Changes can be of two types, physical and chemical.
Physical changes are changes in the physical properties of substances.
Due to physical chages new substances are not formed.
Physical changes may be reversible.
Examples: crushing a can, glowing of an electric bulb, tearing of paper, mixing of sand and water. (Scroll down to continue …)
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Chemical Changes are changes in which the composition and chemical properties of the substance get changed.
In chemical changes new substances are produced. The most of the chemical changes are irreversible and permanent.
Note: Some chemical changes are reversible, known as reversible chemical changes.
Example: burning of a candle, formation of curd from milk, ripening of fruits.
Some Chemical Reactions in daily life:
Rusting of Iron: Rusting is the process in which iron turns into iron oxide.
It happens when iron comes into contact with water and oxygen. The process is a type of corrosion that occurs easily under natural conditions.
Prevention of Rusting:
By Painting
By Oiling and greasing
By Chromium plating
By Galvanizing
By Alloying
Cooking of food: Cooking causes breakdown of complex molecules of carbohydrates, fats and proteins into smaller molecules.
It is regarded as a decomposition reaction.
Cooked food is easier to digest than uncooked food.
3. Decay of Organic Substances: Microorganisms like fungi and bacteria produce enzymes which break down complex organic compounds into smaller substances.
It is also regarded as a decomposition reaction.
Some substances can be obtained in pure state from their solutions by crystallization.
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Respiration is essential for survival of living organisms.
It releases energy from the food.
The oxygen we inhale is used to breakdown glucose into carbon dioxide and water.
Energy is released in this process.
The breakdown of glucose occurs in the cells of an organism (cellular respiration). (ScrollScroll down to continue…)
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During heavy exercise when the supply of oxygen to our muscle cells is insufficient, food breakdown is by anaerobic respiration (without oxygen)
Types of Respiration:
External respiration also known as breathing refers to a process of inhaling oxygen from the air into the lungs and expelling carbon dioxide from the lungs to the air.
Exchange of gases both in and out of the blood occurs simultaneously.
Internal Respiration: Process in which food is broken down in body cells.
Internal respiration is further classified into two types as aerobic respiration and anaerobic respiration
(a) Aerobic Respiration: Aerobic respiration takes place in the presence of oxygen. Carbon dioxide and water are the end products of aerobic respiration. respiration happens in most of the organisms.
(b) Anaerobic Respiration: Anaerobic respiration takes place in the absence of oxygen.
Anaerobic respiration usually happens in most of the microbes.
Alcohol and carbon dioxide are formed at the end of anaerobic respiration.
In some cases, lactic acid is formed at the end of anaerobic respiration.
Respiration in Plants: Leaves have pores called stomata for gaseous exchange by diffusion.
Stems have openings called lenticels for gaseous exchange by diffusion.
Roots have stomatal pores for gaseous exchange of oxygen dissolved in soil water.
Respiration in Animals: Respiration in animals vary according to their character like:
Earthworm: Earthworms respire through their skin.
Insect: Insects respire through entire body surface.
Fish: Fishes respire through their gills.
Frogs: Frogs respire through their thin, moist and smooth skin when in water and by lungs when on the land.
Respiration in Humans: Inhaled air passes through nostrils into nasal cavity and then into lungs through windpipe.
Breathing is a part of the process of respiration during which an organism takes in the oxygen-rich air and gives out air rich in carbon dioxide.
The respiratory organs for the exchange of gases vary in different organisms.
During inhalation, our lungs expand and then come back to the original state as the air moves out during exhalation.
Increased physical activity enhances the rate of breathing.
In animals like cow, buffalo, dog and cat the respiratory organs and the process of breathing are similar to those in humans.
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Nutrition: It is the mode of taking food by an organism and its utilization by the body.
Nutrients: The components of food that provide nourishment to the body.
All organisms take food and utilise it to get energy for the growth and maintenance of their bodies. (Scroll down to continue …)
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Autotrophs: Autotrophs are the green plants which synthesise their food themselves by the process of photosynthesis.
Photosynthesis: the process of preparation of own food by the Green plants with the help of chlorophyll (found in green plants), carbon dioxide and water taken from the environment in presence of sunlight is known as photosynthesis.
Plants use simple chemical substances like carbon dioxide, water and minerals for the synthesis of food.
Chlorophyll and sunlight are the essential requirements for photosynthesis.
Complex chemical substances such as carbohydrates are the products of photosynthesis.
Solar energy is stored in the form of food in the leaves with the help of chlorophyll.
Oxygen is produced during photosynthesis.
Oxygen released in photosynthesis is utilised by living organisms for their survival.
Fungi derive nutrition from dead, decaying matter.
They are saprotrophs.
Plants like Cuscuta are parasites.
They take food from the host plant.
A few plants and all animals are dependent on others for their nutrition and are called heterotrophs.
Parasitic: Organisms that live on the body of other organisms. All parasitic plants feed on other plants as either:
Partial Parasites: Obtain some of their nutrition from the host,
Example: Painted cup
Total Parasites: Dependent completely on the host for nutrition.
Example: Mistletoe.
Nutrition in plants
Saprophytic: Organisms that obtain nutrition from dead and decaying plant and animal matter.
Mushrooms, moulds and certain types of fungi and bacteria.
Insectivorous Plants: Green plants which obtain their nourishment partly from soil and atmosphere and partly from small insects.
Example: pitcher plant, bladderwort, and venus fly trap.
Symbiosis: Mode of nutrition in which two different individuals associate with each other to fulfil their requirement of food.
Lichens found on tree trunks is the association between algae and fungus.
Algae obtains water from fungus and it in turn obtains food from algae.
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Herbivorous: Animals that eat plants or plant products.
Example: Cow, sheep, goat, deer, elephant, kangaroo, giraffe, etc.
Carnivorous: Animals that eat only flesh of other animals. They never eat plants.
Examples: Tiger, lizard, lion, etc.
Omnivorous: Animals consume plants as well as other animals as their food.
Examples: Bear, dog, human being, etc.
Parasites: Organisms that obtain their food from other animals either by living inside (endoparasites) or outside (ectoparasites) their body.
Examples: Tapeworm and roundworm (inside body), tick and lice (outside body).
Scavengers: Animals which feed on the remains of dead animals preyed by predators. Example: vulture, crows, jackal, etc. (Scroll down to continue …)
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The main digestive glands which secrete digestive juices are:
the salivary glands,
the liver and
(iii) the pancreas.
