Synthetic Fibres and Plastics (सिंथेटिक फाइबर और प्लास्टिक) Full Chapter Class 8 Science | NCERT Science Class 8 Chapter 3

 SYNTHETIC FIBRES AND PLASTICS

There are two types of fibres:

फाइबर दो प्रकार के होते हैं:

Natural Fiber is fibre which is obtained by plants and animals, like cotton, wool, silk, etc.

Synthetic fiber is man- made fiber. It’s  a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer like rayon, nylon and polymer.

Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

Types of Synthetic Fibres:

    सिंथेटिक फाइबर के प्रकार:

Ryon:  rayon or artificial silk is man-made copy fibre of silk, it is made by chemical treatment of wood pulp. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. 

It is cheaper than silk and can be woven like silk fibres. It can also be dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.

Nylon: it is the first fiber which is 100% man-made without taking any component from animals and plants. It was invented in 1931 and made by mixing coal, water and air. 

Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. So, it became very popular for making clothes. It is used to make -socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains,  parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

Polyester and Acrylic:

पॉलिएस्टर और एक्रिलिक:

Polyester: Polyester is another synthetic fibre. Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material.Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yarn.

PET (polyethylene terephthalate) is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Polyester (Poly+ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. Fabrics are sold by names like polycot, polywool, terrycot, etc. As the name suggests, these are made by mixing two types of fibres. Polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and wool.

Acrylic: it is basically artificial woolen and warm like wool. Clothes made from acrylic are relatively cheap. They are available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres. 

Characteristics of Synthetic Fibres

Some benefits of synthetic fibers are:

Dry up quickly

Durable

Less expensive

Readily available

Easy to maintain

If there are many benefits of synthetic fibers but there is one big disadvantage is melting on heating.  If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.

Plastics

प्लास्टिक

Plastic is also a polymer like the synthetic fibre. Plastic articles are available in all possible shapes and sizes as you can see. Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires. 

Polythene (Poly+ethene) is an example of a plastic. It is used for making commonly used polythene bags.

We have seen there is one plastic which can be bent and another which can’t be bent and gets broken. Lets understand these two types plastics:

Thermoplastics- it is a form of plastic with a very low melting point, this plastic gets deformed easily on heating and can be bent easily. Polythene and PVC are some of the examples of thermoplastics. These are used for manufacturing toys, combs and various types of containers.

Thermosetting plastics- these plastics, when moulded once, can not be softened by heating. It means its melting point is high. Two examples are bakelite and melamine. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics.

Plastics as Materials of Choice

 Nowadays plastic is everywhere from kitchen to operation theater. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metals, plastics are used in cars, aircrafts and spacecrafts, too. List is never ending. 

Here we why plastic is extensively used:

• Plastic is Non-reactive- plastic doesn't react and erodes in the open. Unlike metals, it reacts in the open like if iron is kept in the open it gets eroded.

• Plastic is Light, Strong and Durable - Plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals. They are widely used in industry and for household articles.

• Plastics are Poor Conductors - plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screwdrivers, handles of frying pans are also made of plastic.

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• Plastics find extensive use in the healthcare industry. Some examples of their use are the packaging of tablets, threads used for stitching wounds, syringes, doctors’ gloves and a number of medical instruments.

• Special plastic cookware is used in microwave ovens for cooking food. In microwave ovens, the heat cooks the food but does not affect the plastic vessel. 

• Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating on cookware.

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• Fire-proof plastics: Although synthetic fibre catches fire easily, it is interesting to know that the uniforms of firemen have a coating of melamine plastic to make them flame resistant. 

• 

.

Plastics and the Environment 

A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable

A material which is not easily decomposed by natural processes is termed non-biodegradable.

Therefore, according to definition plastic is non-biodegradable and doesn't go with the environment. plastic takes several years to decompose, it is not environment friendly. It causes environmental pollution.

It also doesn't get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution.

How can we limit the use of plastic?

• Avoid the use of plastics as much as possible. Make use of bags made of cotton or jute when you go shopping.

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• The biodegradable and nonbiodegradable wastes should be collected separately and disposed off separately.

• It is better to recycle plastic waste. Most of the thermoplastics can be recycled.

• Use the 5 R principle. Reduce, Reuse, Recycle, Recover and Refuse. Develop habits which are environment friendly. 

•  Do not throw plastic bags in the water bodies or on the road. 

• Try to minimise the use of plastic materials e.g., use a steel lunch box instead of a plastic one. 

हम प्लास्टिक के उपयोग को कैसे सीमित कर सकते हैं?

