A hammer is a lever, one of the six types of simple machines. A lever is defined as any rigid bar that pivots around a fixed point, called a fulcrum, to apply force.
A claw hammer can have two possible fulcrums, depending on how it is used. When driving a nail, the fulcrum is wherever the user holds the handle. If using the hammer to pull the nail back out again, the fulcrum becomes the point where the top of the hammer rests against the surface holding the nail. Other common household levers include crowbars, hoes, scissors and bottle openers.