Knife

This most likely stems from the fact that it is just not a safe thing to do. The name of Australia's most celebrated thoroughbred horse, Phar Lap, derives from the shared Zhuang and Thai word for lightning. This is especially true in more rural areas where carrying a pocket knife is as common as carrying a set of keys. The lightning bolt shape was a symbol of male humans among the Native Americans such as the Apache (a rhombus shape being a symbol for females) in the American Old West. In many places in the United States it is considered bad luck to hand an open, folding blade knife to someone. It is also distinguished from the "fork of lightning". The puukko is always presented handle first as a sign of trust and friendly intentions. The bolt of lightning in heraldry is distinguished from the lightning bolt and is shown as a zigzag with non-pointed ends.

This is especially true in Finland where various non-governmental organizations, clubs and even government agencies traditionally give a puukko (a Finnish fixed-blade hunting/outdoor knife) as a gift to trusted employers or contacts. Flash II (Barry Allen) and III (Wally West) were both granted their superspeed in accidents involving lightning. In some cultures giving a knife as a gift is considered a sign of respect and trust. The comic book character Billy Batson changed into the superhero Captain Marvel by saying the word "Shazam!", which called down a bolt of magic lightning to make the change. Stirring liquids or powders with a knife is considered unlucky; as the rhyme says, "Stir with a knife, stir up strife". Various novels and role playing games with fantasy tint involves wizardry of lightning bolt, weapon embodying the power of lightning, etc. It is common to include a penny, often taped to the blade, with a knife given as a gift which the receiver is to return as "payment". While this is usually typical of cartoons, it has also been employed by regular TV shows and movies.

To avoid such ill luck, the receiver should give a coin in return so as to "pay" for the gift. This has often also been spoofed, with the uttering of certain words or phrases causing flashes of lightning to appear outside of windows (and often scaring or disturbing some characters). In some countries it is traditionally believed that the giving of a knife as a gift to a friend will cut or sever the relationship. It may herald a waking of a great evil or emergence of a crisis. Knives can be sometimes be customised to the user and/or application:. and many other countries, lightning is often employed as an ominous, dramatic sign. Folding knives with locking blades are not considered pen knives and are currently a legal "grey area". In movies and comics of the contemporary U.S.

A special exception exists for penknives (pocket knives) which are legal without reason for possession. These two qualities make oak trees better grounded and more conductive than trees with shallow roots and closed cells. Sikhs). Of all common trees the most frequently struck is the oak, this is due to the deep central root that goes beneath the tree and also the hollow water filled cells that run up and down the wood of the oak's trunk. sgian dubh), or if it is carried for religious reasons (e.g. It is commonly thought that a tree standing alone is more frequently struck, though in some forested areas, lightning scars can be seen on almost every tree. chefs) or if it is part of a national costume (e.g. Occasionally, a tree may explode completely, as in this Giant Sequoia struck in Geneva.

It is however legal to carry a knife if there is a bona fide reason to do so (e.g. If the damage is severe, the tree may not be able to recover, and decay sets in, eventually killing the tree. In general, knives carried in public places are legally considered to be offensive weapons and the carrier can be charged with "possession of an offensive weapon". In following seasons trees overgrow the damaged area and may cover it completely, leaving only a vertical scar. In private almost any kind of knife may be owned with the exception of automatic knives (flick knives, balisongs, switchblades) which are under any circumstances illegal. Since sap is a poor conductor, its electrical resistance causes it to be heated explosively into steam, which blows off the bark outside the lightning's path. Knife possession is only legislated in public places. Trees are frequent conductors of lightning to the ground (photo of a tree being struck by lightning).

include court buildings and federal property (the latter of which technically has a limit of 2.5 inch blades). Fulgurites are evidence that lightning spreads out into branching channels when it strikes the ground. Other restricted areas in the U.S. These are sometimes found under the sandy surfaces of beaches and golf courses, or in desert regions. In some metro areas such as Washington, D.C., going into office buildings or museums, or simply loitering, carrying even small 3" folding knives can be problematic. The heat of lightning which strikes loose soil or sandy regions of the ground may fuse the soil or sand into glass channels called fulgurites. Cities have ordinances further restricting these laws; in San Antonio, TX, it is a violation to carry a folding knife having a locking blade. This is about five times hotter than the surface of the sun.

In some other States, fixed-blade knives are banned, open carry is banned, and sometimes concealed carry of anything except pocket knives is banned. A bolt of lightning can reach temperatures approaching 28,000 kelvins (50,000 degrees Fahrenheit) in a split second. In Texas, for example, individuals may carry knives openly or concealed so long as they are single-edged, and are not daggers, switchblades, or gravity knives (balisong legality is questionable — there have been convictions). One such example is the destruction of the basement insulator of the 250-metre-high central mast of longwave transmitter Orlunda, which led to its collapse. Knife laws vary tremendously. Hot lightning which lasts for more than a second can deposit immense energy, melting or carbonizing large objects. The knife laws of different countries vary, but are generally strict in Western countries. There is sometimes spectacular and unconventional lightning damage.