• जितना हो सके प्लास्टिक के इस्तेमाल से बचें। खरीदारी के लिए जाते समय रुई या जूट के बैग का प्रयोग करें।

• बायोडिग्रेडेबल और नॉनबायोडिग्रेडेबल कचरे को अलग-अलग एकत्र किया जाना चाहिए और अलग-अलग निपटाया जाना चाहिए।

• प्लास्टिक कचरे को रिसाइकिल करना बेहतर है। अधिकांश थर्माप्लास्टिक को पुनर्नवीनीकरण किया जा सकता है।

• 5 आर सिद्धांत का प्रयोग करें। कम करें, पुन: उपयोग करें, रीसायकल करें, पुनर्प्राप्त करें और मना करें। ऐसी आदतें विकसित करें जो पर्यावरण के अनुकूल हों।

•  प्लास्टिक की थैलियों को जलाशयों में या सड़क पर न फेंके।

• प्लास्टिक सामग्री के उपयोग को कम से कम करने का प्रयास करें, उदाहरण के लिए, प्लास्टिक के बजाय स्टील लंच बॉक्स का उपयोग करें।

Summary Ends.

सारांश समाप्त।

  

Introduction | Tracing Changes Through a Thousand Years | (हज़ार वर्षों के दौरान ट्रेसिंग परिवर्तन) Class 7 History , Class 7 NCERT - OUR PAST , CHAPTER -1 ,

 

Class 7 NCERT - OUR PAST , CHAPTER -1

Tracing changes through  thousand years

हज़ार वर्षों के दौरान ट्रेसिंग परिवर्तन

1.Main points to study:

अध्ययन करने के लिए मुख्य बिंदु:

• How maps are designed

• मानचित्र कैसे डिज़ाइन किए जाते हैं 

• How terminology changes with times

• समय के साथ शब्दावली कैसे बदलती है

• Sourcing of historical data.

• ऐतिहासिक डेटा की सोर्सिंग।

• Emergences of new groups and dynasties.

• नए समूहों और राजवंशों का उदय।

• Formulations of new religions 

• नए धर्मों का निर्माण 

• Division of time period.

• समय अवधि का विभाजन।

2. There are two maps given in book (NCERT Class 7th) of India:

2. भारत के पुस्तक (एनसीईआरटी कक्षा 7वीं) में दो मानचित्र दिए गए हैं:

3.First Map was made in 1154 CE by the Arab geographer Al-Idrisi.

3.सबसे पहले 1154 सीई में अरब भूगोलवेत्ता अल-इदरीसी द्वारा बनाया गया था।

 4…..    2 was made in the 1720s by a French cartographer( cartographer is a person who draws a map.

4… दूसरा 1720 के दशक में एक फ्रांसीसी मानचित्रकार द्वारा बनाया गया था (कार्टोग्राफर वह व्यक्ति है जो एक नक्शा खींचता है)।

5. There was a 600 years gap between both maps .

In map1 south India is considered as north India and Sri Lanka is the island at the top. While Map2 looks somewhere similar to today’s map of India shown as the subcontinent, it was made by european sailors and merchants on the voyages.

 

6.Due to huge differences in timeline when Maps were made historians have to keep base or background  i.e context in the mind to read all these to understand or to interpret it in the right way. 

6.समयरेखा में भारी अंतर के कारण जब मानचित्र बनाए गए थे तो इतिहासकारों को इन सभी को समझने या सही तरीके से व्याख्या करने के लिए आधार या पृष्ठभूमि यानी संदर्भ को दिमाग में रखना पड़ता है।

8. Due to changes in times from old to new- it includes change in language,area, social  and political scenario , the context of historical data has also changed. Examples:

9. Today Hindustan is considered as whole new modern India, while in 13th century Minhaj-i-Siraj, a chronicler who was the principal historian of Delhi sultanate, wrote in Persian, 

 He meant Hindustan  the areas of Punjab, Haryana and the lands between the Ganga and Yamuna.His context was based on political sense for lands that were under the Delhi Sultanate  .

10.  Another example  Babur and Amir khusro considered Hindustan as the idea of a geographical and cultural entity, unlike the meaning it carries in today’s context i.e the political and national meanings.

11. Last example: the term foreigner in today's context means who is not an Indian, while earlier it was for a person who was not from a village and not part of the same culture, maybe that was from the same country.  Mainly to city dwellers in Hindi called pardesi or in persian language ajnabi. 

12.Historians and their Sources

12.इतिहासकार और उनके स्रोत

Historian is a person who is an expert in the study of history. To study history of a particular era , historians depend on various resources available at that Era like on coins, inscriptions, architecture and textual records for information.

 

13. As times passed historians more depend on textual records than available resources of information due to discontinuity of information in other resources ,

14. They displaced  other types of information due to difficulty in handling them. While they started reading and writing the records on papers due to its easy and cheap availability. 

People used it to write holy texts, chronicles of rulers, letters and teachings of saints, petitions and judicial records, and for registers of accounts and taxes.

15. Earlier records were documented as a manuscript, which were hard to handle, made and read. Now paper is becoming popular and cheap, manuscripts were getting copied on papers by hand due to non availability of press .

