Monthly Archives: October 2022

The Company Becomes the Diwan

• On 12 August 1765, the Mughal emperor appointed the East India Company as the Diwan of Bengal.

• As Diwan, the Company became the chief financial administrator of the territory under its control.

Revenue for the Company

• The company made effort was to increase the revenue as much as it could and buy fine cotton and silk cloth as cheaply as possible.

• Within five years the value of goods bought by the Company in Bengal doubled.
→ Now the revenue collected in Bengal could finance the purchase of goods for export.

• Bengal economy was facing a deep crisis because artisans were deserting villages since they were being forced to sell their goods to the Company at low prices.
→ Agricultural cultivation showed signs of collapse.

• In 1770 a terrible famine killed ten million people in Bengal.

The need to improve agriculture

• Most Company officials began to feel that investment in land had to be encouraged and agriculture had to be improved.

• In 1793, the Company finally introduced the Permanent Settlement.
→ By the terms of the settlement, the rajas and taluqdars were recognised as zamindars.

• They were asked to collect rent from the peasants and pay revenue to the Company which was fixed permanently.

• This would ensure a regular flow of revenue to the Company’and at the same time encourage
the zamindars to invest in improving the land.

The problem

• The zamindars were not investing in improving the quality of land.

• The revenue fixed was too high for the zamindars.

• As long as the zamindars could earn by giving out their land to tenants, they were not interested in
improving the land.

• On the other hand, in the villages, the cultivator found the system extremely oppressive.

A new system is devised

• By the early nineteenth century, many of the Company officials were convinced that the system of revenue had to be changed again to meet the growing expenses.

Mahalwari settlement

• The collectors went from village to village to estimate the land revenue that each village (mahal) had to pay.

• The charge of collecting the revenue and paying it to the Company was given to the village headman, rather than the zamindar.

• This system came to be known as the mahalwari settlement.

The Munro system

• The new system that was devised came to be known as the ryotwar (or ryotwari).

• It was tried on a small scale by Captain Alexander Read.

• It was subsequently developed by Thomas Munro, which was gradually extended all over south India.

Ryotwari system and its problem

• The settlement had to be made directly with the cultivators ( ryots ) who had tilled the land for generations.

• British should act as paternal father figures protecting the ryots under their charge.

• To increase the income from land, revenue officials fixed too high a revenue demand.

• Peasants were unable to pay, ryots fled the countryside, and villages became deserted in many regions.

Crops for Europe

• The British persuaded or forced cultivators in various parts of India to produce other commercial crops:
→ jute in Bengal
→ tea in Assam
→ sugarcane in the United Provinces (now Uttar Pradesh)
→ wheat in Punjab
→ cotton in Maharashtra and Punjab

→ rice in Madras.

• The British used a variety of methods for increasing cultivation of crops that they needed.

• One such crop was Indigo, which had a great worldwide demand.

Why the demand for Indian indigo?

• By the thirteenth century, Indian indigo was being used by cloth manufacturers in Italy, France and Britain to dye cloth.
→ But the price of indigo was very high.

• European cloth manufacturers, therefore, had to depend on another plant called woad to make violet and blue dyes which were pale and dull.
→ Therefore, cloth dyers, however, preferred indigo as a dye.

• The French began cultivating indigo in St Domingue in the Caribbean islands, the Portuguese in Brazil, the English in Jamaica, and the Spanish in Venezuela.

• Between 1783 and 1789 the production of indigo in the world fell by half.

• Cloth dyers in Britain started looking for new sources of indigo supply.

Britain turns to India

• The Company in India looked for ways to expand the area under indigo cultivation.

• By 1810, 95 percent of the indigo imported into Britain was from India.

• Many Company officials left their jobs and numerous Scotsmen and Englishmen came to India and became planters attracted by the prospect of high profits.

How was indigo cultivated?

• There were two main systems of indigo cultivation –  nij and ryoti.

Nij cultivation and problems

• The planter produced indigo in lands that he directly controlled.

• The planters found it difficult to expand the area under nij cultivation.

• Indigo could be cultivated only on fertile lands which were all already densely populated.

• A large plantation required large number of labour at a time when peasants were
usually busy with their rice cultivation.

• It also required many ploughs and bullocks.

• Till the late nineteenth century, planters were therefore reluctant to expand the area under  nij cultivation.

Indigo on the land of ryots

• Under the ryoti system, the planters pressurised the village headmen to sign the contract on behalf of the ryots.
→ Those who signed the contract got cash advances from the planters at low rates of interest to produce indigo.
→ But the ryot to had to cultivate indigo on at least 25 percent of the area under his holding.

• When the crop was delivered to the planter after the harvest, a new loan was given to the ryot, and the cycle started all over again.

• The price provided to the peasants for the indigo they produced was very low and the cycle of loans never ended.

• Indigo also exhaust the soil rapidly.
→ After an indigo harvest the land could not be sown with rice.

The “Blue Rebellion” and After

• In 1859, the indigo ryots felt that they had the support of the local zamindars and village headmen in their rebellion against the planters.

• As the rebellion spread, intellectuals rushed to the indigo districts and wrote of the misery of the ryots, the tyranny of the planters, and the horrors of the indigo system.

• The government set up the Indigo Commission to enquire into the system of indigo production.
→ The Commission held the planters guilty, and criticised them for the coercive methods they used with indigo cultivators.

• After the revolt, indigo production now shifted their operation to Bihar.

• Mahatma Gandhi’s visit in 1917 marked the beginning of the Champaran movement against the indigo planters.

End of Mughal Empire

• Aurangzeb was the last of the powerful Mughal rulers.

• In 1707, after his death, many Mughal governors (subadars) and big zamindars established regional kingdoms.

East India Company Comes East

• Vasco da Gama, a Portuguese explorer, who had discovered this sea route to India in 1498.

• The Portuguese were the first Europeans who came to India. 

• They established their presence in the western coast of India, and had their base in Goa.

• In 1600, the East India Company acquired a charter from the ruler of England.

• By early seventeenth century, the Dutch and the French also arrived on the scene.

• All the companies were interested in buying the same things such as cotton and silk, pepper, cloves, cardamom and cinnamon which created competition and ultimately reduced the profits that could be earned.

• To secure markets, therefore, led to fierce battles between the trading companies.

East India Company begins trade in Bengal

• The first English factory was set up on the banks of the river Hugli in 1651.

• As trade expanded, the Company persuaded merchants and traders to come and settle near the factory. 

• By 1696 it began building a fort around the settlement. 