The human digestive system consists of the alimentary canal and secretory glands.
It consists of:
buccal cavity,
oesophagus,
stomach,
small intestine,
large intestine ending in rectum
anus.
Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body.
The stomach wall and the wall of the small intestine also secrete digestive juices.
The modes of feeding vary in different organisms.
Nutrition is a complex process involving:
ingestion,
digestion,
absorption,
assimilation and
egestion.
Digestion of carbohydrates, like starch, begins in the buccal cavity.
The digestion of protein starts in the stomach.
Bile secreted from the liver, the pancreatic juice from the pancreas and the digestive juice from the intestinal wall complete the digestion of all components of food in the small intestine.
The digested food is absorbed in the blood vessels from the small intestine.
The absorbed substances are transported to different parts of the body.
Water and some salts are absorbed from the undigested food in the large intestine.
The undigested and unabsorbed residues are expelled out of the body as faeces through the anus.
The grazing animals like cows, buffaloes and deer are known as ruminants.
They quickly ingest, swallow their leafy food and store it in the rumen.
Later, the food returns to the mouth and the animal chews it peacefully.
Amoeba ingests its food with the help of its false feet or pseudopodia.
The food is digested in the food vacuole.
It pushes out finger-like pseudopodia which engulf the prey.
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Light is the natural agent that stimulates sight and makes things visible. Light is reflected from all surfaces. It is a form of energy.
Reflection of Light: Bouncing back of light after striking any surface such as a rough surface, Smooth surfce, shiny surface or polished surface, into the same medium, is called reflection of light. (Scroll down to continue …)
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luminous objects: Objects that give out light on their own are called luminous objects.
Examples: Flame, Sun, Glowing bulb
Non-luminous objects: Objects that do not give out light on their own are called non-luminous objects.
Examples: Rocks, Plasic Toys, Walls of room.
The Non – Luuminous objects, reflect light that falls on them.
When the reflected light enters into our eyes from the objects we could see them.
Types of Reflection: (i) Regular Reflection: When a beam of parallel light rays is incident on a smooth and plane surface, the reflected rays will also be parallel. This type of reflection is called Regular Reflection.
The reflection from a plane mirror is an example of regular reflection.
(ii) Diffused or Irregular Reflection: When a parallel beam of light is incident upon a rough or uneven surface, it is reflected in many directions due to presence of irregularities on that.
multiple reflections: If a reflected light ray is reflected again on being incident on another surface, it is termed as multiple reflections.
Multiple reflections are used in periscope, kaleidoscope etc.
Periscopes are used in submarines, war tanks and by soldiers in bunkers to see objects.
In a kaleidoscope, beautiful patterns are formed due to multiple reflections.
Laws of reflection of light:
(i) The angle of incidence is equal to the angle of reflection.
(ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.
Lateral inversion: Lateral inversion is the effect produced by a plane mirror in reversing images from left to right.
Example: Our left hand will appear as right and vice versa.
Characteristics of the image formed by a plane mirror
Size the image formed by a plane mirror is equal to the siz of the object.
The image formed by the plane mirror is left-right inverted.
The image formed by the plane mirror erect and virtual formed behind the mirror.
Since the distance of the object in front of the mirror two mirrors inclined to each other give multiple images.
Sunlight: Sunlight, called white light, consists of seven colours.
dispersion: Splitting of light into its constituent colours is known as dispersion.
Human Eye:
A normal eye can see nearby and distant objects clearly.
Visually challenged persons can read and write using Braille system.
Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.
Parts of Human Eye: (i) Cornea: Transparent bulge on the front surface of the eyeball which protects the eye andhelps in refraction of light.
(ii) Iris: Coloured diaphragm behind the cornea which controls the amount of light entering the eye.
(iii) Pupil: Dark hole in the middle of iris through which light enters the eye. (iv) Eye lens: Transparent, crystalline structure behind pupil and iris. (v) Ciliary muscles: Hole the eye lens in position and control the focal length of the eye lens.
(vi) Retina: Surface of the rear part of the eyeball where the light entering the eye is focused.
(vii) Rods and Cones: Rod cells respond to the brightness of light while cone cells.
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Natural Resources: Resources include everything provide by the nature. They form the wealth of a country.
Types of Natural Resources: (i) Inexhaustible: There are some resources that are present unlimited in nature and will not be exhausted even if used continuously.
Example: Sunlight, Air. (Scroll down to continue …)
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(ii) Exhaustible: These resources are limited and can soon get exhausted because of Coal, petroleum and natural gas are fossil fuels.
Fossil fuels were formed from the dead remains of living organisms millions of yearsago.
Fossil fuels are exhaustible resources.
Coke, coal tar and coal gas are the products of coal.
Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are obtained by refining petroleum.
Coal and petroleum resources are limited.
We should use them judiciously.
Petroleum is mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.
Refining: Refining is the process of refracting the various constituents / fractions of petroleum.
It carried out in a petroleum refinery.
Natural Gas: A very important fuel as it easy to transport through pipes and can be compressed and stored under high pressure as Compressed Natural Gas (CNG).
It causes no pollution and has high calorific value.
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Combustion: The process of burning a substance in the presence of air (oxygen) andundergoes a chemical reaction to produce heat and light. The substances which burn in air are called combustible.
Oxygen (in air) is essential for combustion. During the process of combustion, heat and light are given out. Ignition temperature is the lowest temperature at which a combustible substancecatches fire.
Types of combustion: The type of combustion differs depending on the type of fuel. (Scroll down to continue)
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Based on nature and intensity combustions are classified into three types. They are: (i) Rapid combustion (ii) Spontaneous combustion (iii) Explosion
Flame: It is a zone or burning vapour. The substances which vaporise during burning give flames.
Example: Kerosene oil and molten wax. Inflammable substances have very low ignition temperature. Fire can be controlled by removing one or more requirements essential for producing fire. Water is commonly used to control fires. Water cannot be used to control fires involving electrical equipments or oils.
There are three different zones of a flame – dark zone, luminous zone and non-luminous zone.
Fuel is any material that is burned to obtain energy that can be used to heat or A good fuel must:
Be readily available. Be cheap. Burn easily at a moderate rate.