Even small knives are forbidden on all commercial airliners and are among the illegal imports that may be confiscated at airports by customs staff even if packed in luggage. Due to the precision timing of this type of event, it is a rare (but documented) occurrence. Even multitools like the SwissTool, Gerber multitools, and Leatherman multitools are often frowned upon, due to their having relatively large blades and/or locking ability. This happens only when the heart is at its lowest electrical charge (the very lowest point that would be recorded in an EKG right before the heart recharges for its next beat) when the lightning strikes. Most Western European nations are very unfriendly toward all knives other than small pocket knives and similarly small tools, which are nonetheless not allowed on planes or in certain other venues. The EMP created by a nearby lightning strike can cause cardiac arrest. One exception is Austria, where civilian possession of automatic knives including double-edged automatic OTF ("out The front") daggers is allowed. They are thought to be caused by the rupture of small capillaries under the skin, either from the current or from the shock wave.

Balisongs (butterfly knives) are only slightly less stigmatized, and tend to be treated as switchblades by law enforcement agencies due to their connection with gang activity. The lightning often leaves skin burns in characteristic Lichtenberg figures, sometimes called lightning flowers; they may persist for hours or days, and are a useful indicator for medical examiners when trying to determine the cause of death. Automatic knives (switchblades) are almost universally banned from civilian carry if not possession. A complete physical examination by paramedics or physicians may reveal ruptured eardrums, and ocular cataracts may develop, sometimes more than a year after an otherwise uneventful recovery. chef's knives). Amnesia and confusion of varying duration often result as well. Exceptions may be made for hunting knives, and for knives used for work-related purposes (e.g. Either the electrical or the mechanical force can result in loss of consciousness, which is very common immediately after a strike.

Carrying knives in public is forbidden by law in many countries. The intense heat generated by a lightning strike can cause lung damage, and the chest can be damaged by the mechanical force of rapidly expanding heated air. (These thoughts were stimulated by an article posted on rec.woodworking.). Others incur myocardial infarction and various cardiac arrhythmias, either of which can be rapidly fatal as well. It has the same relative shape for any depth of cut. Many victims suffer immediate cardiac arrest and will not survive without prompt emergency care, which is safe to administer because the victim will not retain any electrical charge after the lightning has struck (of course, the helper could be struck by a separate bolt of lightning in the vicinity). A wedge shape has the property called "scale invariance". The most critical injuries are to the circulatory system, the lungs, and the central nervous system.

On the other hand, if the type of use cannot be predicted, it may be better to sharpen it to a wedge and let the first use bend the edge to an appropriate curve. Ground strikes, in which the bolt lands near the victim and is conducted through the victim via his or her connection to the ground (such as through the feet), can cause great damage. Perhaps this sheds light on the function of razor straps and on the practice of using two angle guides to sharpen a knife. Splash hits occur when lightning effectively bounces off a nearby object and strikes the victim en route to ground. This contrasts to the usual practice of trying to sharpen knives to a wedge near the edge. Counterintuitively, if the victim's skin resistance is high enough, much of the current will flash around the skin or clothing to the ground, resulting in a surprisingly benign outcome. This is a (microscopic) parabola. In a direct hit the electrical charge strikes the victim first.

So, in this case, the ideal cross section is proportional to the square root of the distance from the edge. Lightning can incapacitate humans in 4 different ways:. (That explains the strength per weight of aluminum, compared to steel.) If the force is applied at the edge, the bending torque is proportional to the distance from the edge. While sudden death is common because of the huge voltage of a lightning strike, survivors often fare better than victims of other electrical injuries caused by a more prolonged application of lesser voltage. Both the area taking the force and the lever arm converting force to torque are proportional to thickness, so the bending resistance is proportional to the square of the thickness. Lightning injuries result from three factors: electrical damage, intense heat, and the mechanical energy which these generate. Sheets of material are bent by stretching the outside or compressing the inside. Nearly 2000 persons per year in the world are injured by lightning strikes, and between 25 to 33 % of those struck die.

Assume the knife is thin and the force is applied at the very edge. Several different types of devices, including lightning rods, lightning arresters, and electrical charge dissipaters, are used to prevent or safely redirect lightning strikes. Making some simplifying assumptions about the forces and the knife edge's ability to resist them may shed some light on ideal sharpening. It is advisable to keep appendages away from any attached metallic components once inside (keys in ignition, etc.). In this case the knife should resist bending or breaking. A better location would be inside a vehicle (a crude type of Faraday cage). If a knife is used as a scraper or encounters hard particles in softer materials or is used asymmetrically, there may be a sideways load near the tip. People have been struck in sheds, make shift shelters, etc.

