class 9 science notes

 

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Introduction to Structure of an Atom

Atoms

Atoms are the building blocks of matter. It is the smallest unit of matter that is composed of three sub-atomic particles: the proton, the neutron and the electron.

Cathode ray experiment

• J. J. Thomson discovered the existence of electrons.
• He did this using a cathode ray tube, which is a vacuum-sealed tube with a cathode and anode on one end that created a beam of electrons travelling towards the other end of the tube.
• The air inside the chamber is subjected to high voltage and electricity flows through the air from the negative electrode to the positive electrode.
• The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.
• The experiment showed that the atom was not a simple, indivisible particle and contained at least one subatomic particle – the electron.

Apparatus of the experiment

Electrons

• Electrons are the negatively charged sub-atomic particles of an atom.
• The mass of an electron is considered to be negligible, and its charge is -1.
• The symbol for an electron is e^–
• Electrons are extremely small.
• They are found outside the nucleus.

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Thomson’s model of an atom

• According to Thomson,(i) An atom consists of a positively charged sphere and the electrons are embedded in it. (ii) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral
• The first model of an atom to be put forward and taken into consideration.
• He proposed a model of the atom be similar to that of a Christmas pudding/watermelon.
• The red edible part of the watermelon is compared with the positive charge in the atom.
• The black seeds in the watermelon are compared with the electrons which are embedded on it.

Radioactivity

Radioactivity

• Radioactivity is the term for the process by which an unstable nucleus of an atom loses energy by giving out particles.
• It does so by giving out particles such as alpha and beta particles.
• This process is spontaneous.
• An atom is unstable if the nucleus has an imbalance, meaning a difference in the protons and neutrons.

Rutherford Model

Rutherford’s experiment and observations

In this experiment, fast-moving alpha (α)-particles were made to fall on a thin gold foil. His observations were:

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• A major fraction of the α-particles bombarded towards the gold sheet passed through it without any deflection, and hence most of the space in an atom is empty.
• Some of the α-particles were deflected by the gold sheet by very small angles, and hence the positive charge in an atom is not uniformly distributed.
• The positive charge in an atom is concentrated in a very small volume.
• Very few of the α-particles were deflected back, that is only a few α-particles had nearly 180o angle of deflection. So the volume occupied by the positively charged particles in an atom is very small as compared to the total volume of an atom.

Rutherford’s model of an atom

Rutherford concluded the model of the atom from the α-particle scattering experiment as:

(i) There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.

(ii) The electrons revolve around the nucleus in well-defined orbits.

(iii) The size of the nucleus is very small as compared to the size of the atom.

Rutherford’s Model

Drawbacks of Rutherford’s model

• He explained that the electrons in an atom revolve around the nucleus in well-defined orbits. Particles in a circular orbit would experience acceleration.
• Thus, the revolving electron would lose energy and finally fall into the nucleus.
• But this cannot take place as the atom would be unstable and matter would not exist in the form we know.

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Be More Curious!!!

• The Millikan’s Oil Drop Experiment was an experiment performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the charge of an electron.
• In the experiment, Millikan allowed charged tiny oil droplets to pass through a hole into an electric field.
• By varying the strength of electric field, the charge over an oil droplet was calculated, which always came as an integral value of ‘e.’
• The conclusion of this is that the charge is said to be quantized, i.e. the charge on any particle will always be an integral multiple of e which is 1.6*10^-19

Neil Bohr Model

Properties of electrons, protons and neutrons

Bohr’s Model of an atom

Bohr came up with these postulates to overcome the objections raised against Rutherford’s model:

• Electrons revolve around the nucleus in stable orbits without emission of radiant energy. Each orbit has a definite energy and is called an energy shell or energy level.
• An orbit or energy level is designated as K, L, M, N shells. When the electron is in the lowest energy level, it is said to be in the ground state.
• An electron emits or absorbs energy when it jumps from one orbit or energy level to another.
• When it jumps from a higher energy level to lower energy level, it emits energy while it absorbs energy when it jumps from lower energy level to higher energy level.

Bohr’s Model

Orbits

Orbits are energy shells surrounding the nucleus in which electrons revolve.