Produce a large amount of heat. • Not leave behind any undesirable Fuels differ in their efficiency and cost. Fuel efficiency is expressed in terms of its calorific value which is expressed in units of kilo joule per kg.
Types of Fuels: (i) Solid Fuels: Combustible substances which are solid at room temperature.Example: coal, coke, wood, charcoal, etc. (ii) Liquid fuels: Volatile liquids which produce combustible vapour. Example: Petrol,kerosene, alcohol, diesel, etc. (iii) Gaseous fuels: Combustible gases or mixture of combustible gases. Example: Effects of Burning of Fuels: (i) Carbon fuels like wood, coal petroleum release un burnt carbon particles. Theseare dangerous pollutants causing respiratory diseases, such as asthma.
(ii) Incomplete combustion of carbon fuels gives carbon monoxide which is apoisonous gas.
(iii) Increased concentration of carbon dioxide in the air is believed to cause globalwarming.
(iv) Oxides of Sulphur and nitrogen dissolve in rain water and form acids. Such rain is Un burnt carbon particles in air are dangerous pollutants causing respiratoryproblems.
Incomplete combustion of a fuel gives poisonous carbon monoxide gas. Increased percentage of carbon dioxide in air has been linked to global warming.
Oxides of sulphur and nitrogen produced by the burning of coal, diesel and petrol cause Acid rain which is harmful for crops, buildings and soil.
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Biodiversity: Occurrence of innumerable types of organisms and the whole range of their varieties (biotypes) adapted to different climates, environments and areas. Wildlife sanctuary, national park and bio-sphere reserve are names given to the areas meant for conservation and preservation of forest and wild animals. (Scroll down to continue …)
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Biodiversity refers to the variety of living organisms in a specific area.
Plants and animals of a particular area are known as the flora and fauna of that area.
Endemic species are found only in a particular area.
Endangered species are those which are facing the danger of extinction.
Red Data Book contains a record of endangered species.
Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for a specific purpose like breeding.
We should save, reuse and recycle paper to save trees, energy and water.
Reforestation is the restocking of destroyed forests by planting new trees.
Flora: Different types of plants belonging to an area.
Example: Silver ferns, sal, teak, mango, etc.
Fauna: All animals found in an area.
Example: dog, frog, insects, bull, jackal, etc.
Endemic Species: Species of plants and animals found exclusively in a particular area.
These are not naturally found anywhere else.
Extinct Species: Species of plants and animals which have already been lost.
Type of Threatened Species:
(ii) Vulnerable Species: A vulnerable species is a species of animals or plants which are likely to become endangered unless something changes.
Example: Chinkara deerand black buck, golden langur, etc (iii) Rare Species: Species whose population are originally small and scattered in the National Parks: Protective areas reserved exclusively for the betterment of the wildlife. These are established at the approval of legislature.
Example: Hazaribagh National Park in Jharkhand, Desert National Park in Rajasthan.
Sanctuaries: Hunting prohibited areas set up by government are known as sanctuaries. These are only for the protection of wild animals.
Example: Jaldapara in Madarihat (West Bengal), Keoladeo Ghana in Bharatpur (Rajasthan) igration: The regular, periodic, two way movements of birds and some animals from their place of residence to some other place along well defined routes. It is linked to seasonal factors, breeding, shortage of foods, etc.
The sanctuary is known for the migratory birds.
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Reproduction is a process in which the organisms produce the young ones of their own kind. There are two modes by which animals reproduce.
These are: (i) Sexual reproduction, and (ii) Asexual reproduction (Scrolldown to continue …)
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Sexual Reproduction
Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.
The reproductive organs in the female include ovaries, oviducts and uterus.
The reproductive organs in male include testes, sperm ducts and penis.
The ovary produces female gametes called ovum and the testes produce male gametes called sperms. The fusion of ovum and sperm is called fertilization.
zygote: The fertilized egg is called a zygote.
internal fertilization: Fertilization that takes place inside the female body is called internal fertilization. This is observed in human beings and other animals such as hens, cows and dogs.
external fertilization: Fertilization that takes place outside the female body is called external fertilization. This is observed in frogs, fish, starfish, etc.
The zygote divides repeatedly to give rise to an embryo. The embryo gets embedded in the wall of the uterus for further development.
The stage of the embryo in which all the body parts are identifiable is called foetus.
Animals such as human beings, cows and dogs which give birth to young Ones.
Asexual Reproduction: The type of reproduction in which only a single parent is involved is called asexual reproduction. The transformation of the larva into adult through drastic changes is called Asexual Reproduction
budding: In hydra, new individuals develop from buds. This method of asexual reproduction is called budding.
binary fission.: Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.
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Humans become capable of reproduction after puberty. Puberty sets in between the ages of 11 years and 19 years. These children are called adolescents.
The onset of puberty brings about growth of the reproductive organs. Hairs grow at various places on the body.
Breasts develop in girls.
Facial hair (moustache and beard) appear in boys.
Voice of boys become hoarse as voice box enlarges during adolescence.
Children gain height during adolescence.
Puberty: It is the time when sex organs begin to work.
It brings about growth in reproductive organs and changes in the body.
Puberty starts at the beginning of adolescence.
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Reaching the age of Adolescence
The onset of puberty starts much earlier in girls, between 8 and 13 years of age, whereas it starts between 10 and 14 years of age in boys and lasts upto 2 to 4 years.
Changes during Puberty: (i) Increase in Height: The bones of the legs and arms elongate and the individual becomes tall and lanky.
(ii) Changes in Body Shape: In boys, the body becomes more muscular, the shoulder becomes wider.
In girls, the body shows curves in certain parts and the region below the waist become wider and broader.
(iii) Change in Voice: In boys, the voice becomes hoarse and heavy due to the extra growth of larynx (voice box).
In girls, the voice becomes high pitched and shriller.
(iv) Sweat and sebaceous glands: They become more active and secrete more.
(v) Emotional aspects develop.
Periodic cycle of 28 days. The onset of puberty and maturity of reproductive parts are controlled by hormones.
Hormones are secretions of endocrine glands which pour them directly into the blood stream.
Pituitary gland secretes hormones which include growth hormone and hormones that make other glands such as the testes, ovaries, thyroids and adrenals, secrete hormones.
Pancreas secretes insulin, thyroid produces thyroxin and adrenals produce adrenalin.