Realigning the edge goes a long way in keeping the knife sharp, as often times, a rolled edge will make an otherwise sharp knife dull. Contrary to popular notion, there is no 'safe' location outdoors. This fine process can effect alignment of the edge. Because people have been struck many kilometers away from a storm, seeking immediate and effective shelter when thunderstorms approach is an important part of lightning safety. Other times the final step is done with a steel. Thunderstorms are the primary source of lightning. It is useful when a knife is still sharp, but has lost that 'scary sharp' edge from use. However, recently the Cassini-Huygens mission fly-by of Venus detected no signs of lightning at all.

It will not cut the edge significantly, but produces a very sharp edge with very little metal loss. Pioneer missions of the '70s and '80s, signals suggesting lightning may be present in the upper atmosphere were detected [10]. This is traditionally done with a leather strap impregnated with abrasive compounds, but can be done on paper, cardstock, or even cloth in a pinch. During the Soviet Venera and U.S. Stropping a knife is sometimes a finishing step. Lightning on Venus is still a controversial subject after decades of study. Rather expensive are sharpening blocks made with corundum. Lightning on Jupiter is estimated to be 100 times as powerful, but fifteen times less frequent, than that which occurs on Earth.

Coated hones, which have an abrasive, sometimes diamonds, on a base of plastic or metal are another kind of hone. However, lightning has been observed within the atmospheres of other planets, such as Venus and Jupiter, and electrical discharges between Jupiter and Io often occur within the gas cloud sent out by Io's volcanos. There are better ways than oil to clean a hone. Lightning requires the electrical breakdown of gas, so lightning cannot exist in the vacuum of space. This is generally bad to do during polishing. These bolts are typically very straight. Oil is sometimes used to lift the metal dust, called swarf, off the stone. The wire unwinds as the rocket climbs, making a convenient path for the lightning to use.

Oil is not to be used on these. It has also been triggered by launching rockets carrying spools of wire into thunderstorms. Generally, these are more costly than oilstones. Lightning struck the Apollo 12 soon after takeoff, and has struck soon after thermonuclear explosions. They are stored in water, and develop a layer of slurry which dulls the edge if you hone the blade as if honing into the stone. Lightning has been triggered directly by human activity in several instances. Water stones (both artificial and natural) come in very fine grits. Because most of these strokes occur inside a cloud, we do not see many of the individual return strokes in a thunderstorm.

Ceramic hones are also common, especially for fine grit size. This is nothing more than the return stroke, the visible part of the lightning stroke. India is another traditional source for stones. All lightning is streak lightning. Arkansas is a traditional source for honing stones, which are traditionally (though a poor practice) used with water or honing oil. One theory about the cause of the Space Shuttle Columbia disaster is that the craft was struck by atmospheric lightning [9]. Honing stones (also called whetstones) come with coarse and fine grits and can be hard or soft describing whether the grit comes free. Researchers have speculated that such forms of upper atmospheric lightning may play a role in the formation of the ozone layer.

If you feel a little bit of pull at the edge or the nail is sightly abraded, you may have a wire burr. The jets lasted under a second, with shapes likened by the researchers to giant trees and carrots. It should come off with no resistance. On July 22, 2002, five gigantic jets between 60 and 70 km (35 to 45 miles) in length were observed over the South China Sea from Taiwan, reported in Nature [8]. To feel for a wire edge, move your thumb lightly across the edge. Lightning was initially observed travelling up at around 50,000 m/s in a similar way to a typical blue jet, but then divided in two and sped at 250,000 m/s to the ionosphere, where they spread out in a bright burst of light. This will flip the burr back and forth as it is ground off. The jet was located above a thunderstorm over the ocean, and lasted under a second.

An alternate method of removing a wire edge is stroking from side to side on a very fine stone, using light strokes. On September 14, 2001, scientists at the Arecibo Observatory photographed a huge jet double the height of those previously observed, reaching around 80 km (50 miles) into the atmosphere. If not removed, it will break off in use, and the knife will instantly become dull. This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons having been energised by the electromagnetic pulse caused by a positive lightning bolt). Use a slighly steeper angle with very light pressure to do so. Elves is a frivolous acronym for Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources. Remove a wire edge (burr) if one forms during sharpening. Elves were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990.

When you pull a knife up the V, the angle is held for you, as long as you hold the blade perpendicular to the base. Their colour was a puzzle for some time, but is now believed to be a red hue. Another variant is the crock stick setup, where two sticks are put into a plastic or wooden base to form a V shape. They occur in the ionosphere 100 km (60 miles) above the ground over thunderstorms. The stone is mounted on a rod and is pulled through these holes, so that the angle remains consistent. Elves often appear as a dim, flattened, expanding glow around 400 km (250 miles) in diameter that lasts for, typically, just one millisecond [7]. Examples of sharpening tools are the clamp-style systems, which use a clamp with several holes with pre-defined angles. They were first recorded on October 21, 1989, on a video taken from the space shuttle as it passed over Australia.

