Category: CBSE Class 8

On this page, you will find Fractions and Decimals Class 7 Notes Maths Chapter 2 Pdf free download. CBSE NCERT Class 7 Maths Notes Chapter 2 Integers will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Maths Chapter 2 Notes Fractions and Decimals

Fractions and Decimals Class 7 Notes Conceptual Facts

Fraction \(=\frac{\text { Numerator }}{\text { Denominator }}\)

1. Types of fraction:

• Proper fractions = Representing a part of a whole, e.g\(\frac{1}{2}, \frac{3}{4} \text { and } \frac{1}{4}\)
• Improper fraction: Numerator is always greater than the denominator, \(\text { e.g. } \frac{6}{5}, \frac{7}{4} \text { and } \frac{3}{2}\)
• Mixed fraction: Combination of a whole number and a proper fraction.\(\text { -e.g. } 1 \frac{2}{3}, 2 \frac{5}{6} \text { and } 3 \frac{1}{2}\)

2. Multiplication of two fractions: \(\frac{\text { Product of numerators }}{\text { Product of denominators }} \text { e.g. } \frac{2}{5} \times \frac{3}{4}=\frac{2 \times 3}{5 \times 4}=\frac{6}{20}\)

3. Reciprocal of a non-zero fraction is obtained by interchanging its numerator and the denominator e.g. reciprocal of  \(\frac{3}{4} \text { is } \frac{4}{3}\)

4. While dividing a whole number by a fraction, we multiply the whole number with the reciprocal of that
\(\text { e.g. } 5 \div \frac{3}{2}=5 \times \frac{2}{3}=\frac{10}{3}\)

5. While dividing a fraction by a whole number, we multiply the fractions by the reciprocal of the whole
\(\text { e.g. } \frac{1}{4} \div 2=\frac{1}{4} \times \frac{1}{2}=\frac{1}{8}\)

6. Division of a fraction by another fractions.

7. Multiplication of two decimal numbers: 2.25 x 1.2 = 2.700

8. Number obtained by dividing a non-zero integer by 0, is not defined, e.g. \(\text { e.g. } \frac{2}{0}, \frac{\frac{3}{2}}{0} \text { and } \frac{-5}{0}\)

On this page, you will find Integers Class 7 Notes Maths Chapter 1 Pdf free download. CBSE NCERT Class 7 Maths Notes Chapter 1 Integers will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Maths Chapter 1 Notes Integers

Integers Class 7 Notes Conceptual Facts

1. Number line

For a positive integer on number line, we move towards right of zero and for a negative integer, we move towards the left of the zero.

2. Integers are closed under addition, subtraction and multiplication.
For example:

• a + b = integer
• a – b = integer
• a x b = integer

3. Addition and multiplication are cumulative for integers.
For example:

• a + b = b + a
• a x b = b x a

4. Addition and multiplication are associative for integers.
For example:

• (a + b) + c = a + (b + c)
• (a x b) x c = a x (b x c)

5. Zero (0) is an additive identity for integers.
For example: a + 0 = 0 + a = a

6. One (1) is a multiplicative identity for integers.
For example: a x 1 = 1 x a = a

7. Algebra of integers,

• a x (-b) = -ab
• (-a) xb = -ab
• (-a) x (-b) = ab
• a xb = ab

8. Product of even number of negative integers is positive whereas the product of odd number of negative integers is negative. For example:

• (-a) x (-b) x (-c) x (-d) (-e) -a x b x c x d x e …. even number times
• (-a) x (-b) x (-c) x (-d) (-e) = -(a x b x c x d x e) odd number times

9. Division on integers:
(i) \(\frac{(-a)}{(b)}=-\left(\frac{a}{b}\right)\)
(ii) \(\frac{(-a)}{(-b)}=\left(\frac{a}{b}\right)\)
(iii) \(\frac{(a)}{(-b)}=-\left(\frac{a}{b}\right)\)
(iv) \(\left(\frac{+a}{+b}\right)=\left(\frac{a}{b}\right)\)

 

On this page, you will find Pollution of Air and Water Class 8 Notes Science Chapter 18 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 18 Pollution of Air and Water will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 18 Pollution of Air and Water

Pollution of Air and Water Class 8 Notes Understanding the Lesson

1. Agents or substances that pollute water, air or soil are called pollutants.

2. The term air pollution is defined as the accumulation of harmful substances or increase in the quantity of any gas in the air above the normal level.