Testosterone is the male hormone and estrogens, the female hormone.
The uterine wall in females prepares itself to receive the developing fertilised egg.
Menstruation: In case there isno fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood.This is called menstruation.
Sperm and Ovum fuses together to form a zygote.
Sex chromosomes in sperms determine the baby’s gender. Humans have 23 pairs of chromosomes in each cell.
A pair of chromosome forms the sex chromosomes. Males carry XY and females carry XX chromosomes.
If a sperm carrying X fertilises the ovum with X chromosome, then the resulting baby is a girl.
If a sperm carrying Y chromosome fertilises the ovum with X chromosome, then the resulting baby is a boy.
Hence, males are responsible for the gender of the newly formed babies, Not Women.
Reproductive Health: It is important to eat balanced food and maintain personal hygiene during adolescence.
Cleaning of private parts is important to prevent possible infections.
The activity of sweat glands increases in puberty and releases bad odour from the body.
Thus frequent bathing is necessary. Physical exercise keeps the body fit and healthy as it releases lot of sweat.
Peer pressure is best addressed by self-confidence and a healthy lifestyle.
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Force: A push or a pull, that changes or tends to change the state of rest or of uniform motion of an object or changes its direction or shape.
A force arises due to the interaction between two objects.
Force has magnitude as well as direction.Therefore force is a vector quantity.
The SI unit of force is newton. (Scroll down to continue …)
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A change in the speed of an object or the direction of its motion or both implies a change in its state of motion.
Force acting on an object may cause a change in its state of motion or a change in its shape.
Contact Non Contact Forces:
A force can act on an object with or without being in contact with it. Based on Contact the forces are classclassified as Contact Forces and Non Contact Forces.
Contact Forces: The forces act on a body when the source of force touches the body directly.
The point where the force is applied on an object is called the point of application of force (or point of contact).
Examples of Contact Forces:
(i) Muscular Force: The force exerted by the muscles of the body.
We use force acted by muscles of animals like Humans, bullocks, horses and camels to get our activities done.
(ii) Mechanical Force: The force acted by a machine.
Non-Contact Forces:
Non-Contact Forces: Forces which do not involve physical contact between two bodies on which they act.
Examples of Non-Contact Forces:
(i) Magnetic Force: A magnet exerts a non-contact force on objects made of iron, steel, cobalt or nickel.
(ii) Electrostatic Force: The force which result due to repulsion of similar charges or attraction of opposite charges.
(iii) Gravitational Forces: The force that exists between any two bodies by virtue of
Pressure
Pressure: Thrust acting per unit surface area is called pressure.
Thrust
Thrust is the force acting on an object perpendicular to its surface.
In SI system, pressure is measured in newton per square metre which is equal to 1 pascal (Pa).
Like solids, fluids (liquids and gases) also exert pressure.
A solid exerts pressure only in the downward direction due to its weight, whereas liquids and gases exert pressure inall directions.
Hence liquids and gases exert pressure on the walls of their container.
Atmospheric Pressure
Ttmosphere: The thick blanket of air that covers the earth is termed atmosphere.
The pressure exerted by the atmosphere is called atmospheric Pressure.
The tremendous atmospheric pressure surrounding us is not felt by us because the fluid pressure inside our bodies counter-balances the atmospheric pressure around us.
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Friction is the force that resists the motion of one object against another. It is the force felt between two surfaces when one attempts to slide against the other.
Causes of Friction: Friction exists between two surfaces due to irregularities on the surfaces of the objects in contact, interlocking of micro-level irregularities of the two surfaces and ploughing of harder surfaces into smoother surfaces.
Factors Affecting Friction:
(i) Roughness of the surface.
(ii) The extent to which the two surfaces press against each other.
(iii) Nature of the surface· (Scroll doen to continue …)
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Types of Friction: Friction is classified into three types as: Static Friction, Sliding Friction, Rolling Friction. (i) Static Friction: When a body is at rest, the force of friction is called the static friction and is always equal and opposite to the applied force.
limiting friction: The force of friction which acts when the body is just at the verge of sliding on the surface is called limiting friction.
Motion between two contacting surfaces
(ii) Sliding friction: The friction force which opposes the actual relative sliding motion between two contact surfaces.
Sliding friction is smaller than static friction.
(iii) Rolling Friction: The frictional force that exists between two surfaces when a body rolls over the other.
Rolling friction is smaller than sliding friction.
Static friction > Sliding friction > Rolling friction
Effects of Friction
(i) Friction produces heat.
(ii) Friction causes wear and tear.
(iii) Friction opposes motion.
Advantages of Friction
(i) Friction between pen and paper enables us to write on the paper.
(ii) Friction between our feet and the ground allows our movements like standing, walking and running.
(iii) Friction between the surface of the road and tyres of our vehicles allow the vehicles to move without slipping.
Disadvantages of Friction:
(i) Friction causes moving objects to stop or slow down.
(ii) Friction produces heat causing wastage of energy in machines.
(iii) Friction causes wear and tear of moving parts of machinery, soles of shoes, etc.
Friction is a necessary Evil:
As friction is advantageous to us it is considered as a friend but, due to its disadvantages it is a foe.
Depending on the circumstance, friction can be a help or a hindrance.
Thus it is a necessary evil.
Increasing Friction: By pressing the surfaces together more strongly.
For example, when brakes are applied on a bicycle or car, the brake pads press against a moving part of the wheel and the force of friction increases.
Friction can be increased by increasing the roughness of the surfaces in contact.
For example, treading of shoes and tyres is done to increase friction.
Reducing Friction: Friction between the sliding surfaces of two objects can be reduced by making the surfaces in contact smooth by polishing them.
Sliding friction between the moving parts of vehicles and machinery can be reduced by introducing oil, grease, graphite or any other lubricant.
Lubricant: A lubricant is a substance that reduces friction between surfaces in contact. This reduces the heat generated when the surfaces move. Lubricants can also transmit forces, transport foreign particles, or heat or cool the surfaces.
Rolling friction is less than sliding friction. Hence, sliding friction is replaced by rolling friction by using rollers, like ball bearings between the hub and the axles in the moving parts of machines and vehicles.
Friction is reduced by providing wheels,
Examples: suitcase, school bags of kids, etc.
Streamlined shape: Aeroplanes, boats, fishes and birds which move through fluids have bodies of special shape, called streamlined shape, The streamlined shape reduces the friction due to fluid and reduces the energy usage.