The composition of the stone affects the sharpness of the blade (finer grain produces sharper blades), as does the composition of the blade (some metals take/keep an edge better than others). They are also brighter than sprites and, as implied by their name, are blue in colour. In general, the harder the material to be cut the higher the angle of the edge. Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 40 to 50 km (25 to 30 miles) above the earth. For an extremely durable edge (such as a chisel or drawknife), sharpen to 30 degrees. Research in 2004 by scientists from Tohoku University found that very low frequency emissions occur at the same time as the sprite, indicating that a discharge within the cloud may generate the sprites [6]. Knives that require a tough edge (such as those that chop) sharpen at 20 degrees. Recent research [5] carried out at the University of Houston in 2002 indicates that some normal (negative) lightning discharges produce a sprite halo, the precursor of a sprite, and that every lightning bolt between cloud and ground attempts to produce a sprite or a sprite halo.

Typical knives sharpen at 15 degrees. Sprites were first photographed on July 6, 1989, by scientists from the University of Minnesota and named after the mischievous sprites in the plays of Shakespeare. Very sharp knives sharpen at 10 degrees. Sprites are preceded by a sprite halo that forms because of heating and ionisation less than 1 millisecond before the sprite. A guide is very helpful. Sprites usually occur in clusters of two or more simultaneous vertical discharges, typically extending from 65 to 75 km (40 to 47 miles) above the earth, with or without less intense filaments reaching above and below. The smaller the angle between the blade and stone, the sharper the knife will be, but the faster it will dull. Sprites can occur up to 50 km from the location of the lightning strike, and with a time delay of up to 100 milliseconds.

Knives are sharpened by grinding against a hard surface, typically stone. They appear as luminous reddish-orange, neon-like flashes, last longer than normal lower stratospheric discharges (typically around 17 milliseconds), and are usually spawned by discharges of positive lightning between the cloud and the ground. However, this may also make them brittle. Sprites are now well-documented electrical discharges that occur high above the cumulonimbus cloud of an active thunderstorm. Most high-quality knives are also tempered very hard, so that they will retain an edge longer. This has sometimes been called megalightning. Either use is likely to break off the tip of the blade, or to bend or break the knife beyond repair. However, it is only in recent years that fuller investigations have been made.

Most knives are not intended as pry bars or screwdrivers. Reports by scientists of strange lightning phenomena above storms date back to at least 1886. Steel blades rust easily, but oiling will prevent pitting due to oxidation and tarnish. It is not the same as ball lightning. A knife should be kept clean, dry and sharp. St Elmo's fire was correctly identified by Franklin as electrical in nature. Conversely it can be argued that what is dangerous is not knowing how sharp a knife is and thus how much force to use. In fact, there are only a few pictures of it.

Also, a dull or damaged knife will inflict a worse wound than a relatively 'clean' cut from a sharp knife. Ball lightning is hardly ever seen. Dull knives lead to excessive use of force to cut materials, increasing the chance that the blade may slip and the force will be transferred to an unintended destination such as the user or another person or object. The scientist Coleman was the first to propose this theory in 1993 in Weather, a publication of the Royal Meteorological Society. A sharp knife is often claimed to be a safer knife. One theory that may account for this wider spectrum of observational evidence is the idea of combustion inside the low-velocity region of axisymmetric (spherical) vortex breakdown of a natural vortex (e.g., the 'Hill's spherical vortex'). Knives offered to another person should always be offered handle first. Vertically linked fireballs have been reported.

When checking the blood circle it is best to hold the knife by the blade, otherwise you defeat the purpose. Fireballs have carved trenches in the peat swamps in Ireland. In Boy Scout parlance, an area within the radius of the arm and blade length combined is called the "blood circle". Fireballs have been seen in tornadoes, and they have also split apart into two or more separate balls and recombined. By extension, assume that the knife is going to slip, and look where the blade would go. The object was a glowing globular zone (the breakdown zone?) with a long, twisting, rope-like projection (the funnel?). "Always cut away from yourself" is the basic adage to keep in mind while using a knife. The photograph has appeared in the scientific journal Transactions of the Royal Society.

Chopping knives need blunter angles, out to thirty degrees. A recent photograph by a Queensland ranger, Brett Porter, showed a fireball that was estimated to be 100 meters in diameter. Slicing knives should have sharper angles, down to ten degrees. The typical fireball diameter is usually standardised as 20–30 cm, but ball lightning several meters in diameter has been reported (Singer). 15 to 25 degrees is a good all-around angle. Ball lightning field properties are more extensive than realised by many scientists not working in this field. The edge is sharpened at different angles for different purposes. Japanese research shows that ball lightning has been seen several times without any connection to stormy weather or lightning.

A good serration pattern will stay sharp several times as long as a straight edge. Any complete theory of ball lightning must be able to describe the wide range of reported properties, such as those described in Singer's book "The Nature of Ball Lightning" and also more contemporary research. The points protect the slicing areas from nicks. Several theories have been advanced to describe ball lightning, with none being universally accepted. Serrations on a blade "saw" through the item being cut and stay sharp for a long time. Some later experimenters have been able to briefly produce small luminous balls by igniting carbon-containing materials atop sparking Tesla Coils. For whittling (artistic wood carving) a blade as short as 25mm (1 inch) is common. There is some speculation that electrical breakdown and arcing of cotton and gutta-percha wire insulation used by Tesla may have been a contributing factor, since some theories of ball lightning require the involvement of carbonaceous materials.