• Two years later, the Company gained zamindari rights over three villages.

→ One of the villages was Kalikata

(later came to be known as Kolkata).

How trade led to battles

• After the death of Aurangzeb, the Bengal nawabs asserted their power and autonomy.

The Battle of Plassey

• In 1756, Sirajuddaulah became the nawab of Bengal after the death of Alivardi Khan.

• The Company was keen on a puppet ruler so it help one of Sirajuddaulah’s rivals become the nawab without success. 

• Angry Sirajuddaulah asked the Company to stop interfering in the political affairs of his dominion, stop fortification, and pay the revenues.

• After negotiations failed, the Nawab marched with 30,000 soldiers to the English factory at Kassimbazar, captured the Company officials, locked the warehouse, disarmed all Englishmen, and
blockaded English ships. 

→ He then marched to Calcutta to establish his control over the Company’s fort.

• As the news of the fall of Calcutta reached, Company officials in Madras sent forces under the command of Robert Clive.

• In 1757, the Robert Clive-led Company’s army marched against Sirajuddaula at Plassey.

• The Nawab was defeated, as the forces led by Mir Jafar, one of Sirajuddaulah’s commanders, never fought the battle. 

• After the defeat at Plassey, Sirajuddaulah was assassinated and Mir Jafar made the nawab.

• Mir Jafar died in 1765 the mood of the Company had changed. 

• Finally, in 1765 the Mughal emperor appointed the Company as the Diwan of the provinces of Bengal.

• The outflow of gold from Britain entirely stopped after the assumption of Diwani as now revenues from India could finance Company expenses.

Company officials become “nabobs”

• After the Battle of Plassey the actual nawabs of Bengal were forced to give land and vast sums of money as personal gifts to Company officials.

• Many company officials like Clive made vast wealth however, not all Company officials succeeded in making money. 

• Those who managed to return Britain with wealth led flashy lives and flaunted their riches. They were called “nabobs” – an anglicised version of the Indian word nawab.

Company Rule Expands

• After the Battle of Buxar (1764), the Company appointed Residents in Indian states.

• Through the Residents, the Company officials began interfering in the internal affairs of Indian states. 

• Sometimes the Company forced the states into a “subsidiary alliance”. 

→ According to the terms of this alliance, Indian rulers were not allowed to have their independent armed forces.

→ They were to be protected by the Company though they had to pay huge amounts for this

protection. 

→ If Indian rulers failed to make these payments, a part of their territory was to be taken away by the Company.

Tipu Sultan – The “Tiger of Mysore”

• Mysore had grown in strength under the leadership of powerful rulers like Haidar Ali (ruled from 1761 to 1782) and his famous son Tipu Sultan (ruled from 1782

to 1799). 

• In 1785 Tipu Sultan stopped the export of sandalwood, pepper and cardamom through the ports of his kingdom, and disallowed local merchants from trading with the Company.

• He established close relationship with the French in India, and modernised his army with their help.

• Four wars were fought with Mysore (1767-69, 1780-84, 1790-92 and 1799). 

→ In the last – the Battle of Seringapatam – did the Company ultimately win a victory. 

• Tipu Sultan was killed defending his capital Seringapatam, Mysore 

• The former ruling dynasty of the Wodeyars placed and a subsidiary alliance was imposed on the state.

War with the Marathas

• After the defeat in the Third Battle of Panipat in 1761, they were divided into many states under different chiefs ( sardars ) belonging to dynasties such as Sindhia, Holkar, Gaikwad and Bhonsle. 

→ These chiefs were held together in a confederacy under a Peshwa (Principal Minister).

• Anglo-Marathas war were fought between these and the company.

→ The first war that ended in 1782 with the Treaty of Salbai, there was no clear victor. 

→ The Second Anglo- Maratha War (1803-05) resulting in the British gaining Orissa and the

territories north of the Yamuna river including Agra and Delhi. 

→ The Third Anglo-Maratha War of 1817-19 crushed Maratha power, the Peshwa was removed and Company now had complete control over the territories south of the Vindhyas.

The claim to paramountcy

• Under Lord Hastings (Governor- General from 1813 to 1823) a new policy of “paramountcy” was initiated which claimed its power was greater than that of Indian states. 

→ In order to protect its interests it was justified in annexing or threatening to annex any Indian kingdom.

• In the late 1830s the East India Company became worried about Russia as Russia might expand

across Asia and enter India from the north-west.

• They fought a prolonged war with Afghanistan between 1838 and 1842 and established indirect Company rule there. 

• Sind was taken over in 1843. 

• After the death of Maharaja Ranjit Singh in 1839, two prolonged wars were fought with the Sikh

kingdom and in 1849, Punjab was annexed.

The Doctrine of Lapse

• Lord Dalhousie, the Governor-General from 1848 to 1856 devised a policy that came to be known

as the Doctrine of Lapse.

→ It declared that if an Indian ruler died without a male heir his kingdom would “lapse”, that is, become part of Company territory. 

• Many kingdoms were annexed under this rule:

→ Satara in 1848

→ Sambalpur in 1850

→ Udaipur in 1852

→ Nagpur in 1853

→ Jhansi in 1854

→ Awadh in 1856

Setting up a New Administration

• Warren Hastings (Governor-General from 1773 to 1785) played a significant role in the expansion of Company power.

• British territories were broadly divided into administrative units called Presidencies. There were three Presidencies: 

→ Bengal

→ Madras

→ Bombay. 

• Each was ruled by a  Governor and the supreme head of the administration was the Governor-General.

• From 1772 a new system of justice was established. 

• Each district was to have two courts 

→ a criminal court (faujdari adalat) 

→ a civil court (diwani adalat)

• In Civil courts, Maulvis and Hindu pandits interpreted Indian laws for the European district collectors.

• The criminal courts were still under a qazi and a mufti but under the supervision of the collectors.

• The collector main job was to collect revenue and taxes and maintain law and order in his district with the help of judges, police officers and darogas.

The Company army

• From the 1820s, the cavalry requirements of the Company’s army declined because the British empire was fighting in Burma, Afghanistan and Egypt where soldiers were armed with muskets and matchlocks.

• In the early nineteenth century, the British began to develop a uniform military culture.

• The soldiers were given European-style training and were subjected to drill and discipline.

Conclusion

• The East India Company was transformed from a trading company to a territorial colonial power.

• By 1857 the Company came to exercise direct rule over about 63 percent of the territory and 78 percent of the population of the Indian subcontinent.

How Important are Dates?

• Earlier, history was synonymous with dates.