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Sound: Vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear. Musical Sound: The sound which produce a pleasing effect on the ear.
Noise: The sounds which produce a jarring or unpleasant effect. (Scroll down to contue …)
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Types of Sound: (i) Audible Sound: Vibrations whose frequency lies between 20 Hz to 20,000 Hz (20 kHz) are heard by human ear.
(ii) Inaudible Sound: The sounds having frequencies above 20,000 Hz and below 20 Hz cannot be heard by the normal human ear.
Low frequency sounds which cannot be heard are called infrasonics.
High frequency sounds which cannot be heard are called ultrasonics. In human beings, the vibration of the vocal cords produces sound.
Sound travels through a medium (gas, liquid or solid). It cannot travel in vacuum.
The eardrum senses the vibrations of sound. It sends vibrations to the inner ear. From there, the signal goes to the brain.
That is how we hear. Higher the frequency of vibration, the higher is the pitch, and shriller is the sound. Unpleasant sounds are called noise.
Excessive or unwanted sounds lead to noise pollution. Noise pollution may pose health problems for human beings. Lack of sleep, hypertension (high bloodpressure), anxiety and many more health disorders may be caused by noise pollution.
A person who is loud sound continuously may get temporary or even permanent impairment of hearing.
Attempts should be made to minimise noise pollution. Silencing devices must be installed in air craft engines, transport vehicles, industrial machines and home appliances. Plantation on the roadside and elsewhere can reduce noise pollution.
Amplitude: The maximum extent of vibration of the vibrating body from its mean position is known as its amplitude.
Time Period: One complete to and fro movement of the pendulum around its mean positionis called one oscillation.
The time taken by the vibrating particle to complete one oscillation is called time period.
Frequency: The number of vibrations made by the vibrating body in one second is known as its frequency. The SI unit of frequency is the hertz (Hz).
Characteristics of Sounds: (i) Loudness: The sensation produced in the ear which enables us to distinguish between a loud and a faint sound. Larger the amplitude of vibration, the louder is the sound produced. It is proportional to square of the amplitude.
(ii) Pitch: The characteristics of sound which distinguishes between a shrill sound and a soft sound.
Higher the frequency of vibration, higher is the pitch and shrillness.
(iii) Quality: Characteristic which enables us to distinguish between musical notes emittedby different musical instruments or voices even though they have the same.
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Materials through which electric current can pass through easily are called electricconductors or conductors of electricity.
Electrical conductivity Or Electric Conductivity: Electrical conductivity is a measure of the ability of a substance to allow the flow of electric current.
Among solids metals and graphite are good conductors which have high electrical conductivity.
Some liquids are also good conductors.
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Pure water or distilled water is a poor conductor of electricity. But the presence of even small amount of impurities(salts and minerals) makes water a good conductor as it contains ions through which conduction takes place.
Hence water from taps, wells, lakes, etc. conduct electricity as they contain impurities.
Most liquids that conduct electricity are solutions of acids, bases and salts.
When electricity is passed through a conducting solution, the molecules of the solution dissociate into ions.
Ions are atoms or group of atoms with a positive or a negative charge.
These ions cause electrical conduction through the liquid.
Electrolyte: A liquid That conducts electricity is called an electrolyte.
Electrolysis: The process of chemical decomposition compound in a solution when an electric current passes through it is called electrolysis.
Electrolysis, is due to the chemical effect of electric current.
electrolytic cell: Two electrodes are inserted in the solution and are connected to the terminals of a battery with a switch in between them.
This arrangement is called an electrolytic cell.
anode: The electrode that is connected to the positive terminal of the battery is called the anode,
cathode: The electrode that is connected to the negative terminal of the battery is called the cathode.
Electrolysis is used in refining, electroplating and extraction of metals from impure samples.
electrorefining: This process of refining and extraction of metals from impure samples is called electrorefining.
electroplating: electroplating is the process of coating a useful metal with another metal.
chemicaleffect of electric current: The process of passing an electric current through a conducting solution to cause chemical reactions is known as the chemicaleffect of electric current.
Chemical effects of electric current: (i) Formation of bubbles of a gas on the electrodes.
(ii) Deposition of metal on electrodes.
(iii) Change in colour of solutions. Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. The object to be electroplated is made the cathode (negative electrode) by connecting it to thenegative terminal of the battery.
The metal which has to be deposited is made the anode (positive electrode) by connecting it to the positive terminal of the battery. Usually a salt solution of the metal to be coated is made as anode.
Application of Electroplating: (i) Metals that rust are often coated with other metals to prevent rusting.
(ii) Chromium plating is found on bath taps, car bumpers, etc. to give a bright attractive appearance and resist scratches and wear.
(iii) Silver plating is done on cutlery and jewellery items.
(iv) Tin cans, used for storing food, are made by electroplating tin onto iron.
Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.
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Some objects can be charged by rubbing with other objects. There are two kinds of charges — positive charge and negative charge Like charges repel and unlike charges attract each other.
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Static Electric Charges: The electric charges produced due to rubbing are called static electric charges. The electric charges constitute electric current during their motion.
An electroscope may be used to detect whether a body is charged or not.
An electroscope is a deviced used to detect the presence of electric charge.
earthing: The process of transfer of charge from a charged object to the earth is called earthing.
Lightning
Lightning is a sudden, natural and violent phenomenon of creating bright flashes during a thunderstorm.
Lightning occurs due to a high-voltage electric discharge between two clouds or a cloud and the ground, or within a single cloud during a thunderstorm.
The formation of clouds involves friction between water droplets in the atmosphere.
The friction charges the particles in the atmosphere. The negative charges accumulate at the bottom of the cloud and the positive charges at the top.
As the accumulation of the charges increases, the cloud will induce positive charges on the ground nearby.
As the amount of charge increases. This causes an imbalance of charges between a region of a cloud and gorund or another cloud (or in a cloud itself). This imbalance is significant enough to break through air resistance.
Lightning releases an average of one gigajoule of energy.
Lightning strike could destroy life and property.
Protective measures are of utmost importance during lightning strikes.
Taking shelter in interiors (house or other closed places) and vehicles (closed e.g. cars) are the most preferred measures.
Lightning conductors can protect buildings from the effects of lightning.
