As we look at our surroundings, we see a large
variety of things with different shapes, sizes
and textures. Everything in this universe is
made up of material which scientists have
named “matter”. The air we breathe, the food
we eat, stones, clouds, stars, plants and
animals, even a small drop of water or a
particle of sand– each thing is matter. We can
also see as we look around that all the things
mentioned above occupy space, that is,
volume* and have mass.
Since early times, human beings have
been trying to understand their surroundings.
Early Indian philosophers classified matter in
the form of five basic elements – the
“Panch Tatva”– air, earth, fire, sky and water.
According to them everything, living or nonliving,
was made up of these five basic
elements. Ancient Greek philosophers had
arrived at a similar classification of matter.
Modern day scientists have evolved two
types of classification of matter based on their
physical properties and chemical nature.
In this chapter we shall learn about
matter based on its physical properties.
Chemical aspects of matter will be taken up
in subsequent chapters.
1.1 Physical Nature of Matter
1.1.1 MATTER IS MADE UP OF PARTICLES
For a long time, two schools of thought
prevailed regarding the nature of matter. One
school believed matter to be continuous like
a block of wood, whereas, the other thought
that matter was made up of particles like
sand. Let us perform an activity to decide
about the nature of matter – is it continuous
or particulate?
Activity ______________ 1.1
• Take a 100 mL beaker.
• Fill half the beaker with water and
mark the level of water.
• Dissolve some salt/ sugar with the help
of a glass rod.
• Observe any change in water level.
• What do you think has happened to
the salt?
• Where does it disappear?
• Does the level of water change?
In order to answer these questions we
need to use the idea that matter is made up
of particles. What was there in the spoon, salt
or sugar, has now spread throughout water.
This is illustrated in Fig. 1.1.
1.1.2 HOW SMALL ARE THESE PARTICLES
OF MATTER?
Activity ______________ 1.2
• Take 2-3 crystals of potassium
permanganate and dissolve them in
100 mL of water.
Fig. 1.1: When we dissolve salt in water, the particles
of salt get into the spaces between particles
of water.
* The SI unit of volume is cubic metre (m3). The common unit of measuring volume is
litre (L) such that 1L = 1 dm3, 1L = 1000 mL, 1 mL = 1 cm3.
1
MATTER IN OUR SURROUNDINGS
Chapter
2 SCIENCE
• Take out approximately 10 mL of this
solution and put it into 90 mL of clear
water.
• Take out 10 mL of this solution and
put it into another 90 mL of clear water.
• Keep diluting the solution like this 5 to
8 times.
• Is the water still coloured ?
1.2.2 PARTICLES OF MATTER ARE
CONTINUOUSLY MOVING
Activity ______________ 1.3
• Put an unlit incense stick in a corner
of your class. How close do you have to
go near it so as to get its smell?
• Now light the incense stick. What
happens? Do you get the smell sitting
at a distance?
• Record your observations.
Activity ______________ 1.4
• Take two glasses/beakers filled with
water.
• Put a drop of blue or red ink slowly
and carefully along the sides of the first
beaker and honey in the same way in
the second beaker.
• Leave them undisturbed in your house
or in a corner in the class.
• Record your observations.
• What do you observe immediately after
adding the ink drop?
• What do you observe immediately after
adding a drop of honey?
• How many hours or days does it take
for the colour of ink to spread evenly
throughout the water?
Activity ______________ 1.5
• Drop a crystal of copper sulphate or
potassium permanganate into a glass
of hot water and another containing
cold water. Do not stir the solution.
Allow the crystals to settle at the
bottom.
• What do you observe just above the
solid crystal in the glass?
• What happens as time passes?
• What does this suggest about the
particles of solid and liquid?
• Does the rate of mixing change with
temperature? Why and how?
From the above three activities (1.3, 1.4 and
1.5), we can conclude the following:
Fig. 1.2: Estimating how small are the particles of
matter. With every dilution, though the colour
becomes light, it is still visible.
This experiment shows that just a few
crystals of potassium permanganate can
colour a large volume of water (about
1000 L). So we conclude that there must be
millions of tiny particles in just one crystal
of potassium permanganate, which keep on
dividing themselves into smaller and smaller
particles. Ultimately a stage is reached when
the particles cannot divide further into
smaller particles.
The same activity can be done using
2 mL of Dettol instead of potassium
permanganate. The smell can be detected
even on repeated dilution.
The particles of matter are very small –
they are small beyond our imagination!!!!
1.2 Characteristics of Particles of
Matter
1.2.1 PARTICLES OF MATTER HAVE SPACE
BETWEEN THEM
In activities 1.1 and 1.2 we saw that particles
of sugar, salt, Dettol, or potassium
permanganate got evenly distributed in water.