3. Air pollution is harmful for human beings also.

4. In the earth’s atmosphere there is about 78% of nitrogen, 21% of oxygen and the rest are other gases like CO₂, methane, ozone and water vapour.

5. The substances which contaminate the air are called air pollutants.

6. There are natural as well as man-made sources of air pollution.

7. Smoke and fog combines to form smog. Smoke may contain oxides of nitrogen which combine with other pollutants and fog to form smog.

8. Smog causes breathing difficulties.

9. Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays damages ozone layer of the atmosphere.

10. Some pollutants like SO₂ and NO₂ react with water vapour present in the air to form sulphuric acid and nitric acid. These acids come down with rain as acid rain.

11. A part of the radiation of the sun that falls on the earth is absorbed by it, whereas a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. This trapping of radiations by the earth’s atmosphere causes warming of the earth and this is known as greenhouse effect.

12. Human activities contribute to the accumulation of CO₂ in the atmosphere. CO₂ traps heat and does not allow it to escape into space. As a result of this, the average temperature of the earth’s atmosphere increases gradually and this is called global warming.

13. Gases which contribute to global warming, like CO₂, methane, nitrous oxide and water vapour are called greenh’ouse gases.

14. The substances that pollute water are called water pollutants.

15. The harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water and this leads to water pollution.

16. Water which is suitable for drinking is called potable water.

17. Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets ‘ or bleaching powder to the water.

18. We must conserve water as it is a precious natural resource.

Class 8 Science Chapter 18 Notes Important Terms

Air pollution: When some unwanted substances get mixed with air and have harmful effect on both living and non-living things, is known as air pollution.

Chemical contamination: Presence of harmful chemicals in air, water and soil causing pollution of water is called chemical contamination.

Global warming: Due to the increasing levels of greenhouse gases, like CO₂, the average temperature of earth’s atmosphere is gradually increasing. This is called global warming.

Greenhouse effect: The process of trapping of radiations by the Earth’s atmosphere due to increasing levels of gases like CO₂ is called greenhouse effect.

Pollutants: The substances which causes pollution are known as pollutants.

Potable water: Water which is purified and is also fit for drinking is known as potable water.

Water pollution: The contamination of clean water by substances which are harmful to life is called water pollution.

On this page, you will find Stars and the Solar System Class 8 Notes Science Chapter 17 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 17 Stars and the Solar System will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 17 Stars and the Solar System

Stars and the Solar System Class 8 Notes Understanding the Lesson

1. The science dealing with the study of the universe is called astronomy.

2. The scientist who study the universe are called astronomers.

3. The stars, the planets, the moon and many other objects in the sky are called celestial objects.

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

5. The phases of the moon occur because we can see only that part of the moon which reflects the light of the sun towards us.

6. The stars are hot glowing spheres that continuously emit their own heat and light, that is they are self luminous objects.

7. Stars appear to move from east to west.

8. The group of stars that move together and form a characteristic pattern in the sky is called constellation.

9. There are many types of constellations like Ursa Major, Ursa Minor, Orion.

10. The sun and the celestial bodies which revolve around it form the solar system. It consists of large number of bodies such as planets, comets, asteroids and meteors.

11. The sun is the nearest star from us. It continuously emits huge amounts of heat and light.

12. A planet has a definite path in which it revolves around the sun. This path is called orbit.

13. There are total eight planets in our solar system.

14. There is a large gap in between the orbits of Mars and Jupiter. This gap is occupied by a large number of small objects that revolve around the sun. These are called asteroids.

15. Comets are also members of our solar system. They revolve around the sun, in highly elliptical orbits. A comet appears generally as a bright head with a long tail.

16. Meteors are the pieces made of stones or metals or both that move very fast in space. They are also called as ‘shooting stars’.

17. Some meteors are so big in size that they do not burn up completely in the atmosphere and reach the earth’s surface. They are called meteorites.