Earth Quake
A natural phenomenon that cannot be predicted is an earthquake.
The earth consists of three major layers, called the crust, the mantle and the core.
The core is further divided into the inner core and the outer core.
The mantle consists of semi-solid material above which the crust floats.
The crust consists of oceans and continents.
The crust is divided into several parts, called tectonic plates.
The regions where one tectonic plate slides against another are referred to as fault zones, and these are the regions where an earthquake is likely to occur.
Hence, these zones are referred to as seismic zones.
The place in the interior of the earth where an earthquake occurs is the focus, and the region on the surface of the earth that is the closest to focus is likely to experience the largest damage.
This region is called the epicenter of the earthquake.
The instrument that measures the severity of an earthquake is a seismograph.
It basically consists of a drum that rolls and a pendulum with a stylus that traces the waves of an earthquake on a sheet like a graph paper.
The energy released at the focus propagates outwardly in form of waves known as seismic waves. Destructive energy of an earthquake is measured on the Richter scale.
It is a logarithmic scale, ranging from 1 to 10 for indicating the intensity of an earthquake.
The earthquake measuring 7 or more on Richter scale can cause severe damage to life and property. Protective measures for earthquake:
If you are at home: Take shelter under a table and stay there till shaking stops.Stay away from tall and heavy objects that may fall on you. If you are in bed, do not get up. Protect your head with a pillow.
If you are outdoors: Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground. If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out till the tremors stop. Moreover, it is advisable to make the structure of buildings simple so that they are ‘Quake Safe’.
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In order to provide food for a large population – regular production, proper management and distribution of food is necessary. (Scroll down to continue …)
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Crop : When plants of the same kind are grown and cultivated at one place on a large scale, it is called a crop.
In India, crops can be broadly categorised into two types based on seasons – Rabi and Kharif crops. Sowing of seeds at appropriate depths and distances gives good yield.
Good variety of seeds are sown after selection of healthy seeds.
Sowing is done by seed drills.
Soil needs replenishment and enrichment through the use of organic manure introduction of new crop varieties.
Basic practices of crop production: (i) Preparation of Soil: One of the most important tasks in agriculture is to turn the soil and loosen it.
The process of loosening and turning of the soil is called tilling or ploughing.
(ii) Sowing: Sowing of seeds at appropriate depths and distances gives good yield.
Good variety of seeds is sown after selection of healthy seeds. Sowing is done by seed drills.
(iii) Adding Manure and Fertilisers Soil needs replenishment and enrichment through the use of organic manure and fertilisers.
Use of chemical fertilisers
fertilisers has increased tremendously with the introduction of new crop varieties.
Fertiliser: The inorganic compounds containing nutrients such as nitrogen, potassium and phosphorus. They are made in the factories.
Example: ammonium sulphate, potash, etc.
Manure: A natural substance prepared from decomposition of plant and animal wastes (cow dung, animal bones, dead leaves, dead insects and vegetable wastes) by t(he action of microbes.
iv) Irrigation : Supply of water to crops at appropriate intervals is called irrigation. Method of Irrigation: (a)Tradition methods of Irrigation: Moat, Chain pump, Dheki, Rahat.
(b) Modern methods of Irrigation: Sprinkler system, Drip
(v) Protection from Weeds: Weeding involves removal of unwanted and uncultivated plants called weeds.
(vi) Harvesting: Harvesting is the cutting of the mature crop manually or by machines.
(vii) Storage Proper storage of grains is necessary to protect them from pests and microorganisms.
Harvested food grains normally contain more moisture than required for storage.
Large scale of storage of grains is done in silos and granaries to pest like rats and insects.
Farmers store grains in jute bags or metallic bins.
Food is also obtained from animals for which animals are reared.
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Micro-organisms: Micro-organisms are too small and are not visible to the un aided eye.
They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.
They are also found inside the bodies of animals including humans. (Scroll down to continue …)
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Micro-organisms are found in air, water and in the bodies of plants and animals.They may be unicellular or multicellular.
Micro-organisms are classified into four major groups. These groups are bacteria,fungi, protozoa and some algae.
Viruses are quite different from other micro-organisms. They reproduce only inside
Micro-organisms: Friend and Foe
Based on the significance, micro-organisms can be useful or harmful.
Uses Of Microorganisms
Protozoan cause serious diseases like dysentery and malaria.
Some bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into nitrogenous compounds.
Certain bacteria convert compounds of nitrogen present in the soil into nitrogen gas which is released to the atmosphere.
Pathogens: Some of the microorganisms cause diseases animals. Such disease causing microorganisms are called pathogens.
Cleaning of Environment: The microorganisms decompose dead organic waste of plants and animals converting them into simple substances. These substances are again used by other plants and animals.
Microorganisms can be used to degrade theharmful and smelly substances and thereby clean up the environment.
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Motion: An object is said to be in motion when its position changes with respect to the reference point with time.
Rest: An object is said to be at rest when its position does not change with respect to a reference point with time.
Reference Point:
A specific point with respect to which we describe the location of an object is called a reference point.
A body can be at rest as well as in motion at the same time with respect to two different reference points.
Therefore, Rest and Motion are relative terms not absolute terms.
Rest and Motion are relative tems. Since a body may be at rest relative to one object and simultaneously it may be in motion relative to another object.
Example: a passenger sitting in a moving vehicle is at rest with respect to his fellow passenger but he is in motion with respect to a place outside the bus.
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Distance and Displacement
Distance:The total length of path covered by an object is said to be the distance travelled by it.
Displacement: Gap between the initial and final positions of an object is said to be its displacement. Or
The length of a line segment that joins the initial and final positions of an object is known as the displacement.
Difference Between Displacement and Displacement
Distance
Displacement
Distance is defined as the total length of the path travelled by an object to go from one point to another.
Displacement is defined as the length of the line segment that joins the initial and final positions of an object.
Since distance has only magnitude and its direction cannot be specified always, it is a scalar quantity.
Since displacement has magnitude and it is specified in a direction from initial position to final position, it is a vector quantity.
Distance can only have positive values.
Displacement can have both positive and negative values.
Distance depends on the length of the path travelled.
Displacement depends only on the initial and final point regardless of the path travelled.
Difference Between Displacement and Displacement
Speed And Velocity
Speed:
Speed or Average Speed: The distance travelled by an object in unit time is referred to as speed.
