class 12 physics

Class 9 Science: Chapter-Wise Detailed Explanation [Updated]

Looking for detailed explanation for class 9 science? Yes! This is the platform to learn and get your concepts clear about class 9 science.

We are here to explain theory in detail so that you can gain best knowledge to understand each concept more precisely. There are lots of new concepts in class 9 science. But, today, we will learn it and master it.

Class 9 Science will help you gain knowledge about motion, matter, atoms, tissues, living organisms, force, gravitation, work and energy, sound, natural resources and human resources.

So, let’s move inside to learn each chapter of class 9 science in more detail:-

Class 9th Science Chapter 1: Laws of Motion

We have seen a Motion of several objects everyday.  Many times we can not see the motion of an object directly, as in the case of air.  Now in this chapter will we see Motion of Object surroundings. So in 9th  standard we will see laws of motion, distance and displacement , acceleration and Newton’s laws  of motion. 

Displacement and Distance :- 

So basically what is Displacement is that if the position of an object is changing with respect to its surrounding, then it is said to be a Motion otherwise that object will be at rest.  Let’s take an example of a person who is travelling in the Bus , you can see the person sitting next to him is in Motion. 

Now let’s take an example where there is a house of Sheetal and there is one more guy that is Prashant whose house is located at the distance of 500 meters from Sheetal’s house. Where they both are studying in the same school and the distance of school from Prashant’s home is 1200 meters but the distance from Sheetal’s home  is 1300 meters. Now in the morning Sheetal starts walking to her school but first she went to Prashant’s home to take a book and they both went to school. And there’s one more person that is Sheetal’s sister who directly went to school. Here both reached school at the same time but their distance was different. Sheetal covered 1700 meters while going to school and her sister covered 1300 meters.

From the above example we can see that the length of the actual path traveled by an object in motion while going from one point to another is termed as ‘Distance’ and the minimum distance from the starting point and the finishing point is called ‘Displacement’.

Speed and Velocity:-

In 8th Standard, we saw the term i.e

Speed = Distance/Time

So, the total distance traveled per unit time is termed as ‘speed’ and that distance traveled in a particular direction by an object in unit time is termed as ‘Velocity’. 

From the above definition unit time can be of one second , one minute , one hour, etc .  One year can also be used as a large unit of time.  

The displacement that occurs in unit time is called ‘Velocity.’

Velocity = Displacement/Time

Some important points related to Speed and Velocity :-

i)   The S.I. the unit of Speed and Velocity is m/s and that in the CGS system is cm/s.  

ii) Speed and Velocity are directly proportional  to distance and displacement respectively.

iii)  The values of speed and velocity can be the same when the motion is along a straight line otherwise they can be different.

iv) Velocity of an object depends on speed as well as direction and that velocity changes by changing the speed while keeping the direction the same or changing the direction while keeping the speed same or changing the speed as well as the direction.

Speed of light

Galileo was the first scientist to measure speed as the distance/time. according to him the speed of sound in air is 343.2 m/s  while the speed of light is 3 x108m/s. The speed of Earth revolution around the sun is about 29770 m/s.

Uniform and non uniform linear motion

Let’s take an example of a car which covers an equal distance in equal time interval, it is said to be moving with non uniform speed.If that car covers equal distances in equal time intervals then it is said to be moving with uniform speed.

Acceleration: The rate of change of velocity with respect to time is termed as acceleration. Acceleration = Change in velocity/Time                                    

Where, Acceleration = (Final velocity – Initial velocity)/Time

Positive, negative and zero acceleration

An object can have positive or negative acceleration. When the speed of an object increases, the acceleration is positive. During this case, the acceleration is within the direction of velocity. When the speed of an object decreases with time, it’s negative acceleration.

Negative acceleration is additionally called deceleration. Its direction is opposite to the direction of velocity. If the speed of the thing doesn’t change with time, it’s zero acceleration. If an object is in motion along a line with initial velocity ‘u’.