• History is about finding out how things were in the past and how things have changed.

• Previously, history was an account of battles and big events such as:
→ The year a king was crowned.
→ The year he was married and had a child.
→ The year he fought a particular war or battle.
→ The year he died.
→ The year the next ruler succeeded to the throne.

• Now, historians look more towards why and how things happen and not on when things happened.

Which dates?

• The dates we select become vital because we focus on a particular set of events as important.

• If the focus of study changes, a new set of dates will appear significant.

How do we periodise?

• We divide history into different periods in an attempt to capture the characteristics of a time, its central features as they appear to us.

British classification of Indian History

• In 1817, James Mill, a Scottish economist and political philosopher, in his book ‘A History of British India’ divided Indian history into three periods:

→ Hindu
→ Muslim
→ British

• According to Mill, all Asian societies were at a lower level of civilisation than Europe.

Another Classification of Indian history

• Historians have usually divided Indian history into ‘ancient’, ‘medieval’ and ‘modern’.

• This division too has its problems.

→ Because this periodisation is borrowed from the West where the modern period was associated with the growth of all the forces of modernity – science, reason, democracy, liberty and equality.

→ Medieval was a term used to describe a society where these features of modern society did not exist.

• Many historians refers British rule period as ‘colonial’ because in this rule:

→ People did not have equality, freedom or liberty.
→ No economic growth and progress took place.

What is colonial?

• The British came to conquer the country and establish their rule, subjugating local nawabs and rajas.

• British established control over the economy and society, collected revenue to meet all their expenses, bought the goods they wanted at low prices, produced crops they needed for export

• British rule brought about in values and tastes, customs and practices.

• When the subjugation of one country by another leads to these kinds of political, economic, social and cultural changes, we refer to the process as colonisation.

How do We Know?

• Historians used various sources in writing about the modern history of India or last 250 years of Indian history.

Administration produces records

• The official records of the British administration are one of the important sources.

• Every instruction, plan, policy decision, agreement, investigation was written as British believed that the act of writing was important.

• British set up record rooms attached to all administrative institutions as they felt that all important documents and letters needed to be carefully preserved.

Surveys become important

• The British believed that a country had to be properly known before it could be effectively administered, therefore, practice of surveying became common under the colonial administration.

• By the early nineteenth century detailed surveys were being carried out to map the entire country.

• In the villages, revenue surveys were conducted to know the topography, the soil quality, the flora, the fauna, the local histories, and the cropping pattern.

• From the end of the nineteenth century, Census operations were held every ten years which provide
detailed records of the number of people in all the provinces of India, noting information on castes,
religions and occupation.

• Other surveys such as botanical surveys, zoological surveys, archaeological surveys, anthropological surveys, forest surveys also done.

What official records do not tell

• Official records do not tell what other people in the country felt, and what lay behind their actions.

• We need to look these things in unofficial records which are more difficult to get than official records.

• Sources of Unofficial records:
→ Diaries of people
→ Accounts of pilgrims and travellers
→ Autobiographies of important personalities
→ Popular booklets in the local bazaars
→ Newspapers
→ Written ideas of  Leaders and reformers
→ Written records of poets and novelists.

Limitation of Unofficial records

• They were produced by those who were literate.

• From these, we can’t understand how history was experienced and lived by the tribals and the peasants, the workers in the mines or the poor on the streets.

Introduction

→ The layer of air present around the earth is called atmosphere.

→ Atmosphere is composed of 78% of nitrogen, 21% of oxygen, and 1% percent other gases such as carbon dioxide, ozone, water vapour, methane, etc.

Air pollution

→ The phenomenon of contamination of air with unwanted substances so that it becomes harmful for living organisms and non-living substances is known as air pollution.

→ The substances, which cause air pollution, are called air pollutants.

Sources of air pollution

(i) Power plants
(ii) Factories
(iii) Automobiles
(iv) Burning of firewood

Types of air pollutants

(i) Carbon monoxide

→ It is a colourless poisonous gas.

→ It is produced from incomplete burning of fossil fuels.

(ii) Smog

→ It is made up of smoke and fog.

(iii) Sulphur dioxide

→ It is produced from combustion of fuels.

(iv) Nitrogen dioxide

→ It is produced from incomplete burning of fuels.

(v) Chlorofluorocarbons (CFCs)

→ They are released from refrigerators, air conditioners, and aerosol sprays.

→ They cause damage to the ozone layer resulting in the formation of ozone hole.

(vi) Suspended particulate matter

→ It comprises of tiny particles, which remain suspended in air for a long time.

→ They are produced during burning of fossil fuels in power plants, mining, steel making, and other industrial processes.

→ They reduce visibility and cause haze.

→ They cause respiratory diseases on inhalation.

→ Soot released from Mathura refinery has caused yellowing of the marble of Taj Mahal.

Prevention of air pollution

→ Use of clear fuels such as CNG, LPG, and unleaded petrol in public and private transport.

→ Use of renewable sources of energy such as solar, wind, and hydel energy.

→ Planting more and more trees to prevent pollution.

→ Prevent burning of dry leaves and use them in composting.

→ Kyoto protocol is an agreement between various countries for reducing green house emission.

Acid rain

→ It is formed when sulphur dioxide and nitrogen dioxide present in air react with water droplets to form nitric and sulphuric acid.

→ When it rains, it brings these acids along with it, which causes damage to plants, animals, and monuments.

→ Acid rain has caused corrosion of the marble of Taj Mahal

Water pollution

→ The addition of harmful substances to water, as a result of which its physical, chemical, and
biological properties get altered, is called water pollution.

→ Substances that pollute water are called water pollutants.

Sources of water pollution in Ganga river

→ Untreated discharges from textile, paper and sugar mills, and oil refineries.

→ Disposal of agricultural discharge from near-by fields, which are rich in pesticides and weedicides, into the river.

→ Flow of untreated domestic sewage into the river.

→ Cremation of dead bodies into the river.

→ Immersion of idols of gods and goddesses, flowers, garbage, and polythene bags into the river.

→ Ganga Action Plan aimed to reduce the pollution levels in the river.

Types of water pollutants

→ Domestic sewage

→ It is composed of food wastes, detergents, and disease-causing pathogens.

→ The bacteria present in faecal matter of mammals indicate the pollution levels in a river and if such water is consumed, it may cause various diseases.

Industrial waste

→ It is rich in toxic chemicals such as arsenic, fluorides, and lead.

→ It causes toxicity in plants and animals.

→ It affects the soil by causing changes in acidity and growth of worms.

