- Which three objects do you see in the picture ?
2. How did you identify them ?
3. What material are they made of ?
4. Can any one of these materials be used to make all the three objects?
Substances and objects
All substances are made up of very small particles. Objects are made up of substances. Objects have a specific shape, their parts have a specific arrangement, by which we identify them. We use wood, plastic or steel, to make a table, chair or cupboard. These substances have the strength required to make these articles. Also, these substances can be given a desired shape. It means that we consider the properties of substances to use them for making things.
The same substance or material can be used to make many objects. Let us study some such examples. Cotton-cloth, fibre or thread, sarees, handkerchiefs, quilts, mattresses, pillows, etc. Iron – construction steel bars, griddles, (tawa), parts of automobiles, electric poles, tables, cupboards, etc. Aluminium-kitchen utensils, electrical cables, etc.
By studying the properties of substances, we can select substances suitable for our purposes. The substances in everyday use are of two main kinds – natural and man-made substances.
Substances available in nature are called natural substances. Of these, the substances of the first group are obtained from living things. Substances obtained from living things are called biotic substances. Air, soil, water are substances that are not obtained from living things. They are called abiotic substances.
2. How are leather and wool different from jute and cotton? Leather and wool are obtained from animals. They are of animal origin, whereas jute and cotton are substances of plant origin.
3. Do we find plastic, nylon, brass or cement in nature ?
It is human nature to strive for newer things and to try to make life more comfortable. As a result of his efforts, man not only learnt to use natural substances but also began to process them to make new substances. Several such substances are easier to use and can be made available in plenty at a low cost. Therefore, these substances came to be used on a large scale. There are a great many such man-made substances in use today.
New substances produced by processing naturally available substances are called man-made substances.
Earlier irlis or capes made of grass or sackcloth were used for protection from rain. Then cloth umbrellas came into use. Nowadays, the raincoat, school bags and the book covers you use can all be made from plastic.
Delicate articles, perishable fruits, etc. require packing. To pack TV sets, refrigerators, etc. big cartons and thermocol are being used. All these are man-made substances. These substances are water proof or water resistant, lightweight and easy to transport. That is why, they are being used increasingly.
Production of substances
Rubber is of two types, natural and artificial. Natural rubber is obtained from the gum or sap of trees. This sap is called ‘latex’. Rubber has a peculiar odour and it is white in colour.
Vulcanization of rubber
In this process, rubber is heated with sulphur for three to four hours. To give hardness to the rubber, sulphur is mixed in it. The proportion of sulphur in the mixture is determined by the purpose for which the rubber will be used. Erasers, rubber balls, rubber toys all have varying proportions of sulphur in them. In rubber bands, the proportion of sulphur is very small.
Paper is the substance or material formed due to the intertwining of the cellulose fibres in grass, wood, rags or waste paper. Thus, paper is a kind of network of cellulose fibres.
How is paper made ?
Coniferous trees like pine are used to make paper. The bark of the logs of these trees is first removed and the wood is broken into small pieces. The mixture of these pieces and some chemicals is kept soaking for a long time. It helps to form pulp. When the chemical process is completed, the 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. Paper and wood are closely related. To save trees, it is necessary to use paper sparingly.
Synthetic fibres or threads
- From which substances in nature can we get threads or fibre?
2. What are clothes made from? From the time it was first thought that artificial yarn could be produced to meet the clothing needs of an increasing population, much research and progress has taken place in this field. Innumerable kinds of synthetic or artificial threads are now available. Nylon, dacron, terylene, terene, polyester, rayon are the names of various synthetic threads.
Almost all the articles made from natural fibres in the olden days can now be made from synthetic threads. Nylon, rayon, terylene, acrylic are all synthetic threads and many articles in our daily use are made from them.
These threads were invented at the same time in New York and London. Therefore the initials NY of New York and LON from London were combined to name them NYLON. Nylon threads have a shine and are strong, transparent and water resistant. They are used to manufacture clothes, fishing nets, ropes, etc.
Cotton and wood pulp is dissolved in a chemical called sodium hydroxide to make a solution. Threads are obtained from this solution with the help of machines. As these threads have shine and strength, they are said to be ‘synthetic silk’. They appeared to be shining bright like the sun’s rays. Hence they were named ‘Rayon’.
Dacron, Terylene, Terene
Various hydrocarbons obtained from mineral oils are used to make polymer chains. A solution of such a polymer is pressed through a strainer with fine holes. The fibres formed after cooling, are long and unbroken threads. These threads are twisted to obtain yarn. Different types of chemicals are used to make threads of various properties. These different threads have been named variously as dacron, terylene, terene, etc.