It attains a final velocity ‘v’ in time ‘t’ due to acceleration ‘a’ its displacement is ‘s’. The three equations of motion are often written as;

v = u + at, this is often the relation between velocity and time.

s = ut + at², this is often the relation between displacement and time.

v² = u²+ 2as, this is often the relation between displacement and velocity.

Chapter 2: Matter In Our Surroundings

 Matter is formed from small particles. The matter around us exists in three states— solid, liquid and gas.

The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases. The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids,intermediate in liquids and maximum in gases.

The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over one another while for gases, there’s no order, particles just move about randomly.

The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.

Sublimation is the change of gaseous state directly to solid state without browsing liquid state, and the other way around.

Boiling may be a bulk phenomenon. Particles from the majority (whole)of the liquid become vapour state.

Evaporation is a surface phenomenon. Particles from the surface gain enough energy to beat the forces of attraction present within the liquid and alter into the vapour state.

The rate of evaporation depends upon the area exposed to the atmosphere, the temperature, the humidity and the wind speed.

Evaporation causes cooling. Latent heat of evaporation is the heat required to change 1 kg of a liquid to gas at air pressure at its boiling point. Latent heat of fusion is the amount of warmth energy required to change 1 kg of solid into liquid at its freezing point.

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Class 9 Science Chapter 3: Atoms & Molecules

During a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is often known as the Law of Conservation of Mass.

In a pure compound , elements are always present in definite proportion by mass. This is known as the Law of Definite Proportions.

An atom is the smallest particle of the element which will exist independently and retain all its chemical properties.

class 9 science chapter 3

A molecule is the smallest particle of a component or a compound capable of independent existence under ordinary conditions.It shows all the properties of the substance.

A chemical formula of a compound shows its constituent elements and therefore the number of atoms of every combining element.

Clusters of atoms that act as an ion are called poly-atomic ions.They carry a hard and fast charge on them.

The formula of a molecular compound is determined by the valency of every element.

In ionic compounds, the charge on each ion is employed to determine the formula of the compound.

Scientists use the relative mass scale to match the masses of different atoms of elements. Atoms of carbon-12 isotopes are assigned a relative atomic mass of 12 and the relative masses of all other atoms are obtained by comparison with the mass of a carbon-12 atom.

The Avogadro constant 6.022 × 1023 is defined because the number of atoms is just 12 g of carbon-12.

The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in just 12 g of carbon-12.

Mass of 1 mole of a substance is named its molar mass.

Chapter 4: Structure of Atom

Credit for the discovery of electrons and protons goes to J.J.Thomson and E.Goldstein, respectively.

J.J. Thomson proposed that electrons are embedded in a positive sphere.

Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.

Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around the nucleus. the steadiness of the atom couldn’t be explained by this model.

Neils Bohr’s model of the atom was more successful. He Proposed that electrons are distributed in several shells with discrete energy round the nucleus. If the atomic shells are complete, then the atoms are going to be stable and fewer reactive.

J. Chadwick discovered the presence of neutrons within the nucleus of an atom. So, the three subatomic particles of an atom are:(i) electrons, (ii) protons and (iii) neutrons. Electrons are negatively charged, protons are charged and neutrons have no charges. The mass of an electron is about 12000 times the mass of an atom . The mass of a proton and neutron is taken together unit each.

Shells of an atom are designated as K,L,M,N,….

Valency is the combining capacity of an atom.

The number of a component is the same because the number of protons within the nucleus of its atom.

The nucleon number of an atom is adequate to the amount of nucleons in its nucleus.

Isotopes are atoms of an equivalent element, which have different mass numbers.

Isobars are atoms having an equivalent nucleon number but different atomic numbers.

Elements are defined by the amount of protons they possess.

Class 9 Science Chapter 5: The Fundamental Unit of Life

The fundamental organisational unit of life is that the cell.

Cells are enclosed by a cell wall composed of lipids and proteins.