Agricultural waste

→ It is rich in agricultural pesticides and weedicides.

→ It causes ground water pollution.

→ It causes an increase in the population of algae in water.

→ When these algae die, they are acted upon by decomposers, which use lots of oxygen dissolved in water for this purpose.

→ This results in the death of fishes and other aquatic organisms.

Release of Superheated Water

→ The release of superheated water from some industries and nuclear power plants causes thermal pollution of the water bodies.

→ The abrupt change in the temperature of water body can kill the fish and other organisms adapted to particular temperature range.

Methods of preventing water pollution

→ Industrial waste must be chemically treated to remove harmful substances before dumping into the water bodies.

→ Disposal of human and animal excreta into water should be avoided.

→ Sewage water must be treated before releasing into the rivers.

Conservation of water

→ Reusing the waste water from the kitchen (water that has been used to wash vegetables, etc.) to water the plants in the garden.

→ Turning the tap off while brushing or shaving.

→ Checking for leaky taps and fixing them up.

Rainwater harvesting

→ Using improved farming and irrigation techniques

→ Preventing pollution of water

→ Conserving and replenishing ground water

→ Proper removal of silt from water bodies

→ Preventing cutting of trees

→ Prevention of water pollution

→ Proper treatment of industrial waste and domestic waste before their disposal into rivers.

→ Strict implementation of environmental laws in industrial units.

→ Reusing water used in kitchens (such as to wash vegetables) for watering plants.

→ Getting the leaky taps checked and preventing wastage of water.

Potable water

→ Water that is fit for drinking is called potable water.

Methods of obtaining potable water

(i) Physical methods

→ Boiling of water
→ Use of domestic filters such as candle type filter

(ii) Chemical method

→ Use of chlorine tablets

Greenhouse effect

→ Trapping of heat by gases (CO₂ ) in the atmosphere.

→ Gases that cause the greenhouse effect are responsible for increasing the temperature of the Earth and thus contributing to the phenomenon called global warming.

Causes of Green house effect

→ A part of solar radiations cause warming of the earth’s surface.

→ A part of solar radiation is reflected back, which is trapped by the earth’s atmosphere.

→ This phenomenon is called green house effect.

Green house gases

→ These are the gases, which trap the solar radiations, and in this way, are responsible for the increase in the temperature of Earth.

→ The examples include carbon dioxide, methane, nitrous oxide, and water vapours.

Global warming

→ The CO₂ level in atmosphere is increasing due to various human activities such as deforestation and burning of fossil fuels.

→ Build up of CO₂ in the atmosphere will result in a rise in the average temperature of earth’s atmosphere, leading to global warming.

→ Global warming will lead to melting of glaciers and increase in the sea level.

Introduction

→ The moon is the brightest object in the night sky.

→ All natural objects like the stars, the planets, the moon and many other objects in the sky are celestial objects.

The Moon

→ The various shapes of the bright part of the moon as seen during a month are called phases of the moon.

• New Moon day → when moon is not visible
• Full Moon day → when full moon is visible

→ Gap between consecutive new moon day and full moon day is of 15 days.

→ Rotational period and revolution period of moon are the same (almost 29 days).

Moon’s surface

→ Because of lack of atmosphere, one cannot hear any sound on moon.

→ Moon is visible due to reflected sunlight

The Stars

→ All stars emit their own light. They appear small because of large distances from the earth.

→ The sun appears bigger because it is nearer than any other stars on the space.

→ In day time, stars are not visible because of bright sunlight.

→ Stars appear to move from east to west because of earth’s rotation from west to east.

→ Pole star does not appear to move because it is very nearly situated on earth’s rotational axis over the North pole.

Constellations

→ The stars forming a group that has a recognizable shape is called a constellation.

→ Ursa Major also known as the Big Dipper, the Great Bear or the Saptarshi is one of the most famous constellations during summer time.

→ Orion also called the Hunter is another well-known constellation that can be seen during winter in the late evenings.

Solar System

→ The Sun and the celestial bodies which revolve around it form the solar system.

→ Sun is the nearest star from the earth.

→ It consists of large number of bodies such as planets, comets, asteroids and meteors.

→ The gravitational attraction between the Sun and these objects keeps them revolving around it.

Planets

→ Stars twinkle in the night sky, but planets do not.

→ Planets revolve around the sun along definite paths, called orbits.

→ Time taken by a planet to complete one revolution of its orbit is called revolution period.

→ Time taken by a planet to rotate about its axis is called period of rotation.

→ Satellites revolve around planets.

Inner planets

• Mercury

→ Nearest planet to the sun

→ It is seen just before sunrise and just after sunset near horizon. It has no satellite.

• Venus

→ Nearest planet to the earth

→ Brightest planet in the night sky

→ Seen in the eastern sky before sunrise and in the western sky after sunset

→ Also known as morning or evening star

→ Has no satellite and rotates from east to west (sun rises in the west of Venus).

• Earth

→ From space, it appears blue because of 75% water content.

• Mars

→ It appears reddish and therefore, is known as red planet.

Outer planets

• Jupiter

→ Largest planet in the solar system

→ Rotates very fast about its axis and has large numbers of satellites

• Saturn

→ Has prominent ring system and large numbers of satellites

→ Its density is less than water and is the least among the planets

• Uranus and Neptune

→ Both have ring system.

→ Uranus has a tilted rotational axis and appears to roll on its side.

→ Uranus rotates from east to west similar to Venus.

Other members of Solar System

Asteroids

→ Small rocky objects found in large numbers between Mars and Jupiter

Comets

→ Highly elliptical objects

→ Have a bright head and long gaseous tail.

→ Tail is always directed away from the sun.

→ Halley’s comet appears after every 76 years.

Meteors & Meteorites

→ Objects that enter the earth’s atmosphere and burn because of friction with the atmosphere

→ Large meteors that reach earth’s surface are called meteorites.

Artificial satellite

→ Revolves around the earth

→ Used for weather forecasting, remote sensing, communication system, etc.

Introduction

→ Incident Ray: The ray of light which is directed towards the mirror is called incident ray.

→ Reflected Ray: The ray of light which bounces back after reflection is called reflected ray.

→ Normal: It is perpendicular to the reflecting surface at the point of incidence.

→ A plane mirror reflects the ray of light.

Laws of Reflection

(i) ∠i (Angle of incidence) = ∠r (Angle of reflection)

The angle of incident is equal to the angle of reflection

(ii) The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.

→ The laws of reflection are valid in regular as well as irregular or diffused reflections.