Similarly, when we make tea, coffee or
lemonade (nimbu paani ), particles of one type
of matter get into the spaces between particles
of the other. This shows that there is enough
space between particles of matter.
MATTER IN OUR SURROUNDINGS 3
• If we consider each student as a particle
of matter, then in which group the
particles held each other with the
maximum force?
Activity ______________ 1.7
• Take an iron nail, a piece of chalk and
a rubber band.
• Try breaking them by hammering,
cutting or stretching.
• In which of the above three substances
do you think the particles are held
together with greater force?
Activity ______________ 1.8
• Open a water tap, try breaking the
stream of water with your fingers.
• Were you able to cut the stream of
water?
• What could be the reason behind the
stream of water remaining together?
The above three activities (1.6, 1.7 and
1.8) suggest that particles of matter have force
acting between them. This force keeps the
particles together. The strength of this force
of attraction varies from one kind of matter
to another.
uestions
1. Which of the following are
matter?
Chair, air, love, smell, hate,
almonds, thought, cold, colddrink,
smell of perfume.
2. Give reasons for the following
observation:
The smell of hot sizzling food
reaches you several metres
away, but to get the smell from
cold food you have to go close.
3. A diver is able to cut through
water in a swimming pool. Which
property of matter does this
observation show?
4. What are the characteristics of
the particles of matter?
Particles of matter are continuously
moving, that is, they possess what we call
the kinetic energy. As the temperature rises,
particles move faster. So, we can say that with
increase in temperature the kinetic energy of
the particles also increases.
In the above three activities we observe
that particles of matter intermix on their own
with each other. They do so by getting into
the spaces between the particles. This
intermixing of particles of two different types
of matter on their own is called diffusion. We
also observe that on heating, diffusion
becomes faster. Why does this happen?
1.2.3 PARTICLES OF MATTER ATTRACT
EACH OTHER
Activity ______________ 1.6
• Play this game in the field— make four
groups and form human chains as
suggested:
• The first group should hold each other
from the back and lock arms like Bihu
dancers (Fig. 1.3).
Fig. 1.3
• The second group should hold hands
to form a human chain.
• The third group should form a chain
by touching each other with only their
finger tips.
• Now, the fourth group of students
should run around and try to break the
three human chains one by one into
as many small groups as possible.
• Which group was the easiest to break?
Why?
Q
4 SCIENCE
1.3 States of Matter
Observe different types of matter around you.
What are its different states? We can see that
matter around us exists in three different
states– solid, liquid and gas. These states of
matter arise due to the variation in the
characteristics of the particles of matter.
Now, let us study about the properties of
these three states of matter in detail.
1.3.1 THE SOLID STATE
Activity _____________ 1.9
• Collect the following articles— a pen, a
book, a needle and a piece of thread.
• Sketch the shape of the above articles
in your notebook by moving a pencil
around them.
• Do all these have a definite shape,
distinct boundaries and a fixed
volume?
• What happens if they are hammered,
pulled or dropped?
• Are these capable of diffusing into each
other?
• Try compressing them by applying
force. Are you able to compress them?
All the above are examples of solids. We
can observe that all these have a definite
shape, distinct boundaries and fixed volumes,
that is, have negligible compressibility. Solids
have a tendency to maintain their shape when
subjected to outside force. Solids may break
under force but it is difficult to change their
shape, so they are rigid.
Consider the following:
(a) What about a rubber band, can it
change its shape on stretching? Is it
a solid?
(b) What about sugar and salt? When
kept in different jars these take the
shape of the jar. Are they solid?
(c) What about a sponge? It is a solid
yet we are able to compress it. Why?
All the above are solids as:
• A rubber band changes shape under
force and regains the same shape when
the force is removed. If excessive force is
applied, it breaks.
• The shape of each individual sugar or
salt crystal remains fixed, whether we
take it in our hand, put it in a plate or in
a jar.
• A sponge has minute holes, in which
air is trapped, when we press it, the air
is expelled out and we are able to
compress it.
1.3.2 THE LIQUID STATE
Activity _____________1.10
• Collect the following:
(a) water, cooking oil, milk, juice, a
cold drink.
(b) containers of different shapes. Put
a 50 mL mark on these containers
using a measuring cylinder from
the laboratory.
• What will happen if these liquids are
spilt on the floor?
• Measure 50 mL of any one liquid and
transfer it into different containers one
by one. Does the volume remain the
same?
• Does the shape of the liquid remain the
same ?