The cell wall is a lively a part of the cell. It regulates the movement of materials between the ordered interior of the cell and the outer environment.

In plant cells, a cell wall composed mainly of cellulose is located outside the cell membrane.

The presence of the cell membrane enables the cells of plants, fungi and bacteria to exist in hypotonic media without bursting.

The nucleus in eukaryotes is separated from the cytoplasm by a double-layered membrane and it directs the life processes of the cell.

The ER functions both as a passageway for intracellular transport and as a producing surface.

The Golgi apparatus consists of stacks of membrane-bound vesicles that function within the storage, modification and packaging of substances manufactured within the cell.

Most plant cells have large membranous organelles called plastids, which are of two types – chromoplasts and leucoplasts.

Chloroplasts that contain chlorophyll are called chloroplasts and they perform photosynthesis.

The primary function of leucoplasts is storage.

Most mature plant cells have an outsized central vacuole that helps to maintain the turgidity of the cell and stores important substances including wastes.

Prokaryotic cells haven’t any membrane-bound organelles, their chromosomes are composed of only macromolecules , and that they have only very small ribosomes as organelles.

Chapter 6: Tissues

Tissue may be a group of cells similar in structure and performance .

Plant tissues are of two main types – meristematic and permanent.

Meristematic tissue is the dividing tissue present within the growing regions of the plant.

Permanent tissues are derived from meristematic tissue once they lose the power to divide. they’re classified as simple and complex tissues.

Parenchyma, collenchyma and sclerenchyma are three types of simple tissues. Xylem and phloem are types of complex tissues.

Animal tissues can be epithelial, connective, muscular and nervous tissue.

Depending on shape and performance , epithelium is classified as squamous, cuboidal, columnar, ciliated and glandular.

The differing types of connective tissues in our body include areolar tissue, fat , bone, tendon, ligament, cartilage and blood.

Striated, striated and cardiac are three types of muscle tissues.

Nervous tissue is formed of neurons that receive and conduct impulses.

Class 9 Science Chapter 7: Diversity In Living Organism

Classification helps us in exploring the range of life forms.

The major characteristics considered for classifying all organisms into five major kingdoms are:-

(a) whether or not they are made from prokaryotic or eukaryotic cells

(b) whether the cells live singly or organised into multi-cellular and thus complex organisms

(c) whether the cells have a cell-wall and whether or not they prepare their own food.

All living organisms are divided on the above bases into five kingdoms, namely Monera, Protista, Fungi, Plantae and Animalia.

micro organisms

The classification of life forms is said to be their evolution.

Plantae and Animalia are further divided into subdivisions on the basis of accelerating complexity of body organisation.

Plants are divided into five groups: Thallophytes, Bryophytes,Pteridophytes, Gymnosperms and Angiosperms.

Animals are divided into ten groups: Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata, Protochordates and Vertebrata.

The binomial nomenclature makes for a uniform way of identification of the vast diversity of life around us.

The binomial nomenclature is formed from two words – a generic-name and a selected name.

Chapter 8: Force & Laws of Motion

First law of motion: An object continues to be during a state of rest or of uniform motion along a line unless acted upon by an unbalanced force.

The natural tendency of objects to resist a change in their state of rest or of uniform motion is called inertia.

The mass of an object may be a measure of its inertia. Its SI unit is kilogram (kg). Force of friction always opposes motion of objects.

Second law of motion: the speed of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.

The SI unit of force is kg ms^-2. This is often also referred to as newton and represented by the symbol N.A force of one newton produces an acceleration of 1 ms^-2 on an object of mass 1 kg.

The momentum of an object is the product of its mass and velocity and has an equivalent direction as that of the speed . Its SI unit is kg ms^-1.

Third law of motion: To every action, there is an equal and opposite reaction and that they act on two different bodies.

In an isolated system, the entire momentum remains conserved.