Types of Reflections

→ There are two types of reflection:

(i) Regular Reflections: Reflection from a smooth surface like that of a mirror is called regular reflection.

→ Smooth or polished surfaces gives regular reflection.

(ii) Irregular Reflections: When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as diffused or irregular reflection.

→ Uneven of unpolished surfaces gives irregular reflection.

Image formation by a plane mirror

• Lateral inversion: Left part of the candle appears on the right and its right part appears on the left. This is known as lateral inversion.

→ Objects that give their own light are known as luminous objects

→ Objects that are visible because of reflected light are known as illuminated objects.

Multiple Reflections

→ Two mirrors kept parallel to each other forms multiple images of each other.

→ Kaleidoscope works on the principle of multiple reflections.

→ Periscope is an optical device used to see objects that are not along the line of sight.

Dispersion

→ Sunlight consists of several colours.

→ Splitting of white light into different colours is called dispersion.

• Number of image formed in multiple reflection = (360°/angle between two plane mirror) – 1

Human eye

→ The image forms on retina.

→ Iris controls the size of pupil.

→ Pupil controls the amount of light.

Blind spot

→ The junction of optic nerve and the retina is called blind spot.

→ No sensory cells are there. Therefore, no vision is possible.

→ Impression of an image persists for second in our brain.

→ Cone cells are sensitive to bright light and rod cells are sensitive to dim light.

→ The disappearance of the cross or the round mark shows that there is a point on the retina which cannot send messages to the brain when light falls on it.

Protection of Human Eye

• To protect your eyes, the following points should be remembered:

→ Avoid reading in dim light.

→ Wash your eyes at least four times a day with clean and cold water.

→ Wash your eyes quickly if dust particles or small insects enter your eye.

→ Visit an eye specialist regularly. Improper vision can cause stress, eyestrain, and even headaches.

→ While reading, maintain a distance of atleast 25 cm between your eyes and the book.

→ Do not rub your eyes. If redness in the eye persists, then consult an eye specialist immediately.

→ Avoid direct exposure to sunlight. Exposure to a large amount of light can harm your retina.

→ Vitamin A (raw carrots, broccoli, green vegetables, cod-liver oil, etc.) is necessary for good

vision.

→ Some persons cannot see since birth and some may loose their eye sight because of a disease.

→ Visually challenged persons try to identify things by touching and listening.

→ Braille system is helpful for visually challenged persons.

→ Many Indian languages can be read using the Braille system.

Chapter 15 Some Natural Phenomena notes class 8th science

• A Natural Phenomenon is anything that occurs on its own in nature without any kind of human intervention.
• For example, the weather of a place, fog, storms, winds, tides, volcanic eruptions and cyclones all can be categorized as natural phenomena.
• Some natural phenomena can be destructive such as cyclones, thunderstorms, lightning and earthquakes.
• However, there are some ways with which we can protect and prepare ourselves from these natural disasters.

Figure 1 Examples of Natural Phenomenon

Lightning

• Lightning is an electric discharge or an electric spark that occurs in nature on a major scale. It is caused by the accumulation of charges in the clouds.
• It can be deadly and cause the destruction of life and property.
• In ancient times people were unaware of the cause of lightning and hence they were scared of it. Nowadays, scientists have evolved some precautions that can help us prepare and protect ourselves from this natural phenomenon.

Figure 2 Lightning

The sparks that Greeks knew about

• The Greeks were already aware of the electric charges from 600 BC. They knew that when Amber (a type of resin or synthetic polymer) and fur are rubbed together, then amber can attract light objects like hair.
• Similarly, woollen clothes or polyester clothes also attract hair and can produce a little spark or crackling sound when they are taken off from the body. This is because of electric charges.
• Benjamin Franklin was an American scientist who in 1752 discovered and proved that lightning and spark produced from these clothes are all same things.

What are electric charges?

Figure 3 Electric Charges

• We know that every atom comprises of subatomic particles such as electrons, protons and neutrons.
• All these particles share a common property that they carry electric charges.
• Electrons have a negative charge on them while protons have a positive charge.
• We know that atoms carry a balanced charge however these charges may sometimes become out of order.
• An object will be called electrically neutral if it is carrying a balanced proportion of positive and negative charges.
• An object is called a charged object if there is an imbalance of electrons and protons in it.

Charging by rubbing

• When we rub two objects with each other they get charged due to a transfer of electrons between them.
• For example, if we rub a rubber balloon with animal fur, the balloon is made up of rubber attracts the electrons from the animal fur.
• This results in rubber having an excess of electrons while fur having a shortage of electrons.
• In the same way, if we rub a plastic comb with dry hair the comb acquires some charge.

Types of charges and their interaction

Figure 4 Charged objects

• We know that charged objects may have a shortage or excess of electrons.
• Objects having an excess of electrons are called negatively charged while an object having a shortage of electrons are called positively charged.
• For instance, when a glass rod is rubbed with silk cloth it becomes positively charged while the silk cloth becomes negatively charged.
• These charged objects are now capable of attracting other charged and uncharged objects.
• Objects having the same kind of charges repel each other while objects with different kind of charges attract each other.

Figure 5 Interaction between Charges

What is an electrostatic force?

The force of attraction or repulsion experienced by charged objects is called electrostatic force. 

Figure 6 Electrostatic Force

What is a static electric charge?

Static charge or static electricity is an electric charge which does not move. Static charges are a result when two objects are rubbed with each other. When two surfaces come in contact with each other repeatedly it results in the transfer of electrons from one material to another. The strength of an electric charge depends upon different factors such as:

1. The temperature and humidity
2. Properties of the surface such as its material

Figure 7 Static Charges when woollen sweater and balloon are rubbed together

In opposite to static charge, there is an electric current. The electric current results when the charges flow or move from one point to another. This electric current results in glowing of bulb or working of all the electrical appliances.

Figure 8 Electric Current

Transfer of charges

Charges can transfer from one object to another with the help of conduction and induction:

• Conduction: when a charged object comes in contact with a conductor it results in the transfer of charges through the conductor.

Figure 9 Charging by Conduction

• Induction: When a charged object is brought near a neutral object, it results in shifting in the position of the electrons in the other object.

Figure 10 Charging by Induction

• The process of induction does not involve any physical contact between the charged and uncharged object while the process of conduction requires a physical contact between them.

How the transfer of electric charges leads to conservation of charge?

The net charge on a neutral object is zero. However, when an object receives some electrons from another object, the net negative charge on the first object is equal to the net positive charge of the second object. In this way, charges are conserved during transfer of charges. 