18. A satellite is defined as a heavenly body that moves around another heavenly body along its own orbit.

19. There are two types of satellites:

• Natural satellite
• Artificial satellite

20. Aryabhatta was the first Indian satellite. Some other Indian satellites are INSAT, IRS, Kalpana, EDUSAT, etc.

21. Artificial satellites have many practical applications. They are used for forecasting weather, transmitting television and radio signals. They are used for telecommunication and remote sensing.

Class 8 Science Chapter 17 Notes Important Terms

Artificial satellite: The satellites other than natural satellites are known as artificial satellites. They are used for forecasting weather, transmitting television and radio signals.

Asteroids: Asteroids are small bodies revolving around the sun mostly between the orbits of Mars and Jupiter.

Cassiopeia: Cassiopeia is another prominent constellation in the northern sky. It is visible during winter in the early part on the night.

Celestial objects: Objects such as stars, the planets, the moon and many other objects in the sky are called celestial objects.

Comets: Comets are small, icy objects that orbits the sun and has a long tail of gas. They revolve around the sun in highly elliptical orbits.

Constellations: The group of stars that move together and form a characteristic pattern in the sky are called constellations.

Light year: The distance travelled by light in one year is known as light year.

Meteorites: Some meteors are so large that a part of them reaches the surface of the Earth before they evaporate completely. These are called meteorites.

Meteors: A meteor is a small heavenly object moving around the sun. When a meteor occasionally enters the Earth’s atmosphere it gets heated up because of friction and glows but evaporates in a very short period of time.

Natural satellites: A natural celestial body revolving around another celestial body is called natural satellites.

Orbit: A planet revolves around the sun in a definite path. This path is known as orbit of the planet.

Orion: Orion is a constellation which contain 7 or 8 stars. It looks like a hunter.

Phases of Moon: The various shapes of the bright part of the moon as it is seen during a month are called phases of moon.

Planets: The celestial bodies that revolve around the sun in a well defined orbit are known as planets.

Pole star: The only star which always appears to remain at the same position in the sky is known as pole star.

Remote sensing: It is scanning of the earth by artificial satellite for collecting information from distance.

Solar system: The sun and the celestial bodies which revolve in the space form the solar system.

Stars: Stars are the celestial bodies which emit light of their own. The sun is also a star.

Ursa Major: Ursa major is a constellation which constitutes seven stars and is also known as ‘SaptarishV.

On this page, you will find Light Class 8 Notes Science Chapter 16 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 16 Light will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 16 Light

Light Class 8 Notes Understanding the Lesson

1. Light is a form of energy.

2. When light reaches our eyes after striking an object, we are able to see an object.

3. The bouncing back of light into the same medium after it falls on a surface is called reflection.

4. The ray of light striking the surface is called an incident ray.

5. The ray of light which is returned back into the same medium is known as the reflected ray.

7. The perpendicular drawn to the reflecting surface at the point where incident ray strikes the mirror is called normal.

8. The angle between the incident ray and the normal is called the angle of incidence.

9. The angle between the reflected ray and the normal is called the angle, of reflection.

10. Laws of reflection:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, the reflected ray and the normal all lie in the same plane.

 

 

11. When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as irregular reflection.

12. The reflection of light from a smooth and polished surface is known as regular reflection.

13. Two mirrors inclined to each other give multiple images.

14. Kaleidoscope is a device based on the principle of multiple reflections.

15. Sunlight is referred to as white light which consists of seven colours.

16. Splitting of white light into its constituent colours is called dispersion.

15. The human eye is an important sense organ that enables us to see the world around us. It is nearly spheri¬cal in shape.

16. Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.

17. Blind spot is a portion on the retina where the nerve fibres enter the optic nerve. The image falling on the portion can’t be seen.

18. A normal eye can see nearby and distant objects clearly.

19. Long-sightedness or hypermetropia is a defect of the eye where the person cannot clearly see the nearby objects while in short-sightedness or myopia, the far-away objects can not be seen clearly. Visually challenged persons can read and write using the Braille system.

20. Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

Class 8 Science Chapter 16 Notes Important Terms

Angle of incidence: The angle between the incident ray and the normal is called the angle of incidence.