Many knives are specific to a particular activity or occupation:. The engineer Nikola Tesla wrote, "I have succeeded in determining the mode of their formation and producing them artificially" (Electrical World and Engineer, 5 March 1904). Some knives, such as the Scottish dirk and Japanese Tanto function in both roles. Ball lightning has been described by eyewitnesses but rarely, if ever, recorded by meteorologists. In general, knives are either working knives (everyday-use blades), or fighting knives. Some have been known to pass through windows and even dissipate with a bang. Knives exist in several styles:. Some make hissing or crackling noises or no noise at all.

Knives can be categorized based on either form or function. They can be fast moving, slow moving or nearly stationary. It handles much like the clip-point. Ball lightning is described as a floating, illuminated ball that occurs during thunderstorms. A drop-point blade is very similar to a clip point, but it features the back convexed down, rather than having a clip taken out of it. [4]. An example is a head knife, used in leatherworking both to scrape down leather (reducing thickness), and to make precise, rolling cuts to form shapes. As a result, the lightning discharge appears to be silent.

It is the strongest knife-shape. An observer may see nearby lightning, but the sound from the discharge is refracted over his head by a change in the temperature, and therefore the density, of the air around him. It's good for scraping, and sometimes chopping. Some cases of "heat lightning" can be explained by the refraction of sound by bodies of air with different densities. This sort of blade is all edge, with no point, and a handle in the middle. In Florida, heat lightning is often seen out over the water at night, the remnants of storms that formed during the day along a seabreeze front coming in from the opposite coast. An ulu (Inuit woman's knife) knife is a sharpened half-circle. Heat lightning can be an early warning sign that thunderstorms are approaching.

The point is actually a second edge on the end of the blade, with a total edge angle of 60-80 degrees. Heat lightning was named because it often occurs on hot summer nights. The edge is straight. Heat lightning (or, in the UK, "summer lightning") is nothing more than the faint flashes of lightning on the horizon from distant thunderstorms. The traditional Japanese tanto knife uses the blade geometry of (1). Most ground-to-cloud lightning occurs from tall buildings, mountains and towers. It is superficially similar to the points on most Japanese long and short swords (katana and wakizashi). Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud from an upward-moving leader stroke.

(6) An Americanized tanto style knife is thick towards the point. Cloud-to-cloud or intercloud lightning is a somewhat rare type of discharge lightning between two or more completely separate cumulonimbus clouds. Sheepsfoot knives are good for whittling, including sheep's hooves. The last special type of cloud-to-ground lightning is staccato lightning, which is nothing more than a leader stroke with only one return stroke. It gives the most control, because the dull back edge is made to be held by fingers. The winds will blow each successive return stroke slightly to one side of the previous return stoke, causing a ribbon effect. (5) A sheepsfoot knife has a straight edge, and a curved dull back. These occur in thunderstorms where there are high cross winds and multiple return strokes.

The Bowie has a clipped blade. A third special type of cloud-to-ground lightning is ribbon lightning. If the false edge is sharpened it increases the knife's effectiveness in piercing. When the discharge fades it leaves behind a string of beads effect for a brief moment in the leader channel. The sharp tip makes the blade exceptional as a pick, or for cutting in tight places. This is a regular cloud-to-ground stroke that contains a higher intensity of luminosity. The back edge of the clip can have a false edge that can be sharpened to make a second edge. Another special type of cloud-to-ground lightning is bead lightning.

(4) A clip point blade is like a normal blade with the tip "clipped" to make the tip thinner and sharper. They are signs of an approaching storm nad are known colloquially as "bolts from the blue". This shape is primarily used for fighting knives (daggers, bayonets) because it can cut in both directions and point in line with the handle. These usually occur miles ahead of the main storm and will strike without warning on a sunny day. The idea is to make a blade that cuts in either direction, with a strong sharp point. In anvil-to-ground lightning, the leader stroke issues forth in a nearly horizontal direction till it veers toward the ground. (3) A double edged or spey blade has two edges. One special type of cloud-to-ground lightning is anvil-to-ground lightning, a form of positive lightning, since it emanates from the anvil top of a cumulonimbus cloud where the ice crystals are positively charged.

Such a knife is better for slicing than a normal knife. This is the second most common type of lightning. This lets a lightweight knife have a larger curve on its edge. Cloud-to-ground lightning is a great lightning discharge between a cumulonimbus cloud and the ground initiated by the downward-moving leader stroke. (2) A curved, trailing-point knife has a back edge that curves upward. Discharges of electricity in anvil crawlers travel up the sides of the cumulonimbus cloud branching out at the anvil top. Therefore, the knife can chop as well as pick and slice. Intracloud lightning is the most common type of lightning which occurs completely inside one cumulonimbus cloud, and is commonly called an anvil crawler.