All conservation laws like conservation of momentum, energy, momentum ,charge etc. are considered to be fundamental laws in physics. These are based on observations and experiments. it’s important to recollect that a conservation law cannot be proved. It are often verified, or disproved, by experiments. An experiment whose result is in conformity with the law verifies or substantiates the law; it doesn’t prove the law. On The other hand, one experiment whose result goes against the law is enough to disprove it.The law of conservation of momentum has been deduced from a large number of observations and experiments. This law was formulated nearly three centuries ago. It’s Interesting to notice that not one situation has been realised thus far , which contradicts this law. Several experiences of every-day life are often explained on the idea of the law of conservation of momentum.

Class 9 Science Chapter 9: Gravitation

The law of gravitation states that the force of attraction between any two objects is proportional to the merchandise of their masses and inversely proportional to the square of the space between them. The law applies to things anywhere within the universe.Such a law is claimed to be universal.

Gravitation may be a weak interaction unless large masses are involved.

Force of gravitation thanks to the world is named gravity.

The force of gravity decreases with altitude. It also varies on the surface of the world , decreasing from poles to the equator.

The weight of a body is the force with which the earth attracts it.

The weight is adequate to the merchandise of mass and acceleration due to gravity.

The weight may vary from place to put but the mass stays constant.

All objects experience a force of buoyancy when they are immersed during a fluid.

Objects having density less than that of the liquid in which they are immersed, float on the surface of the liquid. If the density of the thing is quite the density of the liquid in which it is immersed then it sinks within the liquid.

Chapter 10: Work & Energy

Work done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force. 

The unit of work is joule: 1 joule = 1 newton × 1 metre.

Work done on an object by a force would be zero if the displacement of the thing is zero.

An object having capability to try to to work is claimed to possess energy. Energy has an equivalent unit as that of labor.

An object in motion possesses what’s referred to as the kinetic energy of the thing . An object of mass m moving with velocity v features a K.E. of 1/2 mv^2.

The energy possessed by a body thanks to its change in position or shape is called the potential energy. The gravitational potential energy of an object of mass, m raised through a height,h from the earth’s surface is given by m g h.

According to the law of conservation of energy, energy can only be transformed from one form to another; it can neither be created nor destroyed. The total energy before and after the transformation always remains constant.

Energy exists in nature in several forms like K.E. ,potential energy, heat , energy etc. The sum of the kinetic and potential energies of an object is called its mechanical energy.

Power is defined because of the rate of doing work. The SI unit of power is watt. 1 W = 1 J/s.•The energy utilized in one hour at the speed of 1kW is named 1 kWh.

Unit of work

Work = Force × Displacement 

In SI system, the unit of force is newton (N) and the unit of displacement is metre (m). Thus, the unit of force is newton-metre. This is called joule. 

1 Joule : If a force of 1 newton displaces an object through 1 metre in the direction of the force, the amount of work done on the object is 1 joule. 

 1 joule = 1 newton x 1 metre

 1 J = 1 N x 1 m 

In CGS system, the unit of force is dyne and that of displacement is centimeter (cm). Thus, the unit of work done is dyne-centimetre. This is called an erg. 1 erg : If a force of 1 dyne displaces an object through 1 centimetre in the direction of the force, the amount of work done is 1 erg. 

1 erg = 1 dyne x 1 cm 

Relationship between joule and erg 

We know that, 1 newton = 10^5 dyne and 1 m = 10^2 cm

 Work = force x displacement 

1 joule = 1 newton x 1 m

 1 joule = 10^5 dyne x 10^2cm =10^7 dyne cm

 1 joule = 10^7 erg

Class 9 Science Chapter 11: Sound

Sound is produced thanks to the vibration of various objects.

Sound travels as a longitudinal wave through a material medium.

Sound travels as successive compressions and rarefactions in the medium.

In sound propagation, it’s the energy of the sound that travels and not the particles of the medium.

Sound cannot travel in vacuum.

The change in density from one maximum value to the minimum value and again to the utmost value makes one complete oscillation.

The distance between two consecutive compressions or two consecutive rarefactions is named the wavelength, λ.