Angle of reflection: The angle between the reflected ray and the normal is called the angle of reflection.

felind spot: The portion on the retina where the nerve fibres enter the optic nerve is called blind spot. The image falling on this portion can’t be seen.

Braille: The system of representing characters by raised dots which enables the blind person to read is called Braille.

Cones: Visual receptor cells in retina, which are sensitive to bright light and sense colour are called cones.

Cornea: The transparent front part of the eye is called cornea.

Diffused/Irregular reflection: When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as irregular/diffused reflection.

Dispersion: The splitting of light into its constituent colours is known as dispersion.

Incident ray: The ray of light striking the surface is called as incident ray.

Iris: The dark muscular structure behind the cornea is called iris.

Kaleidoscope: A device based on the principle of multiple reflections is called kaleidoscope.

Lateral inversion: The phenomenon of changing side, i.e, left to right and right to left by the mirror while forming an image is called lateral inversion.

Pupil: The small opening in the cornea is called pupil.

Reflected rays: The rays of light which returns back from the surface after reflection is known as refl ected ray.

Reflection: The bouncing back of light into the same medium after it falls on a surfac is called reflection.

Regular reflection: When all the parallel rays reflected from a smooth and polished surface is also parallel is called regular reflection.

Retina: The site where the image is formed in the eye is called retina.

Rods: The nerve cells on retina which are sensitive to dim light are called rods.

On this page, you will find Some Natural Phenomena Class 8 Notes Science Chapter 15 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 15 Some Natural Phenomena will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 15 Some Natural Phenomena

Some Natural Phenomena Class 8 Notes Understanding the Lesson

1. Lightning is an electric spark on a huge scale. It is caused by the accumulation of charges in the clouds.

2. Some objects can be charged by rubbing with other objects. These objects are called charged objects.

3. There are two types of charges – positive and negative.

4. The charge acquired by a glass rod when it is rubbed with silk is called positive.

5. The charge on an ebonite rod when rubbed with fur, wool or flannel is considered as negative.

6. The electric charges generated by rubbing are called static charges.

7. When charges move they constitute an electric current. Thus, moving charges are called current.

8. Like charges repel each other and unlike charges attract each other.

9. A device used to test whether an object is carrying charge or not is called an electroscope.

10. Electric charge can be transferred from a charged object to another through a metal conductor.

11. The process of transferring of charge from a charged object to the earth is called earthing.

12. When a body loses charges to the earth or any other it is said to be discharged.

13. The process of electric discharge between clouds and the earth or between different clouds causes lightning.

14. Lightning strike could destroy life and property. It is, therefore, necessary to take measures to protect ourselves.

15. During lightning and thunderstorm no open place is safe. A house or a building is a safe place. During travelling by car or by bus, it is safe to stay inside with windows and doors of the vehicle shut. Carrying an umbrella is not at all a good idea during thunderstorm. If in a forest, shelter should be taken under shorter trees.

16. Lightning can strike telephone cords, electrical wires and metal pipes. Electrical appliances like computer, TV, etc., should be unplugged. Electrical lights can remain on.

17. Lightning conductor is a device used to protect buildings from the effect of lightning.

18. An earthquake is a sudden shaking or trembling of the earth. It lasts for a very short time. It is caused by a disturbance deep inside the earth’s crust.

19. Earthquake can cause a great loss to our life and property. It can cause immense damage to buildings, bridges, dams and people. It can also cause floods, landslides and tsunamis.

20. Unfortunately, we are not yet able to predict an earthquake accurately.

21. The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.

22. Earthquakes having magnitudes higher than 7 on the Richter scale cause a great destruction to our life and property.

23. Earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are known as seismic or fault zones.

24. We should adopt precautionary and protective measures to save ourselves from the upcoming damages of an earthquake.

Class 8 Science Chapter 15 Notes Important Terms

Crust: The uppermost layer of Earth’s surface (8 km – 32 km) is termed as crust.

Discharge: Discharge is the release or transmission of charges from one object to another through a medium like liquid, gas or solid.

Earth’s plates: The outermost layer of the earth is fragmented. Each fragment is called a plate.

Earthquake: An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by deep disturbances caused by movement of earth’s plates inside the earth’s crust.

Electroscope: It is a device used to test whether an object is charged or not.

