Ahammer is atool, most often ahand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drivenails intowood, to shapemetal (as with aforge), or to crushrock.[1][2] Hammers are used for a wide range of driving, shaping, breaking and non-destructive striking applications. Traditional disciplines includecarpentry,blacksmithing,warfare, andpercussive musicianship (as with agong).
Hammering is use of a hammer in its strike capacity, as opposed toprying with a secondary claw orgrappling with a secondary hook. Carpentry and blacksmithing hammers are generally wielded from a stationary stance against a stationary target as gripped and propelled with onearm, in a lengthy downwardplanar arc—downward to addkinetic energy to the impact—pivoting mainly around the shoulder and elbow, with a small but brisk wrist rotation shortly before impact; for extreme impact, concurrent motions of thetorso and knee can lower the shoulder joint during the swing to further increase the length of the swing arc (but this is tiring). War hammers are often wielded in non-vertical planes of motion, with a far greater share of energy input provided from the legs and hips, which can also include a lunging motion, especially against moving targets. Small mallets can be swung from the wrists in a smaller motion permitting a much higher cadence of repeated strikes. Use of hammers and heavy mallets fordemolition must adapt the hammer stroke to the location and orientation of the target, which can necessitate aclubbing orgolfing motion with a two-handed grip.
The modern hammer head is typically made ofsteel which has beenheat treated for hardness, and the handle (also known as ahaft orhelve) is typically made of wood orplastic.
Ubiquitous inframing, theclaw hammer has a "claw" to pull nails out of wood, and is commonly found in an inventory of household tools inNorth America. Other types of hammers vary in shape, size, and structure, depending on their purposes. Hammers used in manytrades includesledgehammers,mallets, andball-peen hammers. Although most hammers are hand tools,powered hammers, such assteam hammers andtrip hammers, are used to deliverforces beyond the capacity of the human arm. There are over 40 different types of hammers that have many different types of uses.[3]
For hand hammers, the grip of the shaft is an important consideration. Many forms of hammering by hand are heavy work, andperspiration can lead to slippage from the hand, turning a hammer into a dangerous or destructive uncontrolled projectile. Steel is highlyelastic and transmitsshock andvibration; steel is also a good conductor of heat, making it unsuitable for contact with bare skin in frigid conditions. Modern hammers with steel shafts are almost invariably clad with a synthetic polymer to improve grip,dampen vibration, and to providethermal insulation. A suitably contoured handle is also an important aid in providing a secure grip during heavy use. Traditional wooden handles were reasonably good in all regards, but lack strength and durability compared to steel, and there are safety issues with wooden handles if the head becomes loose on the shaft.
The high elasticity of the steel head is important in energy transfer, especially when used in conjunction with an equally elasticanvil.
In terms ofhuman physiology, many uses of the hammer involve coordinatedballistic movements under intense muscular forces which must be planned in advance at theneuromuscular level, as they occur too rapidly for conscious adjustment in flight. For this reason, accurate striking at speed requires more practice than a tapping movement to the same target area. It has been suggested that the cognitive demands for pre-planning, sequencing and accurate timing associated with the related ballistic movements ofthrowing, clubbing, and hammering precipitated aspects ofbrain evolution in earlyhominids.[4]
History
The use of simple hammers dates to around 3.3 million years ago according to the 2012 find made bySonia Harmand and Jason Lewis ofStony Brook University, who while excavating a site nearKenya'sLake Turkana discovered a very large deposit of various shaped stones including those used to strikewood,bone, or other stones to break them apart and shape them.[5][6] The first hammers were made without handles. Stones attached to sticks with strips ofleather oranimal sinew were being used as hammers with handles by about 30,000 BCE during the middle of thePaleolithic Stone Age. The addition of a handle gave the user better control and less accidents. The hammer became the primary tool used for building, food, and protection.[7]
The hammer's archaeological record shows that it may be the oldest tool for which definite evidence exists.[5][6]
A traditional hand-held hammer consists of a separate head and a handle, which can be fastened together by means of a specialwedge made for the purpose, or byglue, or both. This two-piece design is often used to combine a dense metallic striking head with a non-metallic mechanical-shock-absorbing handle (to reduceuser fatigue from repeated strikes). If wood is used for the handle, it is oftenhickory orash, which are tough and long-lasting materials that can dissipateshock waves from the hammer head.[2] Rigidfiberglass resin may be used for the handle; this material does not absorb water or decay but does not dissipate shock as well as wood.
A loose hammer head is considered hazardous due to the risk of the head becoming detached from the handle while being swung becoming a dangerous uncontrolled projectile. Wooden handles can often be replaced when worn or damaged; specialized kits are available covering a range of handle sizes and designs, plus special wedges and spacers for secure attachment.
Some hammers are one-piece designs made mostly of a single material. A one-piece metallic hammer may optionally have its handle coated or wrapped in aresilient material such asrubber for improved grip and to reduce user fatigue.[8]
The hammer head may be surfaced with a variety of materials includingbrass,bronze, wood, plastic, rubber, or leather. Some hammers have interchangeable striking surfaces, which can be selected as needed or replaced when worn out.
Designs and variations
The parts of a hammer are theface,head (includes thebell andneck, which are not labeled),eye (where thehandle fits into),peen (also spelled pein and pane). The side of a hammer is thecheek and some hammers havestraps that extend down the handle for strength. Shown here are: A. Ball-peen hammer B. Straight-peen hammer C. Cross-peen hammerThe claw of a carpenter's hammer is frequently used to remove nails.
