Substances in Daily Use- Standard 6 - General Science - Balbharati

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Substances in Daily Use

Exercise

Q. 1 Fill in the blanks using proper words.

(a) Rubber made by vulcanization is a man-made material.

(b) Man-made materials are made by processing natural materials.

(c) Nylon thread was developed simultaneously in New York and London.

(d) Rayon is also known as synthetic silk.


Q. 2 Answer the following questions.

(a) Why did the need for man-made materials arise?

Ans. The need for man-made materials arose because:

  1. It is human nature to strive for newer things and to make life more comfortable
  2. Several man-made substances are easier to use and can be made available in plenty at a low cost
  3. To meet the needs of an increasing population, especially for clothing needs
  4. Man-made substances often have better properties like being water-resistant, lightweight and easy to transport.

(b) Which are the natural materials obtained from plants and animals?

Ans. Natural materials obtained from:

Plants: Cotton, jute, silk (from silkworms), wood, bamboo, rubber (latex from rubber trees)

Animals: Leather, wool

(c) What is vulcanization?

Ans. Vulcanization is a process in which rubber is heated with sulphur for three to four hours. Sulphur is mixed with rubber to give it hardness. The proportion of sulphur in the mixture is determined by the purpose for which the rubber will be used. This process was invented by Charles Goodyear and brought about a revolutionary change in transportation by making hard and tough rubber tyres.

(d) Which natural materials are used to obtain fibres?

Ans. The natural materials used to obtain fibres are:

  1. Cotton (from cotton plants)
  2. Silk (from cocoons of silkworms)
  3. Wool (from animals like sheep)
  4. Jute (from jute plants)

Q. 3 What are we used for?

(a) Soil

Ans. Soil is used for:

  1. Construction (making bricks with clay)
  2. Agriculture (growing plants and crops)
  3. As a natural abiotic substance for various purposes

(b) Wood

Ans. Wood is used for:

  1. Making furniture like tables, chairs, cupboards
  2. Construction purposes
  3. Manufacturing paper
  4. Making various household items

(c) Nylon

Ans. Nylon is used for:

  1. Making clothes
  2. Making fishing nets
  3. Making ropes

(d) Paper

Ans. Paper is used for:

  1. Writing material (notebooks, books)
  2. Packaging delicate articles
  3. Printing newspapers and books
  4. Making various stationery items

(e) Rubber

Ans. Rubber is used for:

  1. Making tyres for vehicles
  2. Making erasers
  3. Making rubber balls and toys
  4. Making rubber bands
  5. Various industrial applications

Q. 4 How is paper manufactured? Write in your own words.

Ans. Coniferous trees like pine are used to make paper. The bark of the logs of these trees removed and the wood is broken into small pieceThe mixture of these pieces and some chemicais kept soaking for a long time.  It helps to form pulp. When the chemical process is completed, fibrous substances from wood pulp are separated, and some dyes are added. The pulp is then passed through rollers, dried to form paper and finally wound on reels.

Q. 5 Give scientific reasons.

(a) We must use cotton clothes in summer.

Ans. Because cotton is a natural fibre that absorbs sweat from the skin and allows air to pass through easily. Synthetic fibres do not absorb sweat and keep the skin moist which may cause skin diseases.

(b) We must observe economy in the use of materials.

Ans. Because many natural materials are limited in availability and take long time to regenerate. Excessive use leads to depletion of natural resources and affects ecological balance.

(c) Saving paper is the need of the hour.

Ans. Because paper is made from trees and excessive use leads to deforestation. To save trees, it is necessary to use paper sparingly as trees are essential for maintaining ecological balance.

(d) Man-made materials have more demand.

Ans. Because they can be manufactured on a mass scale, cost less, are strong and durable, and have special properties like being water-resistant and lightweight.

(e) Humus is a natural material.

Ans. Because humus is formed naturally through decomposition of dead plants and animals by micro-organisms. It is not artificially created by humans but occurs naturally in soil.

Q. 6 Find out.

(1) How is lac obtained from nature?

Ans. Lac is obtained from nature through tiny insects called lac insects (Laccifer lacca). These insects feed on the sap of certain trees and secrete a resinous substance called lac as a protective coating. The lac is deposited on the branches of host trees. This natural lac is collected, processed and purified to obtain shellac, which is used in making polishes, varnishes, and traditional items.

(2) How are pearls obtained?

Ans. Pearls are obtained from oysters and mussels. When a particle like sand enters in its shell, it causes irritation. To protect itself, it secretes some layers. Over time, these layers build up to form a pearl.

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