Lightning: It is the process of electric discharge between cloud and the earth or between different clouds.

Lightning conductor: It is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed on the roof of elevated structure.

Negative charge: The charge of an object due to excess of electrons is called negative charge.

Positive charge: The charge of an object due to loss of electrons is called positive charge.

Richter scale: The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale.

Seismograph: It is an instrument which measures and records the magnitude of an earthquake in terms of the shock waves it produces.

Thunder: The loud noise accompanied by lightning is called thunder.

Thunderstorm: A storm accompanied by thunder and lightning is called thunderstorm.

Transfer of charge: Electric charges can be transferred from a charged object to another through a metal conductor.

Tsunami: A sudden violent change in the earth’s surface resulting from a destructive sea wave caused by an earthquake or volcanic eruption is known as tsunami. Coastal areas around the ocean suffer huge Mosses.

Tremor: A small earthquake is called tremor.

On this page, you will find Sound Class 8 Notes Science Chapter 13 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 13 Sound will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 13 Notes Sound

Sound Class 8 Notes Understanding the Lesson

1. Sound is defined as a form of energy that travels through medium in the form of vibrations.

2. A sound can be produced by:

• beating
• rubbing
• blowing
• plucking

3. The movement that produces sound in rapid to and fro motion is called vibration.

4. Sound requires medium to travel. Sound can travel through solids, liquids and gases but not through vacuum.

5. Sound travel fastest in solid and slowest in gases.

6. In human beings, the sound is produced by the voice box or the larynx.

7. Voice box is located at the upper end of the windpipe.

8. The eardrum senses the vibration of sound and sends the signal to the brain. This process is called hearing.

9. A vibration has three important characteristics – frequency, amplitude and time period.

10. Frequency is defined as the number of vibrations made by a vibrating body in one second. Its unit is hertz (Hz).

11. Amplitude is defined as the maximum extent to which a vibrating body can vibrate.

12. Time period is defined as the time taken by a vibrating body for one complete vibration.

13. Loudness is the characteristic of sound that enables us to distinguish a loud sound from low sound.

14. Pitch is a characteristic of sound that enables us to distinguish a shrill sound from the grave (hoarse) sound.

15. The term quality is defined as the characteristic of sound by virtue of which we can easily differentiate the two sounds of same pitch.

16. The unwanted and unpleasant sound that causes discomfort is called noise.

17. The sound that we enjoy from musical instruments are called musical sound.

18. Presence of excessive or unwanted sounds in the environment is called noise pollution.

19. Plantation on the roadside and elsewhere can reduce noise pollution.

Class 8 Science Chapter 13 Notes Important Terms

Amplitude: is defined as the maximum extent to which a vibrating body can vibrate.

Audible: The type of sounds which we are able to hear are called audible sounds.

Eardrum: Eardrum is a thin membrane through which the sound waves passed.

Hertz: The frequency is expressed in hertz (Hz).

Larynx: Larynx is the organ which produces sound in the human being. It is also called voice box.

Loudness: Is the characteristic of sound that enables us to distinguish a loud sound from low sound.

Noise: The sound which are unpleasant to hear are termed as noise.

Oscillation: The to and fro motion of the vibrating particles about its mean position is called oscillation.

Pitch: The characteristic of sound by which we distinguish between different sounds of the same loudness is known as pitch.

Shrillness: The property of sound that depends upon frequency of vibrating object is known as shrillness.

Time period: The time taken by the bob of the pendulum to complete one oscillation, is called its time period.

Ultrasonic sound: The sound which have frequencies greater than 20,000 Hz is called ultrasonic sound.

Vibration: The movement of a body from one extreme position to the other is termed as vibration.

Voice box: It is that part by which sound is produced in humans.

Windpipe: The pipe which connects the larynx with the lungs is called windpipe.

On this page, you will find Chemical Effects of Electric Current Class 8 Notes Science Chapter 14 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 14 Chemical Effects of Electric Current will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 14 Notes Chemical Effects of Electric Current

Chemical Effects of Electric Current Class 8 Notes Understanding the Lesson

1. The substances that allow the electric current to pass through them are called conductors; e.g., copper, aluminium, etc.

