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Scissors are a Tool used for cutting thin material which requires little Force . They are used for cutting, for example: Paper , Cardboard , Metal Foil , thin Plastic , Food , Cloth , Rope , and Wire . Scissors can also be used to cut Hair . Unlike a Knife , a pair of scissors consist of two pivoted blades, each called a scissor. Most types of scissors are not particularly sharp; it is primarily the Shearing between the two blades which cuts. Children 's scissors are even less sharp, and the blades are often protected with Plastic . MECHANICS Mechanically, scissors are a first-class, double- Lever with the pivot acting as the Fulcrum . For cutting thick or heavy material, the Mechanical Advantage of a lever can be exploited by placing the material to be cut as close to the fulcrum as possible. For example, if the applied force (i.e., the hand) is twice as far away from the fulcrum as the cutting location (e.g., piece of paper), the force at the cutting location is twice that of the applied force at the handles. Specialized scissors, like Bolt Cutters exploit leverage by having a long handle but placing the material to be cut close to the fulcrum. Scissors cut material by applying a local Shear Stress at the cutting location which exceeds the material's Shear Strength . HISTORY Turkey ]] It is most likely that scissors were invented in 1500 BC in ancient Egypt. http://inventors.about.com/library/inventors/blscissors.htm These were likely shears with the joint at the far end. http://www.everything2.com/index.pl?node=scissors Cross-bladed scissors were invented by Romans around AD 100. An immense stride in perfecting scissors was taken in 1761 when Robert Hinchliffe produced the first pair of modern-day scissors made of hardened and polished cast steel. He lived in Cheney Square , London and was reputed to be the first person who put out a signboard proclaiming himself "fine scissor manufacturer".http://freepages.history.rootsweb.com/~exy1/fh_material/18C_sheffield/ch4.txt In a part of Sweden (now in Finland ) an ironworks was started 1649 in the hamlet "Fiskars" between Helsinki and Turku . In 1830 a new owner started the first cutlery works in Finland, making among others scissors with the trade mark Fiskars . Fiskars Corporation introduced new methods in the manufacturing of scissors in 1967.http://www.fiskars.fi/pdf/Fiskars_history_eng.pdf. MANUFACTURING The blades of scissors are manufactured to be slightly curved; this provides the best cutting performance. The grinding of the curved blades has always been the most demanding task in the manufacturing of scissors. Before the 1960s, mechanizing the grinding process proved difficult. It is a tricky task to move the blade along a curved path against the grinding wheel, and "automated" scissors grinders developed up until that time imitated the manual work. Therefore the machine could hold only one blade at the time, and even then skilled hands were needed to provide the finishing touches. Leonardo Da Vinci has in his notebooks described a wooden grinding wheel with leather circumference coated with a mixture of oil and emery abrasives ''Uppfinningarnas Bok'' Part V, page 266, Norstedt & Söner, Stockholm, 1926. This type of grinding wheel has been in use for a long time in cutlery works; see picture "1962". In 1967, the Fiskars Corporation, {Link without Title} Finland, introduced a new method using surface grinders for scissors. The method is based on the discovery that the slightly curved surface of the blade can be generated by parallel lines; see the picture "1967". Also the contour and the edge can be ground with a formed grinding wheel as shown in the picture "1967". Instead of moving one blade along a curved path, the surface grinder can keep many blades with a magnetic holding device in a rectilinear motion. The edge is in contact with the grinding wheel during one thousandth part of a second and flooded with cutting fluid for several seconds during the motion of the table. By the former "automated" grinders the edge was in contact with the grinding wheel during several seconds. This method could only operate with very soft non-ceramic grinding wheels. The method of formed grinding wheel was not possible with soft wheels. At the World Exhibition in Seville, Spain, in 1992, the vice-president of Fiskars Corporation explained that a man at Fiskars scissors factory in 8 hours grinds the same number of scissors as during one year in 1962 "Form Function Finland, Número especial en español", 1992, page 50, for the World Exhibition in Seville, Spain issued by the Finnish Society of Crafts and Design. Scissors with ergonomic handles date from designs developed in around 1880. Modern versions from 1967 include using plastic handles instead of brass, the flat form of the blades and joining the blades with a rivet instead of a screw. Owing to the precision of the surface grinders one grinding operation is sufficient for each surface and contour of the scissors. KITCHEN SCISSORS Kitchen scissors, also known as ''kitchen shears'', are similar to common scissors. The main difference is the location of the fulcrum. Kitchen scissors have the fulcrum located farther from the handles to provide more leverage and thus more cutting power. High quality kitchen scissors can easily cut through the breastbone of a Chicken . LEFT HANDED SCISSORS Most scissors are best suited to use with the right hand, but ''left handed'' scissors are designed for use by the left. Left handed scissors have handles which are comfortable to hold in the left hand. Because scissors have overlapping blades, they are not symmetric. This asymmetry is true regardless of the orientation and the shape of the handles: the blade that is on top always forms the same diagonal regardless of orientation. Human hands are also asymmetric and when closing the thumb and fingers do not close vertically, but have a lateral component to the motion. Specifically, the thumb pushes out and fingers pull inwards. For right-handed scissors held in the right hand, the thumb blade is closer to the body so that the natural tendency of the right hand is to force the cutting blades together. Conversely, if right-handed scissors are held in the left hand, the natural tendency of the left hand would be to force the cutting blades laterally apart. Furthermore, with right-handed scissors held by the right-hand, the shearing edge is visible, but when used with the left hand the cutting edge of the scissors is behind the top blade, and one cannot see what is being cut. Some scissors are marketed as Ambidextrous . They have symmetric handles so there is no distinction between the thumb and finger handles, and they have very strong pivots so that the blades simply rotate and do not have any lateral give. However, most "ambidextrous" scissors are in fact still right-handed. Even if they successfully cut, the blade orientation will block the view of the cutting line for a left-handed person. True ambidextrous scissors are possible if the blades are double-edged and one handle is swung all the way around (to almost 360 Degrees ) so that the back of the blades become the new cutting edges {Link without Title} . Patents () have been awarded for true ambidextrous scissors. Using scissors designed for the wrong hand is difficult for most people, even for left-handers who have become accustomed to using the more readily available right-handed scissors. They have to unnaturally force the blades together to cut and stretch their necks over the top blade to see what is being cut. This unnatural motion can also cause marks on the hand, sores, and eventually Callus es. SHEARS tool)]] Although often used interchangeably with "scissors," the term ''shears'' is reserved by those in the industry for scissors longer than 15 cm {Link without Title} . Others assert scissors are symmetric whereas shears distinguish between the thumb hole and the finger holehttp://www.canadacutlery.com/product/facts_on_scissors.pdf. Like scissors, shears combine slightly offset jaws to cut material through physical shear, and combine this with Lever s to apply a considerable shear force. Shears are usually intended for cutting much heavier material than scissors. SPECIALIZED SCISSORS Tang Dynasty ( 618 - 907 AD)]] There are several specialized scissors and shears used for different purposes. Some of these are:
In the following, the blades meet and compress the material instead of shearing it so they are technically not scissors:
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