• When you pour the liquid from one
container into another, does it flow
easily?
We observe that liquids have no fixed
shape but have a fixed volume. They take up
the shape of the container in which they are
kept. Liquids flow and change shape, so they
are not rigid but can be called fluid.
Refer to activities 1.4 and 1.5 where we
saw that solids and liquids can diffuse into
liquids. The gases from the atmosphere
diffuse and dissolve in water. These gases,
especially oxygen and carbon dioxide, are
essential for the survival of aquatic animals
and plants.
All living creatures need to breathe for
survival. The aquatic animals can breathe
under water due to the presence of dissolved
oxygen in water. Thus, we may conclude that
solids, liquids and gases can diffuse into
liquids. The rate of diffusion of liquids is
MATTER IN OUR SURROUNDINGS 5
higher than that of solids. This is due to the
fact that in the liquid state, particles move
freely and have greater space between each
other as compared to particles in the solid
state.
1.3.3 THE GASEOUS STATE
Have you ever observed a balloon seller filling
a large number of balloons from a single
cylinder of gas? Enquire from him how many
balloons is he able to fill from one cylinder.
Ask him which gas does he have in the cylinder.
Activity _____________1.11
• Take three 100 mL syringes and close
their nozzles by rubber corks, as
shown in Fig.1.4.
• Remove the pistons from all the
syringes.
• Leaving one syringe untouched, fill
water in the second and pieces of chalk
in the third.
• Insert the pistons back into the
syringes. You may apply some vaseline
on the pistons before inserting them
into the syringes for their smooth
movement.
• Now, try to compress the content by
pushing the piston in each syringe.
We have observed that gases are highly
compressible as compared to solids and
liquids. The liquefied petroleum gas (LPG)
cylinder that we get in our home for cooking
or the oxygen supplied to hospitals in
cylinders is compressed gas. Compressed
natural gas (CNG) is used as fuel these days
in vehicles. Due to its high compressibility,
large volumes of a gas can be compressed
into a small cylinder and transported easily.
We come to know of what is being cooked
in the kitchen without even entering there,
by the smell that reaches our nostrils. How
does this smell reach us? The particles of the
aroma of food mix with the particles of air
spread from the kitchen, reach us and even
farther away. The smell of hot cooked food
reaches us in seconds; compare this with the
rate of diffusion of solids and liquids. Due to
high speed of particles and large space
between them, gases show the property of
diffusing very fast into other gases.
In the gaseous state, the particles move
about randomly at high speed. Due to this
random movement, the particles hit each
other and also the walls of the container. The
pressure exerted by the gas is because of this
force exerted by gas particles per unit area
on the walls of the container.
Fig. 1.4
• What do you observe? In which case
was the piston easily pushed in?
• What do you infer from your
observations?
Fig.1.5: a, b and c show the magnified schematic
pictures of the three states of matter. The
motion of the particles can be seen and
compared in the three states of matter.
6 SCIENCE
1.4.1 EFFECT OF CHANGE OF TEMPERATURE
Activity _____________1.12
• Take about 150 g of ice in a beaker and
suspend a laboratory thermometer so
that its bulb is in contact with the ice,
as in Fig. 1.6.
uestions
1. The mass per unit volume of a
substance is called density.
(density = mass/volume).
Arrange the following in order of
increasing density – air, exhaust
from chimneys, honey, water,
chalk, cotton and iron.
2. (a) Tabulate the differences in
the characterisitcs of states
of matter.
(b) Comment upon the following:
rigidity, compressibility,
fluidity, filling a gas
container, shape, kinetic
energy and density.
3. Give reasons
(a) A gas fills completely the
vessel in which it is kept.
(b) A gas exerts pressure on the
walls of the container.
(c) A wooden table should be
called a solid.
(d) We can easily move our hand
in air but to do the same
through a solid block of wood
we need a karate expert.
4. Liquids generally have lower
density as compared to solids.
But you must have observed that
ice floats on water. Find out why.
1.4 Can Matter Change its State?
We all know from our observation that water
can exist in three states of matter–
• solid, as ice,
• liquid, as the familiar water, and
• gas, as water vapour.
What happens inside the matter during
this change of state? What happens to the
particles of matter during the change of
states? How does this change of state take
place? We need answers to these questions,
isn’t it?
Q
(a)
(b)
Fig. 1.6: (a) Conversion of ice to water, (b) conversion
of water to water vapour
MATTER IN OUR SURROUNDINGS 7
• Start heating the beaker on a low flame.
• Note the temperature when the ice
starts melting.
• Note the temperature when all the ice
has converted into water.
