Similarly, washer (plate3D) in between two tubular parts keeps the motion or fixed in place. The disc shaped washer (plate 3A & D) helps to reduce the frictions between two parts. A disc may start with a ball that is then flattened. In machines the moving parts have to be protected with discs for the protection of the surface as well as smooth movements. The bicycle (plate 3E) paddles are fixed with the discs for smooth movement and protection for surface damage. Turning the key (plate 3B) requires smooth rotational movement which is possible because of the disc fitted inside the mechanism.

SHEET

Plate 4A Fabric	4B Fabric Sheet	4C Bed Sheet	4D Plastic Sheet	4E Metal Foil

(Source: http://www.google.co.in/search?hl=en&q=Sheet&bav=on.2,or.r_gc.r_pw.r_qf.&biw=1328&bih
=574&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=ehUaULanLuSiAfcqoHIAg#um=1&hl
=en&biw=1328&bih=574&tbm=isch&sa=X&ei=GhYaUK7jJI_imAX5_oGQBA&ved=0CEMQvwUoAQ&q
=Linen+Sheet&spell=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=fadb5816affa1c0b ; Aug 2, 2012)

The word ‘sheet’ immediately gives concept of fabric sheet (plate 4A&B), bed-sheet (plate 4C), sheet of a plastic (plate 4D), sheet of water (metaphor), or metal foil (plate 4E). Metaphorically, the attribute of ‘sheet’ characterize the nature of the object. A sheet is a flat object that is separate or separable from the surroundings. Usually it has clear boundaries, for instance 5’x7’ boundary of a bead sheet. Sheet tends to follow an area or contour. In this matter we are aware of various household or industrial materials, which may vary by thickness. A film is a thin sheet or coating. The term is applied to plastic food wrap or thin layer of oil over water. A blanket is thicker sheet. Sheets are formed by various processes.