The curve concentrates force on a small point, making cutting easier. Some lightning strikes take on particular characteristics, and scientists and the public have given names to these various types of lightning. A dull back lets the wielder use fingers to concentrate force; it also makes the knife heavier and stronger for its size. Measured X-ray burst intensity also falls short, with results indicating particle energy 1/20th of the theory's value. (1) A normal blade has a curving edge, and flat back. Cosmic rays of sufficient energy strike the atmosphere on average only once per 50 seconds per square kilometre. There are a variety of knife blade shapes; some of the most common are listed below. Another issue is the amount of energy the theory states is required to initiate the breakdown.

Vanadium, and perhaps molybdenum, also increase corrosion resistance. While there seems to be a strong correlation between gamma-ray events and lightning, there are insufficient events detected to account for the amount of lightning occurring across the planet. Vanadium and molybdenum are important alloy metals because they make the gain size smaller, which improves hardness and toughness. There are problems with the "runaway breakdown" theory, however. These explain its reputation for long wear (the carbides are harder than the metal) and for being harder to sharpen and not taking as good an edge as rustable, low alloy ("carbon") steel (the ceramic particles themselves cannot be sharpened easily.) The bulk hardness and toughness of stainless steel tend to be lower than those of low alloy steel. Additionally, low-frequency radio emissions detected at ground level can detect lightning bolts from upwards of 4000 km away; combining these with gamma-ray burst events detected from above show overlapping positions and timing. Stainless steel usually has particles of chromium (or other alloy metal) carbides. NASA's RHESSI satellite typically reports 50 gamma-ray events per day, and many of these are strong enough to fit the theory.

It is corrosion resistant (though knife steel is less so than higher nickel stainless steel) because, except in acid, one of the metals or one of the oxides is always stable. The presence of these high-energy events match and support the "runaway breakdown" theory, and were discovered through the examination of rocket-triggered lightning, and from satellite monitoring of natural lightning. Stainless steel is steel with very high (12–18%) chromium content. The X-ray bursts typically have a total duration of less than 100 microseconds and have energies extending up to nearly a few hundred keV. Stainless knife steels are high in carbon, but "carbon steel" means there is not also a lot of chromium. It has been recently revealed that most lightning emits an intense burst of X-rays and/or gamma-rays which seem to be produced during the stepped-leader and dart-leader phases just before the stroke becomes visible. Knife steel has fairly low nickel content, because nickel tends to keep steel in the austenitic structure, even when cold. This was initially considered a fringe theory, but is now becoming mainstream because of the lack of other theories.

The blade is then tempered by heating to an intermediate temperature for a period to make it less brittle. These strike other air molecules, releasing more electrons which are accelerated by the storm's electric field, forming a chain reaction of long-trajectory electrons and creating a conductive plasma many tens of meters in length. It is formed as it is quenched, changing it from the austenitic structure that it has at high temperature to a hard, but brittle martensitic structure. Cosmic rays strike an air molecule and release extremely energetic electrons having enhanced mean free paths of tens of centimeters. All knife steel is tempered martensite, which means that a fine-grained crystal structure with lattice irregularities that make it hard. A theory by Alex Gurevich of the Lebedev Physical Institute in 1992 proposes that cosmic rays may provide the beginnings of what he called a runaway breakdown. Some manufacturers, particularly of kitchen knives, make ceramic blades; these are harder and stay sharp longer, but because of their brittleness, chip and break more readily. While there remains a possibility that researchers are failing to encounter the small high-strength regions of the large clouds, the odds of this are diminishing as further measurements continue to fall short.

Forschner/Victorinox make decent, inexpensive kitchen knives; high-end manufacturers include Wüsthof, Global, Henckels and Böker (Tree Brand). However, measurements inside storm clouds to date have failed to locate fields this strong, with typical fields being between 100 and 400 kilovolts per metre. There is typically more demand for exotic alloys in the utility, outdoor, and tactical or combat knife categories than there is in the kitchen knife category. To spontaneously ionise air and conduct electricity across it, an electric field of field strength of approximately 2500 kilovolts per metre is required. The cost of the process restricts it to high-end knives. Many scientists think that positive and negative lightning in a cloud are actually bipolar lightning. The original craft of Damascus steel may be lost, but not being a registered trademark, the name is today used to apply to the equally old but less exotic pattern welding, which creates layered and admired patterns. During the eighties, flight tests showed that aircraft can trigger a bipolar stepped leader when crossing charged cloud areas.