Electron distribution in different orbits

The distribution was suggested by Bohr and Bury;

• The maximum number of electrons present in a shell is given by the formula 2n², where ‘n’ is the orbit number or energy level index, 1,2,3,….
• The maximum number of electrons in different shells are as follows: the first orbit will have 2*1²=2, the second orbit will have 2*2Msup>2=8, the third orbit will have 2*3²=18, fourth orbit 2*4²=32 and so on.
• The shells are always filled in a step-wise manner from the lower to higher energy levels. Electrons are not filled in the next shell unless previous shells are filled.

Valency

• The electrons present in the outermost shell of an atom are known as the valence electrons.
• The combining capacity of the atoms or their tendency to react and form molecules with atoms of the same or different elements is known as valency of the atom.
• Atoms of elements, having a completely filled outermost shell show little chemical activity.
• Their combining capacity or valency is zero.
• For example, we know that the number of electrons in the outermost shell of hydrogen is 1, and in magnesium, it is 2.
• Therefore, the valency of hydrogen is 1 as it can easily lose 1 electron and become stable.
• On the other hand, that of magnesium is 2 as it can lose 2 electrons easily and also attain stability.

Atomic Number

The number of protons found in the nucleus of an atom is termed as the atomic number. It is denoted by the letter ‘Z’.

Mass number and representation of an atom

Protons and neutrons are present in the nucleus, so the mass number is the total of these protons and neutrons.

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Isotopes and Isobars

Isotopes are defined as the atoms of the same element, having the same atomic number ( number of protons ) but different mass numbers ( number of protons+neutrons ).
For example: In the case of Hydrogen we have:

Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars.
For example, Calcium and Argon: both have the same mass number – 40
₂₀Ca⁴⁰ and ₁₈Ar⁴⁰

Calculation of mass number for isotopic elements

When an element has an isotope, the mass number can be calculated by the different proportions it exists in.

For example take 98% Carbon-12u and 2% Carbon-13u

This does not mean that any Carbon atoms exists with the mass number of 12.02u. If you take a certain amount of Carbon, it will contain both isotopes of Carbon, and the average mass is 12.02 u.

Chapter 4: Structure of an Atom

What are the features of ‘Thomas atomic model’?

J.J. Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom.

Who was ‘Ernest Rutherford’?

Ernest Rutherford was a New Zealand physicist who came to be known as the father of nuclear physics.

What did ‘Neils Bohr’ discover?

Niels Bohr proposed a theory for the hydrogen atom, based on quantum theory that some physical quantities only take discrete values.

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CBSE Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

Facts that Matter

The smallest functional unit of life is a cell, discovered by Robert Hooke in 1665. A cell can independently perform all necessary activities to sustain life. Hence cell is the basic unit of life.
There are two types of cells plant cell and animal cell. The different cell organelles and their functions are as follows:

1. Plasma/Cell membrane: This is the outermost covering of the cell that separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell so the cell membrane is called a selectively permeable membrane.

Some substances like CO₂ or O₂  gases can move across the cell membrane by a process called diffusion. The movement of water molecules (liquid) through such a selectively permeable membrane is called osmosis. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
If the medium surrounding the cell has a higher water concentration than the cell, the cell will gain water by osmosis. Such a solution is known as a hypotonic solution.

If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is known as an isotonic solution. If the medium has a lower water concentration then the cell will lose water by osmosis. Such a solution is known as a hypertonic solution.

The plasma membrane is flexible and is made up of organic molecules called lipids and proteins. The flexibility of cell membrane also enables the cell to engulf in food and other material from its external environment. Such process is known as endocytosis. It is observed in Amoeba.

2. Cell wall (Protective wall): Plants cells, in addition to the plasma membrane have another rigid outer covering called cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose. It is a complex substance and provides structural strength to plant cells. When a living plant loses water through osmosis there is shrinkage or contraction of contents of the cell away from cell wall. This phenomenon is known as plasmolysis.

3. Nucleus (Brain of a cell): The nucleus has a double-layered covering called nuclear membrane. The nuclear membrane has pores which allow the transfer of material from inside the nucleus to its outside, i.e., to the cytoplasm.

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The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.
Chromosomes — contain information for inheritance of features from parents to next generation in form of DNA [Deoxyribo Nucleic Acid] molecules. Chromosomes are composed of DNA and protein. Functional segments of DNA are called genes. The nucleus plays a central role in cellular reproduction.