Figure 11 (a) Amber and Cloth both have net zero charge (b) Amber and Cloth are rubbed together (C) Amber and Cloth together have net zero charge

What is an electroscope?

It is a device which can test if an object is charged or not. Abraham Bennet developed a gold leaf electroscope in 1787.

Structure of an electroscope

• Generally, gold and silver are used to construct an electroscope because they are good conductors of electricity. Otherwise, copper and aluminium can also be used.
• It consists of a glass jar having a vertical brass rod.
• The rod is inserted into the jar through the cork.
• The brass rod has a brass disc or horizontal rod attached to it.
• From the other end, two leaves of gold are suspended.

Figure 12 Electroscope

Working of an electroscope

When a charged object touches the brass disc, electric charges get transferred from the brass rod to the gold leaves. As a result, the gold leaves move away from each other depicting the presence of charges.

Figure 13 Working of an electroscope

Discharging and Earthing

• When a charged object loses its charges it is said to be discharged.
• When a charged object transfers its charges to the earth it is called earthing. Generally, every building is provided with earthing to protect it from electrical shocks due to leakage of electric current.

Figure 14 How Earthing Protects us form Shock

Figure 15 How Can we get a Shock Without Earthing

Story of Lightning

Figure 16 Lightning

1. During a thunderstorm, the hot air moves upwards while the raindrops fall downloads.
2. This leads to a separation of charges in the atmosphere.
3. As a result, negative charges get accumulated in the lower ages of the clouds while positive charges accumulate at the upper edges.
4. The ground is accumulated with a positive charge all over.
5. These charges begin to multiply due to the increase in winds and rainfall.
6. Although the air is a poor conductor of electricity due to heavy charges it is unable to restrict the electric flow after some time.
7. The negative charges and positive charges meet which results in the production of electric sparks in the form of a streak of light accompanied by a sound.
8. The streak is called lightning and the whole phenomenon is called electric discharge. This electric discharge can occur between two or more clouds.

Why does lightning strikes tall buildings easily?

We know that lightning occurs as a streak of charges that fall toward the ground. Tall buildings and tall trees can easily conduct the charge towards the ground. The air gap between these buildings and lightning is short hence they are more susceptible to lightning. That does not mean that short objects would not be affected by lightning. 

Lightning safety

One should not stay at an open place during lightning and thunderstorm. Hence as soon as we hear any alert about lightning or thunderstorm, we should rush to a safe place such as a house or a building. If somebody is there in a car or bus, they should stay inside and keep all the doors and windows closed. One should read inside the safe place until the storm lasts.

Do’s and don’ts for lightning safety

Outdoor Safety

1. One should not stay in an open place such as an open vehicle like a motorbike, tractor, or open fields, elevated places, or tall trees.
2. One should not carry an umbrella during the storm.
3. If a person is around a forest they should hide under short trees.
4. One should not get near to any poles on metal objects.
5. One should squat low on the ground instead of laying down.

Figure 17 Lightning Safety

Indoor Safety

1. Lightning is an electric discharge hence one should stay away from electrical wires telephone, cables and metal pipes during a thunderstorm.
2. One may use a cordless phone or a mobile phone in an emergency.
3. One should not come in contact with the running water hence one should avoid bathing.
4. One should unplug all the electrical appliances in the house, for example TV, computers or music systems. Electrical lights do not cause any harm and hence can be kept on.

Figure 18 Lightning Safety

Using a lightning conductor

• In order to protect buildings from lightning, a lightning conductor device is used.
• When the building is being constructed a metallic rod having height more than the building is placed in the walls of the building.
• One end of the rod is in the air while the other end is buried inside the Earth.
• This rod is a conductor and hence during lightning it allows the flow of electric charges to the ground.

Figure 19 Lightning Conductor

Working of a lightning conductor

• The lightning conductor rod consists of pointed ends which are made up of copper wire.
• These copper wires are brought down along the building and are attached to a metallic plate in the ground.
• If lightning hits the building the copper wires carry these charges quickly to the ground.

Earthquakes

• Some natural phenomena such as thunderstorms and cyclones can be predicted by meteorologists. However, there are certain natural phenomena that are uncertain and cannot be predicted accurately. One of them is an earthquake.
• Earthquake is a natural phenomenon that occurs as shaking or trembling of the Earth’s surface.
• It occurs or lasts for a very short span of time.
• The main cause of earthquake is disturbances inside the crust of the earth.
• Deep inside the earth, earthquakes occur all the time however they are not noticeable on the earth’s surface. Sometimes major earthquakes occur on the earth surface which can be destructive.
• Earthquakes can lead to:
  • Loss of life
  • Loss of property such as buildings, dams and bridges
  • Floods
  • Landslides
  • Tsunamis

Figure 20 Destruction due to Earthquake

Cause of an earthquake

Earth’s surface is divided into several layers the crust, mantle, inner core and outer core.

Figure 21 Layers of Earth Surface

The outermost layer of the Earth is divided into several plates. These plates are always moving.

As they move past each other or collide, disturbances are caused in the earth’s crust. These disturbances are called earthquakes or tremors.

Figure 22 Plates on Earth’s Surface

Figure 23 Movement of India’s Earth Plates

Other causes of an earthquake can be:

1. Volcanic eruptions
2. When a meteor hits the Earth surface
3. The nuclear explosion under the Earth surface

Although the causes of an earthquake are clear the scientists cannot predict when the earthquake would occur.

What are seismic zones?

The movement of plates causes an earthquake. Hence the earthquakes are most likely to occur on their boundaries. The areas that lie on the boundaries of these plates are called weak zones, seismic zones or fault zones.

Figure 24 Seismic Zones in India

What is the Richter scale?

• A scale which is used to determine the magnitude or strength of an earthquake is called the Richter scale.
• Destructive earthquakes have a Richter scale magnitude of more than 7.
• A Richter scale is not a linear scale, that is, a magnitude of Richter scale 6 does not imply that it is one and a half times more destructive than an earthquake with a magnitude of 4.
• It rather means that an earthquake of a magnitude of 6 is 100 times more powerful than an earthquake with a magnitude of 4.

Figure 25 Richter Scale and its interpretation

What are seismic waves?

The earthquakes produce waves on the earth surface which are called seismic waves. These waves travel in all the directions on the Earth’s surface.

What is Focus of an earthquake?

The focus of an earthquake is a point inside the earth’s surface where the earthquake originates. It is also called hypocenter.

What is an Epicentre?

