The word plastics come from the Greek word Plastikos which means ‘to shape’ or ‘able to be moulded’. All plastics are man-made polymers containing repeat units of the same group called monomer. The process by which plastics are made is called polymerization. The starting materials from which plastics are made are obtained from natural gas and crude oil.
The first plastic was made in the 19th century, by a German scientist Friedrik Schonbein. He accidentally produced a highly combustible substance — nitrocellulose by reacting cotton with nitric acid. Since then several others have been made; among them are polythene, polystyrene, polyvinyl chloride (PVC), polypropylene, polyurethane, nylon and polyester. All these plastics have different monomeric units with specific characteristics.
Plastics can be divided into two major groups— thermosetting and thermoplastics— depending upon the way they behave when heated. Thermoplastics such as nylon and polyethylene become soft when heated and harden on cooling and hence can be recycled many times. But thermosetting plastics such as bakelite cannot he softened or melted once they are set.
Plastic money refers to the use of instruments like credit cards instead of cash in business transactions. It is called plastic money because credit cards are made of plastic. At present currency notes, cheques made of paper or coins are used to make payments after a purchase. Credit cards can also be used to withdraw cash from automatic teller machines. Some credit cards are used exclusively for paying call charges in public telephone booths. Plastic money also carries information about its holder in coded form which makes it theft-proof. No one, but the holder is able to use the card.
A satellite that appears to be stationary in the sky is said to be in ‘geostationary’ orbit. It is launched in such a manner that it orbits the earth directly over its equator at a height of 36,000 kms. At that height, its orbital speed is such that it completes one orbit in 24 hours. Since the earth also completes one rotation around its axis in 24 hours, the satellite appears stationary in the sky from earth.
It is a family of newly discovered, the third allotropic form of carbon, quite distinct in structure and properties from the two earlier known forms — graphite and diamond. The first member of this new form of carbon, also called fullerene, was discovered in 1985 by a team of scientists led by Harold Kroto of the University of Sussex, U.K. and Richard Smalley of the Rice University, USA. Unlike graphite which has a plane layer of six-membered carbon rings and diamond which has a three-dimensional network of tetrahedrally bonded carbons, the newly discovered molecules have spherical cage-like structure, such as the famous geodesic dome invented by Buckminster Fuller. That is why the name fullerene. The most stable of these has 60 carbon atoms. The C-60 molecule has a magenta colour.
The term ‘Fly-by-wire’ is applied to automatic computer controlled operation of an aircraft. Instead of conventional mechanical controls operated manually by the pilot, this modern technology uses computers to control all the flight operations of an aircraft. It is extremely reliable, accurate and free from human errors. In this technology, electrical, electronic and computer systems fully replace conventional mechanical systems required for, say, turning the rudder or wing flaps of an aircraft. However, hydraulic or pneumatic systems required for, say, applying brakes to wheels, are only partially replaced.