Prokaryotic Cells: In some organisms like bacteria, the nuclear material is not enclosed by nuclear membrane and membrane bound cell organelle are absent. Such nucleus is called nucleoid and such cells are known as prokaryotic cell. Such cells have single chromosome.
Eukaryotic Cells: Cells having well defined nucleus and having membrane bound cell organelle is termed as eukaryotic cell. Such cells have more than one chromosomes.

4. Cytoplasm: The cytoplasm is the fluid content inside the plasma membrane. It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.

5. Cell Organelles: Every cell has a membrane around it to keep its content separate from the external environment. The different components of cell perform different function and these components are called cell organelles.
(i) Endoplasmic Reticulum (ER) (Channels, Network for transport):

The ER is a large network of membrane-bound tubes and sheets. It looks like long tubules or round or oblong bags.
There are two types of ER-Rough endoplasmic reticulum [RER] and smooth endoplasmic reticulum [SER]. RER has particles called ribosomes attached to its surface. The ribosomes Endoplasmic Reticulum are the sites of protein manufacture.

The SER helps in the manufacture of fat molecules, or lipids, important for cell function. Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis. Some other proteins and lipids function as enzymes and hormones.

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The one function of ER is to serve as channels for the transport of materials between various regions of the cytoplasm or between the cytoplasm and the nucleus. The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.

(ii) Golgi Apparatus (Packaging): The golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately, parallel to each other in stacks called cisterns.
The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. It’s function include the storage, modification and packages of products in vesicles. In some cases complex sugar may be made from simple sugar in the Golgi apparatus. It is also involved in the formation of lysosomes.

(iii) Lysosomes [Suichge bags] (Cleanliness of cell): Lysosomes are a kind of waste dispatch and disposal system of the cell. Lysosome help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. Foreign materials entering the cells such as bacteria or food, as well as old organelles, end up in the lysosome, which break them up into small pieces. They are able to do this because they contain powerful digestive enzymes capable of breaking down all organic material. Under abnormal condition, when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore they are also known as “suicide bags”

(iv) Mitochondria (Powerhouse, Energy provider): Mitochondria are known as powerhouses of the cell. The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP [Adenosine Triphosphate] molecules. ATP is known as energy currency of the cell. Mitochondria have two membrane coverings instead of just one. The outer membrane is very porous while the inner membrane is deeply folded. They are able to make some of their own protein.

(v) Plastids: Plastids are present only in plant cells. There are two types of plastids chromoplasts and leucoplasts. Chromoplasts are the coloured plastids present in leaves, flowers and fruits. Plastids containing the pigment chlorophyll are known as chloroplasts. They are important for photosynthesis in plants. Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll. Leucoplasts are found primarily in organelles in which materials such as starch, oils and protein granules are stored.

The internal organisation of the plastids consists of numerous membrane layers embedded in a material called stroma. Plastids are similar to mitochondria in external structure. Plastids have their own DNA and ribosomes.

(vi) Vacuoles (Storage): Vacuoles are storage sacs for solid or liquid contents. Vacuoles are small-sized in animal cells while plant cells have very large vacuoles [50% to 90% cell volume].

In plant cells, vacuoles are full of cell sap and provide turgidity and rigidity to the cell. In Amoeba, the food’vacuole contain the food items that is consumed it and contractile vacuoles expels excess water and some wastes from the cell.

 

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MOB-9450149685

DR OMAR CLASSES BARRA, MOBILE 9450149685

Matter in Our Surroundings Class 9 Notes Understanding the Lesson

1. Matter is everything around you. Everything in this universe is made up of material which in scientific term is called matter.

2. Matter can be defined as anything that occupies space possesses mass, offers resistance and can be felt by one or more of our senses.

3. Examples: Water, air, plant, animal, stones, clouds, etc.
Matter is classified on the basis of their physical and chemical nature.

·         Physical classification: On the basis of physical properties, matter has been classified as solid, liquid and gas.

·         Chemical classification: On the basis of chemical composition, matter has been classified as element, compound and mixture.

4. Properties of Matter

·         Matter is made up of small particles.

·         Particles of matter have space between them.

·         Particles of matter are continuously moving.

·         Particles of matter attract each other because of force of attraction.

5. States of Matter
This classification is done on the basis of arrangement among particles, energy of particles and the distance between the particles.
(i) Solids:

·         They have fixed shape and definite volume.