The epicentre is a region on the earth’s surface that lies just above the focus of the earthquake is called epicentre. The earthquake does not originate from the epicentre.

Figure 26 Map of Earthquake

What is a seismograph?

• A seismograph is an instrument which can record the seismic waves.
• It contains a metal rod or a pendulum which can vibrate as the earthquake occurs.
• The metal rod is attached to a pen which records the waves on the paper.
• Scientists study these waves and then construct a map of the earthquake.
• This also helps them in determining the power of the earthquake.

Figure 27 Seismograph

Protection against an Earthquake

The buildings located in the seismic zones should be constructed in a way that they can handle major tremors. The following measures should be taken by people to make the houses of buildings quake-safe:

• People should always consult architects and engineers before constructing a new building.
• The roofs of the building should be kept light.
• Timber or mud should be used in the construction of buildings rather than heavy materials.
• The shelf and cupboard should be fixed to the walls so that they do not fall off easily.
• Things such as photo frames, geysers, clocks and other wall hangings should be placed in a place that does not harm anybody if they fall off.
• Buildings should have firefighting equipment as earthquakes may cause fires.

Figure 28 How buildings can be made Quake-Safe

How can people protect themselves from an earthquake?

Indoors safety measures

1. One should hide under a table until the earthquake stops.
2. One should not stay close to heavy and tall objects.
3. If one is in bed they should cover their head with a pillow instead of getting up.

Outdoor safety measures

1. One should find a place which has no tall buildings around or even trees.
2. If a person is inside a car or a bus they should drive slowly to a clear place and be inside until the earthquake stops.

Figure 29 Protection against an Earthquake

Conductors and insulators

Figure 1 Conductors and Insulators of Electricity

• A conductor is any material or substance that allows electricity to flow through it.
• An insulator is any substance or material that prevents the flow of electricity through it.
• Any substance can be called as a conductor of electricity if it allows movement of charges through it.
• The electrons of the conductors can flow freely (they are delocalized) and hence can take electric current through them.
• Insulators do not allow the flow of charges through them because their electrons are tightly packed with their particles.

Figure 2 Delocalized Electrons in a Conductor

• Some materials can allow a little flow of electricity through them and are called poor conductors of electricity.
• Some materials can allow the complete flow of electricity through them and are called good conductors of electricity.
• Every material may conduct electricity in certain situations. For example, air is a bad conductor of electricity but in case of thunderstorms and lightning it carries electric charges through it. Hence, materials are always classifies as good and poor conductors of electricity rather than conductors and insulators.

Can liquids conduct electricity?

• Not all liquids can conduct electricity. However, some of them can be regarded as good conductors of electricity while others as poor conductors of electricity.
• Water containing salts and minerals dissolved in it always conduct electricity.
• Distilled water which does not contain any salts cannot conduct electricity.
• Any solution of acids or bases can also conduct electricity.

Figure 3 Liquids that are Poor and Good Conductors of Electricity

How do liquids conduct electricity?

• Different substances when mixed in water and electricity is passed through them can break apart and form positive and negative particles or ions in the water.
• These ions can pass the electric current through them.
• The more is the number of ions in a liquid the better conductor it is of electricity.
• That is why distilled water is a poor conductor of electricity but salt water is a good conductor of electricity.
• However, many compounds do not form any ions on mixing them with water and therefore they are poor conductors of electricity such as sugar water, oil and alcohol.

Figure 4 Set up to detect if a liquid can conduct electricity

Why LED bulbs are more suitable for testing the electrical conductivity of liquids?

• The electric current often causes heating effect due to which the filament of the bulb gets heated up and glows.
• However, some liquids are capable of conducting electricity but they are weak conductors of electricity. Hence current passes through them but it is not that strong enough to heat up the filament. As a result, the filament would not light up in the case of such liquids.
• However, the LED bulbs can detect the flow of even a small amount of electric current as well. Hence, LED bulbs are suitable for testing the electrical conductivity of liquids.

What is electrolysis?

The effect in which components of a compound get split due to passing an electric current through it is called electrolysis.

Figure 5 Electrolysis Process

What is an electrode?

An electrode is a conductor of electricity that can carry electric current into non-metals and other poor conductors of electricity.

What is an electrolyte?

A solution that breaks into its ions on passing electricity through it is called an electrolyte. Electrolytes are used in the process of electroplating.

What are an anode and cathode?

The positively charged electrode is called anode and the negatively charged electrode is called cathode.

What are anions and cations?

An anion is a negatively charged ion and a cation is a positively charged ion.

Effects of an electric current

• Heating effect: electric current causes heating of the electrical equipment. For example, the filament of a bulb gets heated up due to electric current and therefore glows.
• Mechanical effect: electric current can lead to generation of mechanical energy in appliances. For example, fans and motors work due to this effect.
• Magnetic effect: electric current can give rise to the magnetic field of a substance.
• Chemical effect: electric current can lead to the production of chemical energy or chemical reactions.

Chemical effects of electric current

We know that when an electric current passes through solution it ionizes and breaks down into ions. This is because of chemical reactions that take place when an electric current passes through a solution. Depending on the nature of the solution and the electrodes used, the following effects can be observed in the solution:

1. metallic deposits on the electrodes
2. change in the colour of the solution
3. a release of gas or production of bubbles in the solution

Applications of chemical effects of electric current

Electroplating

• Electroplating is a process in which layer of metal is deposited on another material with the help of electricity.
• Electroplating is used in many industries for depositing a layer of metal with desired characteristics on another metal.
• Different metals used for electroplating are Nickel, Copper, Gold Silver, Tin, Brass, Zinc, Chromium and Platinum.

Process of electroplating

• In order to conduct electroplating right electrodes and electrolytes must be chosen so that metal can deposit over a material.
• For instance, if we want to deposit copper on a material we need an electrolyte that contains copper in it. Similarly, if we need gold on a material we need an electrolyte that contains gold in it.
• Also, we should make sure that the electrode that we are choosing is completely clean.
• The electrodes used are made up of different materials. One of the electrodes is of the same metal of which the electrolyte solution is. The second electrode needs to be the material on which we want to coat another metal.
• For instance, in case we want to plate copper upon brass, one electrode should be of Copper and the other electrode should be of Brass and the electrolyte solution should be any salt which contains copper in it, for example, copper sulphate solution. Consider the diagram given below that describes the process of electroplating of copper.