15. पहले अभिलेखों को पांडुलिपि के रूप में प्रलेखित किया जाता था, जिन्हें संभालना, बनाना और पढ़ना मुश्किल था, क्योंकि कागज लोकप्रिय और सस्ता होता जा रहा है, पांडुलिपि को कागजों पर हाथ से कॉपी नहीं मिल रहा था क्योंकि प्रेस की अनुपलब्धता के कारण इस लेखन के कारण कई जानकारी बदल जाती है। 

16. Authors of various chronicles also revise their earlier written chronicles to make corrections and additions. 

Like The fourteenth-century chronicler Ziyauddin Barani wrote his chronicle first in 1356 and another version two years later. Historians came to know, both were very different from each other till they found the next one after years in a library. 

17 New Social and Political Groups 

17. नए सामाजिक और राजनीतिक समूह

18. Now the challenge for historians has increased due to vast development in every area of people's lives. New technologies made their appearance – like the Persian new technologies - wheel in irrigation, the spinning wheel in weaving, and firearms in combat.

 New foods and beverages arrived in the subcontinent – potatoes, corn, chillies, tea and coffee.Those people who are attracted towards wealth and new opportunities attracted to the subcontinent .

19. In the eighth and fourteenth centuries groups like Marathas, Sikhs, Jats, Ahoms and Kayasthas were becoming politically important.

 A Kshatriya caste naming Rajputs were emerging as strong personalities in different monarchs all over the subcontinent. They are not only rulers or chiefs but very brave and loyal soldiers as described by their  poets. 

The legendary Rajput Prince: Maharan Pratap Singh

महान राजपूत राजकुमार: महारान प्रताप सिंह  

20. As people are developing , forests are getting clean. More and more agricultural land was coming up. 

Forest dwellers are forced to move, new people are coming and tilling the lands and becoming peasants.

 These new peasant groups gradually began to be influenced by regional markets, chieftains, priests, monasteries and temples; they had to give taxes.

21. Due to different economic activities, there were significant socio-economic differences emerged which led to formation of JATIS or sub-castes and ranked on the basis of their backgrounds and their occupations.

Ranks were not fixed permanently, and varied according to the power, influence and resources controlled by members of the jati.

22. These jaits have made their own rules, code of conducts and were governed by their Jatis panchayat but they also need to follow the rules of the village in which they were residing.

23. Region and Empire

23. क्षेत्र और साम्राज्य

24.Indian subcontinent were ruled by many different dynasties and left their marks on social, cultural, economic systems in different regions of the subcontinent  after their fall. During their rule these dynasties also had clashes for land and rules, so the area of different states grew and reduced after battles. this also led to emergence of many distinct

and shared traditions: in the realms of governance, the management of the economy, elite   cultures, and languages.

25.  Dynasties like the Cholas, Khaljis, Tughluqs and Mughals were able to build an empire that was pan-regional – spanning diverse regions.while the Delhi Sultan Ghiyasuddin Balban  (1266-1287) explained that he was the ruler of a vast empire that stretched from Bengal (Gauda) in the east to Ghazni (Gajjana) in Afghanistan in the west and included all of south India (Dravida).

Old and New Religions

26. The Indian subcontinent has seen the emergence of new beliefs systems and religions due to various invasions and dynasties. Bramamans were at top positions in kingdoms. Patrons, rulers follow them strictly.

26.  भारतीय उपमहाद्वीप ने विभिन्न आक्रमणों और राजवंशों के कारण नई विश्वास प्रणालियों और धर्मों का उदय देखा है। ब्राह्मण राज्यों में शीर्ष पदों पर थे। संरक्षक, शासक उनका कड़ाई से पालन करते हैं।

27.New religion like Islam brought by invadors and merchants, teaching of Holy Qur'an brought here which belive in one God aspect of whole universe. Like Hinduism, Islam were also spreading like fire and lots of people started following it. While there are many communities under Islam but main are two :

1 Shia 

2 Sunni

Both believe systems are slightly different from each other…

(To know in depth you can read our blog and watch video for more clarity)

(गहराई से जानने के लिए आप हमारे ब्लॉग को पढ़ सकते हैं और अधिक स्पष्टता के लिए वीडियो देख सकते हैं)

https://ynot.membrainsoft.com/2021/08/islam-history-fully-explained-how-islam.html

28 Thinking about Time and Historical Periods

समय और ऐतिहासिक काल के बारे में सोच

Historians don't see time as days, months and years. They consider them as social and economic developments in time.

In british era, Britishers divided history in three parts :

Hinduism

Muslim 

British 

As per the ruler ruled in India but this division ignored the rich diversity of the subcontinent, plus showed the divide and rule policy of Britishers which did more harm than benefits to our country which we are still facing. Many historians still follow this periodisation pattern in history.

29. The Medieval History of India  from the 7th century to 17th century has seen major changes in social, political and economic aspects of this subcontinent. It includes a wide range of early societies – hunter-gatherers, early farmers, people living in towns and villages, and early empires and kingdoms. It also more about the spread of peasant societies, the rise of regional and imperial state formations – sometimes at the cost of pastoral and forest people – the development of Hinduism and Islam as major religions and the arrival of European trading.

30. This ``medieval” period is often contrasted with the “modern” period. “Modernity” carries with it a sense of material progress and intellectual advancement.

Summary ended.

सारांश समाप्त।