All three are more ductile than typical stainless steels, but have quite a vocal support group despite concerns about health effects of cobalt content. Such a polarised conductor would be able to maintain intense electric fields at its ends, supporting continued leader development in weak-background electric fields. Other manufacturers sometimes use titanium, cobalt, and cobalt containing alloys. This process provides a means for the positive leader to conduct away the net negative charge collected during development, allowing the leader system to act as an extending polarised conductor. Knife manufacturers such as Spyderco and Benchmade typically use 154CM, VG-10, S30V, and CPM440V (also known as S60V), as well as high-speed high-hardness tool steels like D2 and M2. Heinz Kasemir first hypothesised that a lightning leader system actually develops in a bipolar fashion, with both a positive and a negative branching leader system connected at the system origin and containing a net zero charge. A variety of exotic steels and other materials can be used to form blades. An average bolt of positive lightning carries a current of 300 kiloamperes, transfers a charge of up to 300 coulombs, has a potential difference up to 1 gigavolt (a thousand million volts), dissipates enough energy to light a 100 watt lightbulb for up to 95 years, and lasts for tens or hundreds of milliseconds.

Steels having high carbon but low chromium content are prone to rust and pitting if not kept dry. It tends to occur more frequently in winter storms and at the end of a thunderstorm. Chromium is the major alloying element in stainless steels, giving them the 'stainless' quality. Positive lightning has also been shown to trigger the occurrence of upper atmospheric lightning. Stainless and semi-stainless steels include D2, S30V, 154CM, ATS-34, and 440C. Here is a page showing some pictures of positive lightning. Tests done by Razor Edge Systems, and described in their book "The Razor Edge Book of Sharpening" indicate that stainless steel knives hold an edge better than regular steels. At the present time, aircraft are not designed to withstand such strikes, since their existence was unknown at the time standards were set, and the dangers unappreciated until the destruction of a glider in 1999 [3].

Stainless steels have gained popularity in the latter half of the twentieth century because they are highly resistant to corrosion (so they usually only rust under extreme conditions). As a result of their power, positive lightning strikes are considerably more dangerous. Knife blades are usually made of steel; although there are a few knives using materials like high tech ceramic and titanium, these are very uncommon. During a positive lightning strike, huge quantities of ELF and VLF radio waves are generated. A hole in the end of the handles allows the knife to be hung or placed on a lanyard. Research carried out after the discovery of positive lightning in the 1970s showed that positive lightning bolts are typically six to ten times more powerful than negative bolts, last around ten times longer, and can strike several kilometers or miles distant from the clouds. For a large knife, it is desirable that the handle is thick enough that one's fingers just meet one's palm when the knife is gripped tightly. The overall effect is a discharge of positive charges to the ground.

The handle of a knife should be made of a non-slip material. It occurs when the stepped leader forms at the positively charged cloud tops, with the consequence that a negatively charged streamer issues from the ground. In kitchen knives, it keeps chopped items from moving back toward the hand. Positive lightning makes up less than 5 % of all lightning. In piercing, this helps keep the knife from jamming, for example in bone. An average bolt of negative lightning carries a current of 30 kiloamperes, transfers a charge of 5 coulombs, has a potential difference of about 100 megavolts and dissipates 500 megajoules (enough to light a 100 watt lightbulb for 2 months). See 1 Some knives also have a shoulder in which the blade thickens as it meets the handle. This type of lightning is known as negative lightning because of the discharge of negative charge from the cloud, and accounts for over 95% of all lightning.

Additionally, a groove on the blade can reduce surface tension between the blade and the item being cut, thereby allowing easier movement or removal of the blade. Photographs have been taken on which non-connected streamers are visible such as that shown on the right. In reality, its only function is to make knives and swords lighter while sacrificing little strength; on most knives it has more decorative worth. It is possible for streamers to be sent out from several different objects simultaneously, with only one connecting with the leader and forming the discharge path. According to a popular myth, it lets bleeding occur from an artery without removing the knife. This discharge rapidly superheats the leader channel, causing the air to expand rapidly and produce a shock wave heard as thunder. A fuller, sometimes called a blood gutter or blood groove, is a groove on the side, along a blade. Sometimes several strokes will travel up and down the same leader strike, causing a flickering effect.

The blade in turn consists of a tip, a spine, an edge and a heel. Most lightning strikes usually last about a quarter of a second. The bolster functions as a balance point and handguard, to prevent fingers from slipping onto the blade. This "return stroke" is the most luminous part of the strike, and is the part that is really visible. The tang is an extension of the blade into the handle. The region of high current propagates back up the positive stepped leader into the cloud. A knife consists of a tang, a bolster, a blade and a handle. When the two leaders meet, the electric current greatly increases.

. As it does so, a positively charged streamer is usually sent out from the positively charged ground or cloud. The importance of the knife as a weapon has declined as more specialized weapons have been developed, but the knife remains the universal tool. A bolt of lightning usually begins when an invisible negatively charged stepped leader stroke is sent out from the cloud. In the West, multi-purpose pocket knives are commonly carried, to be available anywhere. Lightning can also occur within the ash clouds from volcanic eruptions^[1],[2], or can be caused by violent forest fires which generate sufficient dust to create a static charge. Today, these are not frequently sharpened, and most sharp knives are used in kitchens. This discharge starts as positive streamer and, if it develops as a positive leader, can eventually connect to the descending discharge from the cloud.