The time taken by the wave for one complete oscillation of the density or pressure of the medium is named the period of time , T.

The number of complete oscillations per unit time is called the frequency (ν), 1=νT.

The speed v, frequency ν, and wavelength λ, of sound are related by the equation, v = λν.

The speed of sound depends totally on the character and the temperature of the transmitting medium.

The law of reflection of sound states that the directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface and therefore the three dwell in the same plane.

For hearing a distinct sound, the time interval between the original sound and therefore the reflected one must be a minimum of 0.1 s.

The persistence of sound in an auditorium is the result of repeated reflections of sound and is named reverberation.

Sound properties such as pitch, loudness and quality are determined by the corresponding wave properties.

Loudness may be a physiological response of the ear to the intensity of sound.

The amount of sound energy passing each second through the unit area is named the intensity of sound.

The audible range of hearing for average citizens is the frequency range of 20 Hz – 20 kHz.

Sound waves with frequencies below the audible range are termed “infrasonic” and those above the audible range are termed “ultrasonic”.

Ultrasound has many medical and industrial applications.

The SONAR technique is employed to work out the depth of the sea and to locate underwater hills, valleys, submarines, icebergs, sunken ships etc.

Uses of ultrasonic sound

1. For communication between ships stumped .

2. to hitch plastic surfaces together.

3. To sterilize liquids like milk by killing the bacteria in it in order that the milk keeps for a

longer duration.

4. Echocardiography which studies heartbeats, is predicated on ultrasonic waves

(Sonography technology).

5. to get images of internal organs during a physical body .

6. In industry, to wash intricate parts of machines where hands cannot reach.

7. To locate the cracks and faults in metals blocks.

Chapter 12: Natural Resources

Life on Earth depends on resources like soil, water and air,and energy from the Sun.

Uneven heating of air over land and water-bodies causes winds.

Evaporation of water from water-bodies and subsequent condensation give us rain.

Rainfall patterns depend upon the wind patterns in an area.

Various nutrients are used again and again during a cyclic fashion.This results in a particular balance between the varied components of the biosphere.

Pollution of air, water and soil affect the quality of life and harm the biodiversity.

We got to conserve our natural resources and use them in a sustainable manner.

Class 9 Science Chapter 13: Improvement In Human Resources

There are thirteen nutrients essential for crops. Of these, six are required in large quantities and are known as macro-nutrients whereas seven nutrients are required in small quantities and are referred to as micronutrients.

Manure and fertilizers are the most sources of nutrient supply to crops.

Organic farming is a farming system with minimal or no use of chemicals as fertilizers, herbicides, pesticides etc.and with a maximum input of organic manures, recycled farm wastes, and bio-agents, with healthy cropping systems.

Mixed farming is a system of farming on a particular farm which includes crop production, raising of livestock etc.

Mixed cropping is growing two or more crops simultaneously on an equivalent piece of land.

Growing two or more crops in definite row patterns is known as intercropping.

The growing of various crops on a bit of land in pre-planned succession is named crop rotation.

Varietal improvement is required for higher yield, good quality,biotic and abiotic resistance, shortening the maturity duration,wider adaptability and desirable agronomic characteristics.

Farm animals require proper care and management such as shelter, feeding, breeding and disease control. This is called animal husbandry.

Poultry farming is done to raise domestic fowls. Poultry Production includes egg production and broiler production for poultry meat.

To enhance poultry production, cross breeding is completed between Indian and exotic breeds for variety improvement.

Fish could also be obtained from marine resources also as inland resources.

To increase production of fish, they will be cultured in marine and inland ecosystems.

Marine fish capture is completed by fishing nets guided by echo-sounders and satellites.

Composite fish culture system is commonly used for fish farming.

Bee-keeping is completed to urge honey and wax.

This was all about class 9 science. I hope you understood each concept more clearly about class 9 science.

Also, I’m looking for your questions and queries related to class 9 science.

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