2. The substances that do not allow the electric current to pass through them are called insulators; e.g., I rubber, plastic, wood, etc.

3. Some liquids are good conductors of electricity and some are poor conductors.

4. Most liquids that conduct electricity are solutions of acids, bases and salts.

5. Pure or distilled water is free of salts and thus act as insulator or a bad conductor of electricity. Water from tap, handpumps, wells, etc., is not pure but a solution. It contains small amount of mineral salts dissolved in it. This water is thus a good conductor of electricity.

6. Common salts when dissolved in distilled water, makes it a good conductor.

7. The passage of an electric current through a conducting solution causes chemical reactions such as formation of bubbles of a gas on the electrodes, deposits of metals on the electrodes, changes of colour of solutions, etc., is known as chemical effects of current.

8. Electroplating is one of the most common application of chemical effects of current. It is the process of depositing a layer of any desired metal on another material by means of electricity.

9. Electroplating is done to make objects shiny in appearance, resistant to scratches and corrosion.

Class 8 Science Chapter 14 Notes Important Terms

Electrode: An electrode is a conductor that allows electric current to pass from one medium to another using the graphite or metal plates or rods.

Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. It is done by using an electrolytic cell.

Good conductor: The materials which allow electric current to pass through them are called good conductors of electricity; e.g., copper, aluminium, etc.

Poor conductor: The materials which do not allow electric current to pass through them are called poor or bad conductors of electricity. They are also known as insulators; e.g., rubber, plastic, wood, etc.

LED: It is an electronic device containing two wires called leads, one lead (longer) is connected to the positive (+) terminal and the other (smaller) to the negative (-) terminal of the battery. It starts emitting light even when a very weak current flows through it. It is actually Light Emitting Diode.

On this page, you will find Friction Class 8 Notes Science Chapter 12 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 12 Friction will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 12 Friction

Friction Class 8 Notes Understanding the Lesson

1. Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.

2. Friction always acts in a direction opposite to the direction of motion.

3. The force of friction always opposes the applied force. So it is defined as a force that opposes motion.

4. Friction depends upon the nature of surfaces in contact. It also depends upon the weight of the body.

5. Friction is greater in rough surface and smaller in smooth surface.

6. Friction is caused by the interlocking of irregularities between the two surfaces, Friction is independent of the area of contact.

7. Friction is both a friend and a foe. It is a necessary

8. Friction can never be reduced to zero.

9. Friction is also caused due to the force of adhesion.

10. The substances that reduce friction are known as I lubricants. They form a thin layer on the moving I surfaces. So, they do not rub directly against each other.

11. Friction can be reduced by using grease, oil, powder, ball bearings and a cushion of dry air between the 1 moving surfaces.

12. The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction. It comes into play when try to move an object at rest.

13. When one body or object rolls over the surface of another body or object, the resistance to its motion is known as rolling friction.

14. When one object slides over another object, the friction that comes into action is called sliding friction.

15. The force of friction exerted by fluids is also known as drag. The common name of gases and liquids is fluid.

16. Ball bearings are used to reduce friction.

17. Fluid friction of an object depends upon its speed with respect to the fluid, the shape of the object and the nature of the fluid.

18. A special shape is given to overcome drag of an object. For example, shape of an aeroplane and ship are streamlined. Birds and fish have naturally got such shape.

19. Sometimes we deliberately increase friction by using brake pads in the brake system of bicycles and auto¬mobiles and by grooving soles of shoes or tyres of vehicles, etc.

Class 8 Science Chapter 12 Notes Important Terms

Ball bearing: A bearing in which the parts are separated by a ring of small freely rotating metal balls.Ball bearings are used to reduce friction.

Drag: The frictional force exerted by fluids is called drag.

Fluid friction: Friction that occurs in liquids or gases is called fluid friction.

Friction: The resistance that one surface or object encounters when moving over another is known as friction. It opposes the relative motion between two surfaces in contact.

Interlocking: Irregularities in two surface may clasp with each other, resulting in their interlocking.

Lubricants: The substances that reduce friction are called lubricants.

Rolling friction: When one object rolls over another object, the resistance to its motion is called rolling friction.

Sliding friction: When one surface slides over another surface, sliding friction gets into action.