·         They have small interparticle distances.

·         They are incompressible.

·         They are rigid.

·         They have high density and do not diffuse.

·         They have strong intermolecular forces of attraction.

·         Their constituent particles are very closely packed.

·         Their kinetic energy is very less.
Examples: Sugar, salt, etc.

 (ii) Liquids:

·         They do not have fixed shape but have fixed volume.

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·         Their interparticle distances are larger than solids.

·         They are almost incompressible.

·         They have low density than solids.

·         Their interparticle forces of attraction are weaker than solids.

·         Their constituent particles are less closely packed.

·         They assume the shape of the portion of the container they occupy.

·         They can flow and thus can be called fluids.

·         The kinetic energy of particles is more than that of solids.

·         Examples: Milk, water, etc.

(iii) Gases:

·         They have neither fixed shape nor fixed volume.

·         Their interparticle distances are largest among the three states of matter.

·         They have high compressibility.

·         They have least density and diffuse.

·         Their interparticle forces of attraction are weakest.

·         Their constituent particles are free to move about.

·         They can expand to occupy larger volume.

·         They are also called vapour.

·         The particles of gases have maximum kinetic energy.

·         Examples: H₂, N₂, CO₂ etc.

6. Interchange of States of Matter

·         Matter can be changed from one state to another state.

·         Most of the metals, which are solid change into liquid on heating and then into vapour on further heating.

·         The change of state of matter depends on:
(i) Temperature
(ii) Pressure

7. Effect of Change of Temperature

8. The temperature effect on heating a solid varies depending on the nature of the solid and the conditions required for bringing the change.

9. Generally on heating, temperature of substances increases. But during state transformation, temperature remains same.

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10. On heating: The kinetic energy of particles increases which overcomes the force of attraction between the particles thereby solid melts and is converted to a liquid.

11. Melting point: It is the temperature at which a solid changes to a liquid at atomospheric pressure.

12. Different substances have different melting points.

13. Higher the melting point means large forces of attraction between the particles.

14. Melting point of ice is 273.16 K.

15. The process of melting is also known as fusion.

16. Melting point is characteristic propertyof a substance.

17. Latent heat: The hidden heat which breaks the force of attraction between the molecule is called latent heat.

18. It is the heat supplied to a substance during the change of its state.

19. It is the heat energy hidden in the bulk of matter.

20. Latent heat of fusion: Amount of heat energy required to convert 1 kg of a solid into a liquid at atmospheric pressure at its melting point is known as latent heat of fusion of a substance.

21. A solid having stronger interparticle forces has greater latent heat of fusion.

22. Latent heat of fusion of water is 333.7 kJ/kg.

23. Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point.

24. A liquid having weaker interparticle forces has lower boiling point and is more volatile.

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25. Latent heat of vapourisation: The amount of heat energy required to convert 1 kg of a liquid into a gas at atmospheric pressure at its boiling point is known as latent heat of vapourisation of the substance.

26. Latent heat of vapourisation of water is 2259 kJ/kg. Thus 1 kg of water in the form of steam at 373 K has 2259 kJ more energy than 1 kg of water at 373 K.

27. Condensation: The change of state from gas to liquid is called condensation.

28. The condensation process is reverse of vapourisation.

29. Freezing: The change of state from liquid to solid is called freezing.

30. Freezing is the reverse of melting or fusion.

31. Sublimation: Sublimation involves direct conversion of a solid into the gaseous state on heating and vice-versa.

32. Dry ice sublimes at -78 °C (195 K).

33. Camphor, ammonium chloride, iodine and naphthalene are some substances which undergo sublimation.

34. Effect of Change of Pressure

In the gaseous state, the interparticle spaces are very large and attractive forces between the particles are negligible. Because of large interparticle space, gases are highly compressible. When pressure is applied on a gas, enclosed in a cylinder, its molecules move closer and the gas undergoes appreciable compression. As the molecules move closer, the attractive forces between the molecules increase. At a sufficiently high pressure, the gas changes into liquid.

(i) Solid CO₂ is stored under high pressure. At a pressure of 1 atmosphere, solid CO₂ changes directly into gas without passing through the liquid state. Solid CO₂ is known as dry ice. Thus, we can conclude that we can liquefy gas by applying pressure and reducing temperature.