Together with the fork and spoon, the knife has been a common eating utensil in the Western world since, at least, the Middle Ages. If the electric field is strong enough, a discharge can initiate from the ground. While the materials have changed over time, the basic design remains the same. The electric field is higher on trees and tall buildings. Later on with advances in smelting and metallurgy the blades were made of bronze, iron, then steel. When a charged step leader is near the ground, opposite charges appear on the ground and enhance the electric field. The first knives were flint or other rock, chipped or ground to an edge, sometimes with a handle. At the same time, electrical energy stored in the electric field flows radially inward into the conductive filament.

Knives have been used as tools and weapons since the Stone Age. The conductive filament grows in length. The blade of a knife is usually pointed and may have one or two cutting edges. During the strike, successive portions of air become conductive as the electrons and positive ions of air molecules are pulled away from each other and forced to flow in opposite directions (stepped channels called step leaders). A knife usually consists of a blade, commonly less than 12 inches (30cm) in length, attached to a handle. It has been suggested by experimental evidence that these discharges are triggered by cosmic ray strikes which ionise atoms, releasing electrons that are accelerated by the electric fields, ionising other air molecules and making the air conductive by a runaway breakdown, then starting a lightning strike. A knife is a sharp-edged hand tool used for cutting. When sufficient negatives and positives gather in this way, and when the electric field becomes sufficiently strong, an electrical discharge occurs within the clouds or between the clouds and the ground, producing the bolt.

Everybody's Knife Bible by Don Paul, ISBN 0938263234. Cumulonimbus clouds that do not produce enough ice crystals usually fail to produce enough charge separation to cause lightning. The surface finish of the blade can be darkened or polished. Cloud-to-ground lightning is less common. The handle can be altered in shape (for better grip) or material (to prevent electric shock or burns). Cloud-to-cloud lightning can appear at this point. The positively charged crystals tend to rise to the top, causing the cloud top to build up a positive charge, and the negatively charged crystals and hailstones drop to the middle and bottom layers of the cloud, building up a negative charge.

Once charged, by whatever mechanism, work is performed as the opposite charges are driven apart and energy is stored in the electric fields between them. This mechanism has two components: the first is that falling droplets of ice and rain become electrically polarised as they fall through the atmosphere's natural electric field, and the second is that colliding ice particles become charged by electrostatic induction. The mechanism by which this happens is still the subject of research, but one widely accepted theory is the polarisation mechanism. The first process in the generation of lightning is the forcible separation of positive and negative charge carriers within a cloud or air.

Positive lightning does not generally fit the above pattern. This rapid restrike effect was probably known in antiquity, and the "strobe light" effect is often quite noticeable. In addition, lightning often contains a number of restrikes, separated by a much larger amount of time, 30 milliseconds being a typical value. It may persist for longer periods with lower current.

The main stroke travels at about 0.1 c (100 million feet per second) and has high current for 100 microseconds or so. Once the ground discharge meets the stepped leader, the circuit is closed, and the main stroke follows with much higher current. When the downward leader is quite close, a small discharge comes up from a grounded (usually tall) object because of the intensified electric field. This initial phase involves a small electric current and is almost invisible compared to the later effects.

An initial discharge, (or path of ionised air), called a "stepped leader", starts from the thundercloud and proceeds generally downward in a number of quick jumps, typical length 50 meters, but taking a relatively long time (200 milliseconds) to reach the ground. The following picture emerged:. Although causes were debated (and are today to some extent), research produced a wealth of new information about lightning phenomena, especially amounts of current and energy involved. The impetus for new research was from the field of power engineering: power transmission lines came into use, and engineers needed to know much more about lightning.

Although experiments from the time of Franklin showed that lightning was a discharge of static electricity, there was little improvement in theory for more than 150 years. His shoes were blown open, parts of his clothes singed, the engraver knocked out, the doorframe of the room split, and the door itself torn off its hinges. While the experiment was underway, a large ball lightning showed up, collided with Richmann's head, and killed him, leaving a red spot. He ran home with his engraver to capture the event for posterity.

He had created a set-up similar to Franklin's, and was attending a meeting of the Academy of Sciences when he heard thunder. The most well-known death during the spate of Franklin imitators was that of Professor Georg Richmann, of Saint Petersburg, Russia. However, experiments involving lightning are always risky and frequently fatal. As news of the experiment and its particulars spread, the experiment was met with attempts at replication.

However, in his autobiography (written 1771-1788, first published 1790), Franklin clearly states that he performed this experiment after those in France, which occurred weeks before his own experiment, without his prior knowledge as of 1752. The rain which had fallen during the storm had soaked the line and made it conductive.. As time passed, Franklin noticed the loose fibers on the string stretching out; he then brought his hand close to the key and a spark jumped the gap. On his end of the string he attached a key and tied it to a post with a silk thread.

During the next thunderstorm, which was in June 1752, he raised a kite, accompanied by his son as an assistant. Whilst waiting for completion of the spire, he got the idea of using a flying object, such as a kite, instead. The Franklin experiment is as follows:. Franklin usually gets the credit, as he was the first to suggest this experiment.