Static friction: To counter balance the applied force on the object, static friction comes into action.

On this page, you will find Force and Pressure Class 8 Notes Science Chapter 11 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 11 Force and Pressure will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 11 Force and Pressure

Force and Pressure Class 8 Notes Understanding the Lesson

1. A push or pull on an object is called force.

2. Forces applied on an object in the same direction add to one another.

3. If two forces act in the opposite directions on an object, the net force acting on it is the difference between the two forces.

4. The strength of a force is usually expressed by its magnitude.

5. Force on an object may change its state of motion, speed, direction and shape.

6. The force resulting due to the action of muscles is known as the muscular force.

7. Muscular force can only be applied when it is in contact with an object, it is also called as contact force.

8. The force responsible for changing the state of motion of an object is known as the force of friction.

9. The force exerted on an object without touching it is known as non-contact force.

10. The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.

11. The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity. This force is known as gravitational force.

12. The force acting on a unit area of a surface is called pressure.

13. The envelop of air around us is known as atmosphere.

14. The pressure exerted by the atmosphere is known as atmospheric pressure.

Class 8 Science Chapter 11 Notes Important Terms

Atmospheric pressure: The pressure exerted by air around us is termed as atmospheric pressure.

Contact force: The type of force which acts only when the object are in physical contact with each other is called contact force.

Electrostatic force: The force exerted by an electrified body is called electrostatic force.

Force: A push or pull which tends to change the state of rest, motion direction, size and shape is called as force.

Friction: The force acting between two surfaces in contact which opposes the motion of one body over the another body is called the force of friction.

Gravitational force: The force of attraction between any two objects which have mass is called gravitational force.

Gravity: The force of gravitation which acts on the bodies close to the surface of the earth is called the force of gravity of the earth.

Magnetic force: The type of force which is exerted by a magnet is called magnetic force.

Muscular force: The type of force which is exerted by the muscles of a human or animal body is called muscular force.

Non-contact force: The type of force which is exerted by a body on another body without any direct contact with it is called non-contact force.

Pressure: Force acting per unit area is called pressure.

Pull: The type of force which move the object towards source of the force.

Push: The type of force which move the object forward or away from the source of force.

On this page, you will find Reaching the Age of Adolescence Class 8 Notes Science Chapter 10 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 10 Reaching the Age of Adolescence will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 10 Reaching the Age of Adolescence

Reaching the Age of Adolescence Class 8 Notes Understanding the Lesson

1. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. It begins around the age of eleven and lasts upto eighteen or nineteen years of age. Hence adolescence occurs between childhood and adulthood.

2. The human body undergoes several changes during adolescence such as change in body shape, voice change, development of sex organs, etc.

3. The phase wherein the bodily changes occurs in terms of sexual growth, is known as puberty. Therefore puberty is defined as the onset of reproductive maturity, starting at the age of 11 years and lasts till the age of 18 years. It starts earlier in females than in males.

4. During adolescence, in girls, the region below the waist becomes wider whereas in boys, shoulders broaden and the muscles of the body grow more prominently than girls.

5. At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes and produce hoarse voice whereas girls have a high pitched or shrilled voice. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

6. There is a sudden change in height of human beings during puberty. The height increases faster in girls than boys and both reach their maximum height at the age of 18.

7. During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases which results in development of acne and pimples on the face of boys and girls.

8. In the period of adolescence, a person reaches the maturity level of mental, intellectual and emotional thinking.

9. During puberty, breasts begins to develop in girls; facial hair, i.e., moustache and beard in boys. These features which distinguish the male from female are called secondary sexual characters.

10. The changes which occur at adolescence are controlled by hormones which are chemical substances. They are secreted from endocrine glands, or endocrine system.

11. The male hormone or testosterone is released by the testes and the female hormone or estrogen is produced by ovaries are responsible for secondary sexual characters in both of them. The production of these hormones are under the control of pituitary gland.

12. Hormones from pituitary stimulate testes and ovaries to release male (testosterone) and female (estrogen) hormone into the blood stream which reach a particular body part called target site. The target site responds to the hormones. The testes and ovaries secrete sex hormones which are responsible in the male and female secondary characters.

