Editing Hammer (section)

==Physics==

===As a force amplifier===
A hammer is a simple [[force]] [[amplifier]] that works by converting [[mechanical work]] into [[kinetic energy]] and back.

In the swing that precedes each blow, the hammer head stores a certain amount of kinetic energy—equal to the length ''D'' of the swing times the force ''f'' produced by the [[muscle]]s of the arm and by [[gravity]]. When the hammer strikes, the head is stopped by an opposite force coming from the target, equal and opposite to the force applied by the head to the target. If the target is a hard and heavy object, or if it is resting on some sort of [[anvil]], the head can travel only a very short distance ''d'' before stopping. Since the stopping force ''F'' times that distance must be equal to the head's kinetic energy, it follows that ''F'' is much greater than the original driving force ''f''—roughly, by a factor ''D''/''d''. In this way, great strength is not needed to produce a force strong enough to bend steel, or crack the hardest stone.

===Effect of the head's mass===
The amount of energy delivered to the target by the hammer-blow is equivalent to one half the mass of the head times the square of the head's speed at the time of impact <math>(E={mv^2 \over 2})</math>. While the energy delivered to the target increases linearly with mass, it increases quadratically with the [[speed]] (see the effect of the handle, below). High tech [[titanium]] heads are lighter and allow for longer handles, thus increasing velocity and delivering the same energy with less arm fatigue than that of a heavier steel head hammer.<ref>{{cite web |title=DeWalt's Titanium Hammer Killer? |url=http://toolmonger.com/2011/06/15/dewalts-titanium-hammer-killer/ |date=2011-06-15 |author=Cage, Chuck |publisher=Toolmonger |access-date=2013-04-18}}</ref> A titanium head has about 3% [[Deflection (physics)|recoil]] energy and can result in greater efficiency and less fatigue when compared to a steel head with up to 30% recoil. [[Dead blow hammer]]s use special rubber or steel shot to absorb [[recoil]] energy, rather than bouncing the hammer head after impact.

===Effect of the handle===
The handle of the hammer helps in several ways. It keeps the user's hands away from the point of impact. It provides a broad area that is better-suited for gripping by the hand. Most importantly, it allows the user to maximize the speed of the head on each blow. The primary constraint on additional handle length is the lack of space to swing the hammer. This is why sledgehammers, largely used in open spaces, can have handles that are much longer than a standard carpenter's hammer. The second most important constraint is more subtle. Even without considering the effects of fatigue, the longer the handle, the harder it is to guide the head of the hammer to its target at full speed.

Most designs are a compromise between practicality and [[Efficient energy use|energy efficiency]]. With too long a handle, the hammer is inefficient because it delivers force to the wrong place, off-target. With too short a handle, the hammer is inefficient because it does not deliver enough force, requiring more blows to complete a given task. Modifications have also been made with respect to the effect of the hammer on the user. Handles made of shock-absorbing materials or varying angles attempt to make it easier for the user to continue to wield this age-old device, even as nail guns and other powered drivers encroach on its traditional field of use.

As hammers must be used in many circumstances, where the position of the person using them cannot be taken for granted, trade-offs are made for the sake of practicality. In areas where one has plenty of room, a long handle with a heavy head (like a sledgehammer) can deliver the maximum amount of energy to the target. It is not practical to use such a large hammer for all tasks, however, and thus the overall design has been modified repeatedly to achieve the optimum utility in a wide variety of situations.

===Effect of gravity===
[[Gravity]] exerts a force on the hammer head. If hammering downwards, gravity increases the [[acceleration]] during the hammer stroke and increases the [[energy]] delivered with each blow. If hammering upwards, gravity reduces the acceleration during the hammer stroke and therefore reduces the energy delivered with each blow. Some hammering methods, such as traditional mechanical [[pile driver]]s, rely entirely on gravity for acceleration on the down stroke.