A large hammer-like tool is amaul (sometimes called a "beetle"), a wood- or rubber-headed hammer is amallet, and a hammer-like tool with a cutting blade is usually called ahatchet. The essential part of a hammer is the head, a compact solid mass that is able to deliver a blow to the intended target without itself deforming. The impacting surface of the tool is usually flat or slightly rounded; the opposite end of the impacting mass may have a ball shape, as in theball-peen hammer. Someupholstery hammers have amagnetized face, to pick up tacks. In the hatchet, the flat hammer head may be secondary to the cutting edge of the tool.
The impact between steel hammer heads and the objects being hit can createsparks, which may igniteflammable orexplosivegases. These are ahazard in some industries such asunderground coal mining (due to the presence ofmethane gas), or in other hazardous environments such aspetroleum refineries andchemical plants. In these environments, a variety of non-sparking metal tools are used, primarily made ofaluminium orberyllium copper. In recent years, the handles have been made of durable plastic or rubber, though wood is still widely used because of its shock-absorbing qualities and repairability.
Cross-peen hammer,[9] having one round face and one wedge-peen face.
Dead blow hammer delivers impact with very little recoil, often due to a hollow head filled with sand,lead shot or pellets
Demolition hammer
Drilling hammer – a short handled sledgehammer originally used for drilling in rock with a chisel. The name usually refers to a hammer with a 2-to-4-pound (0.91 to 1.81 kg) head and a 10-inch (250 mm) handle, also called a "single-jack" hammer because it was used by one person drilling, holding the chisel in one hand and the hammer in the other.[11] In modern usage, the term is mostly interchangeable with "engineer's hammer", although it can indicate a version with a slightly shorter handle.
Engineer's hammer, a short-handled hammer, was originally an essential components of arailroad engineer's toolkit for working on steam locomotives.[12] Typical weight is 2–4 lbs (0.9–1.8 kg) with a 12–14-inch (30–35 cm) handle. Originally these were often cross-peen hammers, with one round face and one wedge-peen face, but in modern usage the term primarily refers to hammers with two round faces.
Gavel, used by judges and presiding authorities to draw attention
Knife-edged hammer, its properties developed to aid a hammerer in the act of slicing whilst bludgeoning
Lathe hammer (also known as a lath hammer, lathing hammer, or lathing hatchet), a tool used for cutting and nailing woodlath, which has a small hatchet blade on one side (with a small, lateral nick for pulling nails) and a hammer head on the other[13]
Rounding hammer, Blacksmith or farrier hammer. Round face generally for moving or drawing metal and flat for "planishing" or smoothing out the surface marks.
In the swing that precedes each blow, the hammer head stores a certain amount of kinetic energy—equal to the lengthD of the swing times the forcef produced by themuscles of the arm and bygravity. 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 ofanvil, the head can travel only a very short distanced before stopping. Since the stopping forceF times that distance must be equal to the head's kinetic energy, it follows thatF is much greater than the original driving forcef—roughly, by a factorD/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. While the energy delivered to the target increases linearly with mass, it increases quadratically with thespeed (see the effect of the handle, below). High techtitanium 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.[14] A titanium head has about 3%recoil energy and can result in greater efficiency and less fatigue when compared to a steel head with up to 30% recoil.Dead blow hammers use special rubber or steel shot to absorbrecoil 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 andenergy 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 theacceleration during the hammer stroke and increases theenergy 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 mechanicalpile drivers, rely entirely on gravity for acceleration on the down stroke.
A hammer may cause significant injury if it strikes the body. Both manual and powered hammers can causeperipheral neuropathy or a variety of other ailments when used improperly. Awkward handles can causerepetitive stress injury (RSI) to hand and arm joints, and uncontrolled shock waves from repeated impacts can injure nerves and the skeleton. Additionally, striking metal objects with a hammer may produce small metallic projectiles which can become lodged in the eye. It is therefore recommended to wearsafety glasses.
A T-shaped hammer in the upper left corner of the coat of arms ofTampere
The hammer, being one of the most used tools byman, has been used very much in symbols such asflags andheraldry. In the Middle Ages, it was used often in blacksmith guild logos, as well as in many family symbols. Thehammer and pick are used as a symbol of mining.
In mythology, the godsThor (Norse) andSucellus (Celtic andGallo-Roman), and the heroHercules (Greek), all had hammers that appear in their lore and carried different meanings. Thor, the god of thunder and lightning, wields a hammer namedMjölnir. Many artifacts of decorative hammers have been found, leading modern practitioners of this religion to often wear reproductions as a sign of their faith.
A variant, well-known symbol with a hammer in it is thehammer and sickle, which was the symbol of the formerSoviet Union and is strongly linked tocommunism and earlysocialism. The hammer in this symbol represents the industrial working class (and the sickle represents the agricultural working class). The hammer is used in some coats of arms in former socialist countries likeEast Germany. Similarly, the Hammer and Sword symbolizesStrasserism, a strand ofNazism seeking to appeal to the working class. Another variant of the symbol was used for the North Korean party,Workers' Party of Korea, incorporated with anink brush on the middle, which symbolizes bothJuche andSongun ideologies.
InPink Floyd – The Wall, two hammers crossed are used as a symbol for the fascist takeover of the concert during "In the Flesh". This also has the meaning of the hammer beating down any "nails" that stick out.
Thegavel, a small wooden mallet, is used to symbolize a mandate to preside over a meeting or judicial proceeding, and a graphic image of one is used as a symbol of legislative or judicial decision-making authority.
The hammer in the song "If I Had a Hammer" represents a relentless message of justice broadcast across the land. The song became a symbol of thecivil rights movement.
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