hammer is a tool meant to deliver an impact to an object. The most common uses for hammers are to drive nails, fit parts, forge metal and break apart objects. Hammers are often designed for a specific purpose, and vary in their shape and structure. The term hammer is also used for some devices that are designed to deliver blows, e.g., the caplock mechanism of firearms. The hammer is a basic tool of many professions. The usual features are a handle and a head, with most of the weight in the head. The basic design is hand-operated, but there are also many mechanically operated models, such as steam hammers, for heavier uses.
The use of simple tools dates to about 2,400,000 BCE when various shaped stones were used to strike wood, bone, or other stones to break them apart and shape them. Stones attached to sticks with strips of leather or animal sinew were being used as hammers by about 30,000 BCE during the middle of the Paleolithic Stone Age. The hammer's archeological record shows that it may be the oldest tool for which definite evidence exists of its early existence. Stone hammers that date back to 2,600,000 BCE have been found.
The essential part of a hammer is the head, a compact solid mass that is able to deliver the blow to the intended target without itself deforming. The opposite side may have a ball, as in the ball-peen hammer and the cow hammer. Some upholstery hammers have a magnetized appendage, to pick up tacks. In the hatchet the hammer head is secondary to the cutting edge of the tool.
As the impact between steel hammer heads and the objects being hit can, and does, create sparks, which in some industries such as underground coal mining with methane gas, or in other hazardous environments containing flammable gases and vapours, can be dangerous and risk igniting the gases. In these environments, a variety of non-sparking metal tools are used, being principally, aluminium or beryllium copper-headed hammers.
In recent years the handles have been made of durable plastic or rubber.