Its S.I unit is m/s.
In general speed refers to average speed.
For non-uniform motion, the average speed of an object is obtained by dividing the total distance travelled by an object with the total time taken.
Instantaneous Speed:
Speed of a body at an instant, that is at a very short span is known as Instantaneous Speed.
For a uniform motion, the average speed of an object is equal to its instantaneous speed throughout the path.
Velocity
Velocity Or Average Velocity:
In case of a uniform motion in a straight path, the average velocity is equal to its instantaneous velocity throughout its path.
Velocity (average velocity) of an object is equal to the instantaneous velocity of an object.
Differences Between Speed And Velocity
SPEED
VELOCITY
It is defined as the distance covered by a body per unit time.
In other words, it is the rate of change of distance.
It is defined as the Net Displacement of a body per unit time In other words, it defined as the rate of change of net displacement.
It is a scalar quantity.
It is a vector quantity.
It can never be negative or zero.
It can be negative,zero or positive.
Velocity is directed speed.
Speed may or may not be equal to velocity.
A body may possess different velocities at different positions, but the same speed.
For a moving body speed never decreases with time for a moving body.
For a moving body velocity can decrease or increase.
In case of a moving body, speed never become zero.
In case of a moving body, Velocity can be zero.
Speed in SI is measured in ms-1
Velocity in SI, is measured in ms-1
Differences Between Speed and Velocity
Uniform And Non-Uniform motion
Uniform motion or non accelerated motion: When an object covers equal distances in equal intervals of time, it is said to be in uniform motion. Uniform motion is a non-accelerated motion.
Non-uniform motion or accelerated motion: Motions where objects cover unequal distances in equal intervals of time. Uniform motion is an accelerated motion.
Acceleration
Acceleration: Change in the velocity of an object per unit time.
Graphical representation of motions
(i) Distance-time graph
For a distance-time graph, time is taken on x-axis and distance is taken on the y-axis.
[Note: All independent quantities are taken along the x-axis and dependent quantities are taken along the y-axis.]
(ii)Velocity-time graph
Equation of motion by graphical methods
Derivation Of Equations Of Motion
Equations of motion can be derived by two methods. They are (i) Graphical Method. (ii) Algebraic Method
Derivation of The Equations of Motion By Algebraic Method:
(a) Velocity-time relation:
Derivation of S = ut + ½ at2
(ii) The equation for position-time relation:
Derivation of v2 – u2 = 2as
(iii) Equation for position-velocity relation:
Conclusions From a Distance – Time Graph
Uniform Circular Motion
When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.
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We push or pull to open a door. (Scroll down to continue …)
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Effects of Force
Force can change the shape and size of an object.
Force can move a stationary object.
Force can change the speed of a body.
Force can stop a moving body.
Force can change the direction of a moving object.
Net or Resultant Force:
Resultant Force or Net Force acts on a body if two or more forces act on it at the same time. Resultant Force or Net Force on a body is defined as the net effective force due to the multiple forces acting on it simultaneously.
Based on Net force, Forces are classified into two types as:
(A) Balanced forces
(B) Unbalanced forces
(A) Balanced Forces
• If the resultant of applied forces is equal to zero, the forces are called balanced forces.
• Balanced forces do not cause any change in state of an object.
• Balanced forces can change the shape and size of an object.
For example, when forces are applied from both sides over a balloon, the size and shape of the balloon is changed.
(B) Unbalanced Forces
• If the resultant of applied forces are greater than zero, the forces are called unbalanced forces.
• Unbalanced forces can do the following :
* Move a stationary object
* Increase the speed of a moving object
* Decrease the speed of a moving object
* Stop a moving object
* Change the shape and size of an object
Laws of Motion :
Galileo Galilei :
Galileo Galilei was the first to say that objects move with a constant speed when no forces act on them.
That is, if there is no unbalanced force acting on the object, the object moves forever with a constant speed without changing its direction.
In other words, if an object is moving on a frictionless path and no other force is acting upon it, the object moves forever with a constant speed without changing its direction.
Galileo’s Experiment:
Galileo’s thought experiment considered rolling balls on inclined planes in the absence of friction or other resistant forces.
Galileo arranged two inclined planes opposite to each other as shown.
He rolls down the ball from the first inclined plane to climb the second inclined plane.
Galileo observations:
Galileo observed that:
The ball rolling down the first inclined plane comes to rest after climbing a certain height on the second inclined plane.
The speed acquired by the ball moving down a plane from a height is sufficient to enable it to reach the same height when climbing up another plane at a different inclination .
As the angle decreases, the body should travel a greater distance.
From these observations, Galileo hypothesized as:
if the force acting on the ball is only gravitational force, the height reached by the ball must be equal to the height from which it was rolled.
When the inclinations of the two planes are the same, the distance travelled by the sphere while rolling down is equal to the distance travelled by it while climbing up.
Now, if the inclination of the second plane is decreased slowly, then the sphere needs to travel over longer distances to reach the same height.
If the second plane is made horizontal, then the sphere must travel forever trying to reach the required height.
This is the case when there is no unbalanced force acting on it.
From his experiments Galileo proposed that the body could travel indefinitely far as , contrary to the Aristotelian notion of the natural tendency of an object to remain at rest unless acted upon by an external force.
Therefore, Galileo can be credited with introducing the concept of inertia, later exploited by Newton.
However, in reality, frictional forces bring the sphere to rest after it travels over a finite distance.
After further study, Newton, in his first law of motion, stated that all objects resist a change in their natural state of motion.
This tendency of resisting any change in the natural state of motion is called “inertia”.
Newton’s Laws of Motion:
Newton studied the ideas of Galileo and gave the three laws of motion. These laws are popular as Newton’s laws of motion.
Newton’s First Law of Motion (Law of Inertia):
Any object remains in the state of rest or in the state of uniform motion along a straight line, until it is compelled to change its state by applying an external force.
Newton’s First Law of Motion in Everyday Life:
(a) A person standing in a bus falls backward when the bus starts suddenly.
This happens because the person and bus both are at rest while the bus is not moving, but as the bus starts moving, an external force is acted by the bus on the legs of the person. This external force moves legs along with the bus. But the rest of his body has the tendency to remain in rest known as inertia of rest. Because of this, the person falls backward; if he is not alert.