Figure 6 Electroplating of copper on brass

• Out of these two electrodes the copper electrode acts as the anode (positive electrode) and brass electrode acts as the cathode (negative electrode).
• When electricity is passed through the solution, the copper sulphate breaks down into its ions.
• The copper ions (they have a positive charge) get attracted by the brass electrode while the sulphur ions being negatively charged move towards the copper electrode.
• As a result, copper starts depositing on the brass electrode.
• The process of electroplating takes some time to complete.
• The amount of time that it will take depends upon the strength of the current that is being passed through the circuit and also upon the concentration of the electrolyte.
• As these two are increased the speed of the electroplating process also increases.

Applications of electroplating

Figure 7 Electroplated Objects

• Medical equipment is made up of nickel which is harmful to the human body hence to avoid it from coming in contact with our body a coating of platinum or gold is applied on the surface of nickel.
• Many kitchen equipments, bath taps, parts of cars etc. are covered with chromium coating. Chromium is an expensive metal hence the objects are created with the cheaper metal and chromium coating is provided. Thus, to bring a shining over the objects and prevent them from corrosion chromium coating is used.
• Jewellery makers often make ornaments of less expensive metals and provide a coating of gold or silver upon them.
• The tin cans that are used to store food are actually made up of iron and have a coating of tin on them. Iron can easily react with food and spoil it, however, tin prevents the food from getting reacted with iron and therefore helps in preventing it from getting spoiled easily.
• Bridges and various parts of automobiles are made up of iron because it provides strength. However in order to prevent iron from getting rusted a coating of zinc is provided over it. This method is also called galvanization of iron.

Other applications of Chemical Effect of Electric Current

1. Extracting metals from their ores

Pure metals are extracted from metal ores with the process of electrolysis. Electricity is passed through the metal ores and they get broken down into an ionic lattice and thus the metal is obtained separately. For example, metals like aluminium, magnesium, potassium, sodium and calcium are obtained from their ores in this way.

Figure 8 Extraction of Aluminium

2. Purification of metals

The method of electrolysis is also used to purify a metal by separating it from the impurities. The impure metal is used as an anode which first dissolves in the electrolyte solution and then deposits on the cathode in the pure form. The impurities of the metal remain in the electrolyte solution only. Metals like aluminium, zinc and copper are purified in this way.

Figure 9 Purification of Copper using Electroplating

3. Production of compounds

The electrolysis method is used for the production of some compounds. For example, sodium hydrochlorite

4. Decomposition of compounds

The electrolysis method is also used to decompose a compound into its constituents. For example, water can be decomposed using the process of electrolysis to obtain hydrogen and oxygen.

Figure 10 Decomposing water to separate hydrogen and oxygen

Introduction

→ Sound helps us to communicate with one another and plays an important role in our life.

→ Vibrating body produces sound.

→ In this chapter, we will know about how sound is produced and how we hear them.

Vibration motion

→ to-and-fro or back-and-forth or up-and-down motion of a body.

→ Sound is a form of energy that is produced by producing vibration in an object.

→ Sound cannot move through vacuum.

→ Sound waves are longitudinal waves.

How sound is produced by Humans?

→ In humans, sound is produced by voice box or larynx.

→ When the lungs force air through the slit, the vocal cord vibrates which produce sound.

→ Sometimes, the amplitude of produced sound is so small that we can’t hear them.

→ The muscles attached to the vocal cords can make the cords tight or loose to produce different types of sounds.

→ Different people have different vocal chords. Due to this reason, we all have a different voice quality.

Propagation of Sound

→ Sound requires material medium for propagation.

→ Sound can travel through solid, liquid or gas.

→ Sound cannot travel through vacuum.

→ No sound can be heard in outer spaces.

Frequency

→ Frequency is measure of number of oscillations per second.

→ It is measured in hertz(Hz).

Loudness of sound

→ It is measured in decibel (dB).

→ It depends on amplitude.

• Higher amplitude– louder sound

→ Pitch or shrillness depends on frequency.

• Higher frequency– higher pitch

• Audible sound– Human ear can hear sounds having frequency in the range of 20-20,000 Hz.

Noise

→ Unpleasant sound is called noise.

Noise pollution

→ Presence of unwanted and excessive sound in the environment
→ Noise pollution may cause many health related problems.

Measures to control noise pollution

→ Moving noise producing industries away from residential area.

→ Minimizing the usage of loud speakers.

→ Avoiding unnecessary usage of horns

→ Planting more and more trees.

Human ear

→ Human ear has three parts outer, middle and inner.

→ Shape of the outer part of the ear is like a funnel.

→ In human ear, the eardrum vibrates and passes vibration to the inner ear.

→ The eardrum is like a stretched rubber sheet.

→ Sound vibrations make the eardrum vibrate, from there the signal goes to the brain.

→ Noise level of 85 dB can damage the human ear.

Introduction

→ The vehicles, any object, moving over the surface of another object slows down due to the force of friction applied on it.

Friction

→ It is an opposing force that acts between surfaces in contact moving with respect to each other.

→ It always opposes relative motion between two surfaces.

Cause of friction

→ Friction is cause by the irregularities on the two surfaces in contact.

→ We are able to walk because of the force of friction.

Nature of surfaces for Friction

Smooth surfaces: less friction
Rough surfaces: greater friction

Friction when object is pressed hard

Greater pressing force means Greater friction.

Friction according to mass of object

Greater mass: Greater friction

Sliding friction < Static friction
Rolling friction < Sliding friction

Examples where friction is useful

(i) Walking
(ii) Handling any object
(iii) Rolling motion of ball or wheel

Examples where friction is harmful

(i) Energy dissipation of engine due to friction between surfaces in motion.
(ii) More energy is lost in pulling or pushing an object in rough surfaces.
(iii) Wear and tear of shoe soles and tyres.

(iv) Lubrication: Powder on carom board, oil in machine
(v) Wheel: Wheels reduce friction (because rolling friction < sliding friction).
(vi) Shoe soles and tires are threaded to increase friction for a better grip.
(vii) Fluid friction is minimised by giving suitable shapes to vehicles moving through fluids.

Rolling Friction

→ When a body rolls over the surface of another body, the resistance to its motion is called rolling friction.

Sliding Friction

→ When a body slides over the surface of another body, the resistance to its motion is called sliding friction.

• Rolling friction < Sliding friction

→ Ball bearings change sliding friction into rolling friction.

Fluid Friction

→ Fluid friction is minimised by giving suitable shapes to vehicles moving through fluids.

• Fluid friction is also called drag.

→ Friction force depends upon the speed of the object with respect to the fluid.

→ Friction force depends upon the shape of the and nature of the fluid.