 

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(ii) Change in volume from gaseous state to liquid state is very large whereas change in volume from liquid state to solid state is very small (negligible). This is due to the reason that in liquid the interparticle spaces are very small in a liquid.

(iii) Atmospheric pressure: The pressure exerted by the atmosphere or air is called atmospheric pressure. It decreases with increase in height.

(iv) Atmosphere (atm) is a unit of pressure.

(v) The SI unit of pressure is pascal (pa).
1 atm = 1.01 x 10⁵pa
1 bar = 1 x 10⁵ pa 1
bar = 1.01 atm.

(vi) Evaporation: The phenomenon of change of a liquid into vapour at any temperature below its boiling point is called evaporation.

(vii) Particles of matter possess kinetic energy. At a particular temperature, in a sample of liquid all the particles do not have same kinetic energy. There is a small fraction of molecule which has enough kinetic energy to overcome the attractive forces of other particles. If such a particle happens to come near the surface, it escapes into vapour state and evaporation takes place.

35. Factors Affecting the Rate of evaporation

(i) Surface area: Evaporation is a surface phenomenon, i.e., only the particles on the surface of the liquid gets converted into vapour. Thus, greater is the surface area, more is the rate of evaporation. For example, clothes dry faster when they are well spread out.

(ii) Increase in temperature: The rate of evaporation increases with increase in temperature. At higher temperature greater number of particles have enough kinetic energy to escape into the vapour state. For example, clothes dry faster in summer than in winter.

(iii) Decrease in humidity: The amount of water vapour present in air is referred to as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature. If the humidity is more, the rate of evaporation decreases. For example, clothes do not dry easily during rainy season because the rate of evaporation is less due to high moisture content in the air.

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(iv) Increase in the speed of the wind: With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding. For example, wet clothes dry faster on a windy day.

(v) Nature of liquid: Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at a faster rate because less energy is required to overcome the attractive forces. For example, acetone evaporates faster than water.

(vi) Evaporation causes cooling: Only the liquid particles having high kinetic energy leave the surface of the liquid and get converted into vapour. As a result, the average kinetic energy of the remaining particles of the liquid decreases and hence the temperature falls. Thus, evaporation causes cooling.

Class 9 Science Chapter 1 Important Definitions

Melting Point: It is the temperature at which a solid changes into liquid at atmospheric pressure.

Freezing point: The temperature at which a liquid freezes to become a solid at atmospheric pressure is called the freezing point.

Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is called its boiling point.

Latent heat of vapourisation: The amount of heat energy that is required to change 1 kg of liquid into vapour at atmospheric pressure at its boiling point is called latent heat of vapourisation.

Condensation: The process of changing a gas (or vapour) to a liquid by cooling is called condensation. Sublimation: Sublimation involves direct conversion of a solid into the gaseous state on heating and vice-versa.

Latent heat: The hidden heat which breaks the force of attraction between the molecules is known as latent heat.

Latent heat of fusion: The heat of energy required to convert 1 kg of a solid into liquid at atmospheric pressure, as its melting point, is known as latent heat of fusion.

Boiling: Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.

Evaporation: Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the force of attraction present in the liquid and change into vapour state.

 

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States of Matter

• Matter can be classified as solid, liquid and gas on the basis of interparticle forces and the arrangement of particles.
• These three forms of matter are interconvertible by increasing or decreasing pressure and temperature.  For example, ice can be converted from solid to a liquid by increasing the temperature.

• Property	Solid	Liquid	Gas
  Shape and volume	Fixed shape and volume	No fixed shape but has volume	Neither definite shape nor volume
  Energy	Lowest	Medium	Highest
  Compressibility	Difficult	Nearly difficult	Easy
  Arrangement of molecules	Regular and closely arranged	Random and little sparsely arranged	Random and more sparsely arranged
  Fluidity	Cannot flow	Flows from higher to lower level	Flows in all directions
  Movement	Negligible	Depends on interparticle attraction	Free, constant and random
  Interparticle space	Very less	More	Large
  Interparticle attraction	Maximum	Medium	Minimum
  Density	Maximum	Medium	Minimum
  Rate of diffusion	Negligible	It depends on interparticle attraction.	Maximum

  
  

Atomic view of the three states of matter

Solid

Liquid

Gas

Evaporation

The phenomenon by which molecules in liquid state undergo a spontaneous transition to the gaseous phase at any temperature below its boiling point is called evaporation.