(b) A person standing in a moving bus falls forward if the driver applies brakes suddenly. This happens because when the bus is moving, the person standing in it is also in motion along with the bus. But when the driver applies brakes the speed of the bus decreases suddenly or the bus comes to a state of rest suddenly, in this condition the legs of the person which are in contact with the bus come to rest while the rest of his body have the tendency to remain in motion. Because this person falls forward if he is not alert.
(c) Before hanging the wet clothes over the laundry line, usually many jerks are given to the clothes to get them dried quickly. Because of jerks, droplets of water from the pores of the cloth fall on the ground and the reduced amount of water
in clothes dries them quickly. This happens because when suddenly clothes are made in motion by giving jerks, the water droplets in it have the tendency to remain in rest and they are separated from clothes and fall on the ground.
(d) When the pile of coins on the carrom-board is hit by a striker, the coin only at the bottom moves away leaving the rest of the pile of coins at the same place. This happens because when the pile is struck with a striker, the coin at
the bottom comes in motion while rest of the coin in the pile has the tendency to remain in the rest and they vertically falls the carrom-board
and remain at the same place.
Momentum
Momentum of an object at state of rest is zero :
Let an object with mass ‘m’ be at rest.
Since, object is at rest, its velocity, v = 0
We know that
Momentum, p is equal to the product of mass, m and velocity, v = 0
⇒ p = m × 0 = 0
Thus, the momentum of an object in the rest i.e., non-moving, is equal to zero.
Unit of momentum :
SI unit of mass = kg
SI unit of velocity = meter per second i.e., m/s
We know that Momentum (p) = m × v
⇒ p = kg × m/s
Or ⇒ p = kg m/s
Therefore, SI unit of momentum = kg m/s
Impulse and Impulsive Force
If a cricketer catches a ball he moves his hand back while catching the ball. He does this to reduce the impact, due to the force of the ball on his hand. An object in motion has momentum. Momentum is defined as the product of mass and velocity of an object.
The momentum of the object at the starting of the time interval is called the initial momentum and the momentum of the object at the end of the time interval is called the final momentum. The rate of change of momentum of an object is directly proportional to the applied force.
Newton’s second law quantifies the force on an object. The magnitude of force is given by the equation,
F = ma, where ‘m’ is the mass of the object and ‘a’ is its acceleration. The CGS unit of force is dyne and the SI unit is newton (N).
A large amount of force acting on an object for a short interval of time is called impulse or impulsive force. Numerically impulse is the product of force and time. Impulse of an object is equal to the change in momentum of the object.
Impulse and Impulsive Force
The momentum of an object is the product of its mass and velocity. The force acting on a body causes a change in its momentum. In fact, according to Newton’s second law of motion, the rate of change in the momentum of a body is equal to the net external force acting on it.
Another useful quantity that we come across is “impulse”. “Impulse” is the product of the net external force acting on a body and the time for which the force is acted.
If a force “F” acts on a body for “t” seconds, then Impulse I = Ft.
In fact, this is also equal to the change in the momentum of the body. It means that due to the application of force, if the momentum of a body changes from “P” to “P ‘ ”, then impulse,I = P ‘ – P.
For the same change in momentum, a small force can be made to act for a long period of time, or a large force can be made to act for a short period of time. A fielder in a cricket match uses the first method while catching the ball. He pulls his hand down along with the ball to decrease the impact of the ball on his hands.
In a cricket match, when a batsman hits a ball for a six, he applies a large force on the ball for a very short duration. Such large forces acting for a short time and producing a definite change in momentum are called “impulsive forces”.
Newton’s Second Law of Motion
Newton’s Second Law of Motion states that, the rate of change in momentum of an object is proportional to applied unbalanced force in the direction of force.
Mathematical expression:
State and derive newton’s second law of Motion
Statement: Newton’s second law of motion states that the rate of change of momentum of an object is Proportional to the applied unbalanced force in the direction of force.
Derivation of Newton’s second law of motion:
Suppose an object of mass, m is moving along a straight line with an initial velocity, u.
It is uniformly accelerated to velocity, v in time, t by the application of a constant force, F throughout the time t.
⇒Initial momentum of the object, p1 = mu
⇒Final momentum, p2 = mv
⇒Change in momentum = p2 – p1
⇒The change in momentum = mv – mu
⇒The change in momentum = m × (v – u)
⇒The rate of change of momentum = m(v -u)t
⇒ m (v -u)t
According to Newton’s Second Law of Motion,
Applied force α Rate of change in motion
⇒ F m (v -u)t
F=km (v -u)t = kma —————————- (i)
Here, k is a constant of proportionality and
(v -u)t is the rate of change of velocity, which equals acceleration, a.
The SI units of mass and acceleration are kg and m s-2 respectively.
The unit of force is so chosen that the value of the constant, K becomes one For this.
One unit of force is defined as the amount that produces acceleration
of 1 m s-2 in an object of 1 kg mass.
That is,
1 unit of force = k × (1 kg) × (1 m s-2).
Thus, the value of k becomes 1. From Eq. (iii)
F = ma ————————————-
The unit of force is kg m s-2 or newton, with the symbol N.
Newton’s Third Law of Motion
To every action there is an equal and opposite reaction.
Applications:
(i) Walking is enabled by 3rd law.
(ii) A boat moves back when we deboard it.
(iii) A gun recoils.
Rowing of a boat.
Law of Conservation of Momentum
Law of conservation of momentum states that, if two or more bodies collide, the sum of the initial momentum is equal to the sum of the final momentum.
Or
Law of conservation of momentum states that the sum (total) of the individual momentums of the colliding bodies just before the collision is equal to the sum (total) of the individual momentums of the colliding bodies after the collision
Derivation of Law of Conservation of Momentum From Newton’s Third Law of Motion.
Answer:
For a system of bodies ( two or more bodies ), the total vector sum of momenta of all the bodies due to the mutual action and reaction remain unchanged as long as no external force is acted on the system.
Consider two bodies A and B of the masses m1, m2 moving with the initial velocities u1, u2 respectively.
For a system, let, these masses collide and their velocities after collision are v1, v2 respectively.
If ‘A’ applies a F on B for a time, t;
‘B’ applies a force –F on A for time t [according to Newton’s third law of motion].
Then,
[]
Therefore, the sum of momentum before impact is equal to the sum of the momenta after the impact represents the law of conservation of momentum.
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