13. Reproductive phase of life in humans start when their testes and ovaries begin to produce gametes. In male, the reproductive phase begins at puberty at the ages 14 – 15 and lasts, as long as he is healthy whereas in female it begins at the ages 10-12 and lasts until the age of 45-50 years.

14. The uterine wall in females prepare itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down along with blood. This is called menstruation.

15. The first menstrual flow begins at puberty is termed as menarche.

16. Stoppage of menstruation at the age of 45-50 is termed as menopause.

17. Sex of unborn child depends on whether the egg is fertilised with sperm having X or Y chromosome.

18. The thyroid gland produces the thyroxine hormone which prevents from ‘goitre’ disease. Similarly, the pancreas produces the insulin hormone which checks the disease ‘diabetes’. The adrenals produce hormone 1 adrenaline which helps the body to adjust to stress when one is very angry, embarrassed or worried.

19. The adrenals and thyroid secrete their hormone when they receive orders from the pituitary through its I hormones. The pituitary also secretes growth hormone which is necessary for the normal growth of a person.

20. Hormones play a vital role in completing life cycle in insects and frogs. For example, metamorphosis (changing of larva into adult) in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by thyroid. The production of thyroxine needs the presence of iodine in water.

21. Nutritional needs of the adolescents: At the stage of adolescence, the human body grows at an extremely fast rate and requires adequate intake of a balanced diet which should contain proportionate I amount of proteins, carbohydrates, fats, vitamins and minerals, etc. They can be obtained from green vegetables, normal Indian meal of roti/dal/rice, milk, fruits, etc.

21. Maintaining personal hygiene and doing physical exercise is of utmost important to stay fit and healthy.

22. We should avoid drug to avoid physical, mental and emotional ailments.

Class 8 Science Chapter 10 Notes Important Terms

Adam’s apple: At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

Adolescence: The period of life, when the body undergoes changes, which leads to reproductive maturity, is called adolescence. It starts around the age of 11 and lasts upto 18 or 19 years of age.

Adrenaline: The hormone produced by adrenals is called adrenaline. It helps the body to adjust to stress when one is very angry, embarrassed and worried.

Balanced diet: A balanced diet or meal is one which includes proteins, vitamins, fats, carbohydrates, minerals, etc., in adequate quantity and proportion.

Chromosomes: These are thread-like structures present inside the nucleus of a cell and helps in for carrying genetic information from one generation to next generation.

Endocrine glands: Different types of hormones are secreted from particular glands called endocrine glands or endocrine system.

Female hormone or estrogen: The female hormone is secreted by ovaries at the onset on puberty and causes development of secondary sexual characters in female.

Growth hormones: Pituitary gland secretes growth hormones which is necessary for the normal growth of a person.

Hormones: Hormones are chemical substances secreted from endocrine glands. They are responsible for regulating metabolic and other activities of the body.

Insulin: The hormone produced by pancreas is called insulin.

Male hormone or testosterone: The male hormone is released by the testes at the onset of puberty and causes changes in secondary sexual characters.

Menarche: The first menstrual flow begins at puberty is known as menarche.

Menopause: When the menstruation ceases, the stage is called menopause.

Menstruation: The process in a woman of discharging blood and other material from the lining of uterus at intervals of about 28-30 days is called menstruation.

Pituitary gland: A pea-sized body attached to the base of the brain that is important in controlling growth and development and functioning of the other endocrine gland.

Puberty: The period of life, during which the human body undergoes several changes and reaches sexual maturity and the human beings become capable of reproduction, is called puberty.

Reproductive health: Good health is essential for adolescence and for reproductive phase of life. For good health one should have a balanced diet, do physical exercises, avoid smoking, drinking and drugs, maintain hygiene and take proper sleep and rest.

Secondary sexual characters: In adolescence period, there are several changes including growth of facial hair, i.e., moustaches and beard on boys’ face, development of breast in girls, etc. These features or characters that help to distinguish the male from the female are called secondary sexual characters.

Sex chromosomes: All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chro-mosomes out of these are the sex chrmosomes named X and Y. A male has one X and one Y chromosome while a female has two X chromosomes.

Thyroxine: The hormone produced by the thyroid gland is called thyroxine.