• For example, the gradual drying of damp clothes is caused by the evaporation of water to water vapour.

• Factors affecting evaporation

  • Temperature: The rate of evaporation increases with an increase in temperature.
  • Surface area: The rate of evaporation increases with an increase in surface area.
  • Humidity: The rate of evaporation decreases with an increase in humidity.
  • Wind speed: The rate of evaporation increases with an increase in wind speed.

  
  

  Cooling due to evaporation

  During evaporation, the particles of a liquid absorb energy from the surroundings to overcome the inter-particle forces of attraction and undergo the phase change. The absorption of heat from the surrounding makes the surrounding cool.
  For example, sweating cools down our body.

  Physical Nature of Matter

• A physical property is that aspect of the matter that can be observed or measured without changing its nature or composition.
• It is independent of the amount of matter present.
• Physical properties include appearance, colour, odour, density, texture, melting point, boiling point, solubility, etc.

• Characteristics of Particles of Matter

  Matter

  Matter is anything that has mass and occupies space.

• Everything that we can touch, see, hear, taste and also smell is matter.
• It is made up of really tiny particles which cannot be seen through the eye.

• The particles of which the matter is comprised influence its state and properties (physical and chemical).

  1. Particles of matter have spaces between them

  • This characteristic is one of the concepts behind the solubility of a substance in other substances. For example, on dissolving sugar in water, there is no rise in water level because the particles of sugar get into the interparticle spaces between the water particles.

  2. Particles of matter are always in motion

  • Particles of the matter show continuous random movements due to the kinetic energy they possess.
  • A rise in temperature increases the kinetic energy of the particles, making them move more vigorously.

  3. Particles of matter attract each other
  In every substance, there is an interparticle force of attraction acting between the particles. To break a substance we need to overcome this force. The strength of the force differs from one substance to another.

  
  

  Diffusion

  When the particles of matter intermix on their own with each other, the phenomenon is called diffusion. For example, spreading of ink in water.

  • During diffusion, the particles occupy the interparticle spaces.
  • The rate of diffusion increases with increase in the temperature, due to increase in kinetic energy of the particles.

  
  

  Can Matter Change Its State?

  Effect of change of temperature on state of matter

  On increasing temperature, the kinetic energy of the particles of the matter increases and they begin to vibrate with a higher energy. Therefore, the interparticle force of attraction between the particles reduces and particles get detached from their position and begin to move freely.

  • As a result, the state of matter begins to change.
  • Solids undergo a phase change to form liquids.
  • Similarly, liquids also undergo a phase change to form gases.

  
  

  Melting point

  The melting point of a solid is defined as the temperature at which solid melts to become liquid at the atmospheric pressure.

  • At melting point, these two phases, i.e., solid and liquid are in equilibrium, i.e., at this point both solid state and liquid state exist simultaneously.

  Boiling point

  The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.

  Latent heat of fusion

  It is the amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.

  Latent heat of vaporisation

  It is the amount of heat energy that is required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point.

  Sublimation

  The transition of a substance directly from its solid phase to gaseous phase without changing into the liquid phase (or vice versa) is called sublimation.

  

  Sublimation – Solid to Gas Phase Transformation

  Effect of change in pressure on state of matter

  By applying pressure, the interparticle spaces between particles of matter decreases. Thus, by applying pressure and reducing temperature we can convert a solid to liquid and a liquid to gas.

  Flowchart for inter-conversion of the three states of matter

  

  Frequently asked Questions on CBSE Class 9 Biology Notes Chapter 1: Matter in Our Surroundings

  What is ‘Latent heat of fusion’?

  The latent heat of fusion is the enthalpy change of any amount of substance when it melts.

  What does ‘Sublimation critical point’ mean?

  Sublimation critical point refers to the maximum or minimum temperature and pressure beyond which the state of the matter cannot be changed.

  What does ‘Interconversion of matter’ mean?

  Interconversion of matter refers to the change of one state to another. It is a process by which matter changes from one state to another and back to its original state, without any change in its chemical composition.

• DR OMAR CLASSES BARRA KANPUR

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Introduction to Force

A force is an effort that changes the state of an object at rest or at motion. It can change an object’s direction and velocity. Force can also change the shape of an object.

