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(Source:http://www.google.co.in/search?hl=en&q=scissors+mechanism&bav=on.2,or.r_gc.r_pw.r_qf.&
biw=1332&bih=581&um=1&ie=UTF8&tbm=isch&source=og&sa=N&tab=wi&ei=q8VKUKeGBonqrQf6o
CICw#um=1&hl=en&tbm=isch&sa=1&q=scissors+mechanism+in+ancient+Egypt&oq=scissors+
mechanism+in+ancient+Egypt&gs_l=img.12...1773.11444.0.13710.17.16.0.0.0.0.0.0..0.0...0.0
...1c.1kTph4n0Pnu8&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=de097c59f4dd727b&biw=1332&bih
=581 ; Sept. 8, 2012)
The positions of scissors are part of expansion and contraction paradigm.
The cross blade scissors has three parts (plate 40B) :
· Blade
· Fulcrum and
· Handle
The cutting force of the scissors works on the law of lever. Levers are one of the basic tools that were probably used in prehistoric times. Levers were first described about 260 BC by the ancient Greek mathematician Archimedes (287-212 BC).
The force applied on the blade can be calculated by length of the handle and force applied on the grip of handle. A pair of scissors is an example of two first class levers connected together at the joint known as fulcrum.
Most scissors are best suited to use with the right hand, but left-handed scissors are designed for use by the left. Because scissors have overlapping blades, they are not symmetric. This asymmetry is true regardless of the orientation and 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 further from 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.
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