Effects of Force

Some effects of force include the following:

• Force moves stationary objects
• Force stops objects from moving
• Force changes the shape of a body
• Force changes the direction of motion

Push is defined as an action of force which causes an object to move from its place. The following are the examples of push:

• Opening and closing of the door.
• Pushing the table.
• Pushing a car.
• Pushing of the thumb pins.
• Walking

Pull is defined as an action to make move by either tugging or dragging. The following are the examples of pull:

• Plucking the string of a guitar.
• Pulling ropes while playing tug of war.
• Opening the drawer.
• Pulling the window curtain.
• Opening and closing of the doors.

Balanced and Unbalanced Forces

When balanced forces are applied to an object, there will be no net effective force acting on the object. Balanced forces do not cause a change in motion.

Unbalanced forces acting on an object change its speed and/or direction of motion. It moves in the direction of the force with the highest magnitude.

 

Net force

When multiple forces act on a body, they can be resolved into one component known as the net force acting on the object. The net force decides the direction of motion.

 

 

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Frictional force

The force that opposes relative motion is called friction. It arises between the surfaces in contact.

Example: When we try to push a table and it does not move is because it is balanced by the frictional force.

First Law of Motion

A body continues to be in the state of rest or uniform motion in a straight line unless acted upon by an external unbalanced force. The First Law is also called the Law of Inertia.

Inertia

Basically, all objects have a tendency to resist the change in the state of motion or rest. This tendency is called inertia. All bodies do not have the same inertia. Inertia depends on the mass of a body. Mass of an object is the measure of its inertia.

More the mass → more inertia and vice versa.

Inertia of Rest

An object stays at rest, and it remains at rest until an external force affects it. Example: When a car accelerates, passengers may feel as though their bodies are moving backward. In reality, inertia is making their bodies stay in place as the car moves forward.

Inertia of Motion

An object will continue to be in motion until a force acts on it. Example: A hockey puck will continue to slide across the ice until acted upon by an outside force.

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Second Law of Motion

In order to understand second law, we need to first understand momentum.

Momentum

Impacts produced by objects depend on their mass and velocity. The momentum of an object is defined as the product of its mass and velocity. p = mv. Vector quantity, has direction and magnitude. Some examples of momentum include: A baseball flying through the air and a bullet fired from a gun.

Second Law of Motion

The rate of change of momentum of an object is directly proportional to the applied unbalanced force in the direction of the force.

\(\begin{array}{l}\frac{\Delta p}{t}\alpha \frac{m(v-u)}{t}\end{array} \)

Here, a [ = (v – u)/t ] is the acceleration, which is the rate of change in velocity.

\(\begin{array}{l}\frac{\Delta p}{t}\alpha ma\end{array} \)

\(\begin{array}{l}F \alpha ma\end{array} \)

F = kma

For 1 unit of force on 1 kg mass with the acceleration of 1m/s2, the value of k = 1.

Therefore, F = ma.

Conservation of Momentum

Concept of system

• The part of the universe chosen for analysis is called a system.
• Everything outside the system is called an environment.
• For example, a car moving with constant velocity can be considered a system. All the forces within the car are internal forces and all forces acting on the car from the environment are external forces like friction.

Conservation of momentum

• The total momentum of an isolated system is conserved.
• Isolated system → net external force on the system is zero.
• Example: Collision of 2 balls A and B.

From Newtons 3rd law F_{AB} = -F_{BA}

\(\begin{array}{l}m_{A}\frac{V_{a}-U_{a}}{t} = m_{B}\frac{V_{b}-U_{b}}{t}\end{array} \)

\(\begin{array}{l}m_{A}U_{A} + m_{B}U_{B} = m_{A}V_{A} + m_{B}V_{B}\end{array} \)

Third Law of Motion

Newton’s 3rd law states that every action has an equal and opposite reaction. Action and reaction forces are equal, opposite and acting on different bodies.

Inertial and Non-inertial frames

• A non-inertial frame of reference is a frame of reference in which Newton’s laws of motion do not hold. A non-inertial reference frame is a frame of reference that is undergoing acceleration with respect to an inertial frame. An accelerometer at rest in a non-inertial frame will, in general, detect a non-zero acceleration.
• A frame of reference where Newton’s Laws hold is known as an inertial frame of reference.

 

 

 

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