• Record your observations for this
conversion of solid to liquid state.
• Now, put a glass rod in the beaker and
heat while stirring till the water starts
boiling.
• Keep a careful eye on the thermometer
reading till most of the water has
vaporised.
• Record your observations for the
conversion of water in the liquid state
to the gaseous state.
On increasing the temperature of solids,
the kinetic energy of the particles increases.
Due to the increase in kinetic energy, the
particles start vibrating with greater speed.
The energy supplied by heat overcomes the
forces of attraction between the particles. The
particles leave their fixed positions and start
moving more freely. A stage is reached when
the solid melts and is converted to a liquid.
The temperature at which a solid melts to
become a liquid at the atmospheric pressure
is called its melting point.
The melting point of a solid is an
indication of the strength of the force of
attraction between its particles.
The melting point of ice is 273.16 K*. The
process of melting, that is, change of solid
state into liquid state is also known as fusion.
When a solid melts, its temperature
remains the same, so where does the heat
energy go?
You must have observed, during the
experiment of melting, that the temperature
of the system does not change after the
melting point is reached, till all the ice melts.
This happens even though we continue to
heat the beaker, that is, we continue to supply
heat. This heat gets used up in changing the
state by overcoming the forces of attraction
between the particles. As this heat energy is
absorbed by ice without showing any rise in
temperature, it is considered that it gets
hidden into the contents of the beaker and is
known as the latent heat. The word latent
means hidden. The amount of heat energy
that is required to change 1 kg of a solid into
liquid at atmospheric pressure at its melting
point is known as the latent heat of fusion.
So, particles in water at 00 C (273 K) have
more energy as compared to particles in ice
at the same temperature.
When we supply heat energy to water,
particles start moving even faster. At a certain
temperature, a point is reached when the
particles have enough energy to break free
from the forces of attraction of each other. At
this temperature the liquid starts changing
into gas. The temperature at which a liquid
starts boiling at the atmospheric pressure is
known as its boiling point. Boiling is a bulk
phenomenon. Particles from the bulk of the
liquid gain enough energy to change into the
vapour state.
For water this temperature is 373 K
(100 0C = 273 + 100 = 373 K).
Can you define the latent heat of
vaporisation? Do it in the same way as we
have defined the latent heat of fusion.
Particles in steam, that is, water vapour at
373 K (1000 C) have more energy than water
at the same temperature. This is because
particles in steam have absorbed extra energy
in the form of latent heat of vaporisation.
*Note: Kelvin is the SI unit of temperature, 00 C =273.16 K. For convenience, we take 00 C = 273 K
after rounding off the decimal. To change a temperature on the Kelvin scale to the Celsius scale
you have to subtract 273 from the given temperature, and to convert a temperature on the
Celsius scale to the Kelvin scale you have to add 273 to the given temperature.
So, we infer that the state of matter can
be changed into another state by changing
the temperature.
We have learnt that substances around
us change state from solid to liquid and from
liquid to gas on application of heat. But there
8 SCIENCE
closer? Do you think that increasing or
decreasing the pressure can change the state
of matter?
are some that change directly from solid state
to gaseous state and vice versa without
changing into the liquid state.
Activity _____________1.13
• Take some camphor or ammonium
chloride. Crush it and put it in a china
dish.
• Put an inverted funnel over the china
dish.
• Put a cotton plug on the stem of the
funnel, as shown in Fig. 1.7.
* atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa):
1 atmosphere = 1.01 × 105 Pa. The pressure of air in atmosphere is called atmospheric pressure. The
atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure.
Fig. 1.7: Sublimation of ammonium chloride
Fig. 1.8: By applying pressure, particles of matter
can be brought close together.
Applying pressure and reducing
temperature can liquefy gases.
Have you heard of solid carbon dioxide
(CO2)? It is stored under high pressure. Solid
CO2 gets converted directly to gaseous state
on decrease of pressure to 1 atmosphere*
without coming into liquid state. This is the
reason that solid carbon dioxide is also known
as dry ice.
Thus, we can say that pressure and
temperature determine the state of a
substance, whether it will be solid, liquid
or gas.
• Now, heat slowly and observe.
• What do you infer from the above
activity?
A change of state directly from solid to
gas without changing into liquid state (or vice
versa) is called sublimation.
1.4.2 EFFECT OF CHANGE OF PRESSURE
We have already learnt that the difference in
various states of matter is due to the
difference in the distances between the
constituent particles. What will happen when
we start putting pressure and compress a gas
enclosed in a cylinder? Will the particles come Fig. 1.9: Interconversion of the three states of matter
MATTER IN OUR SURROUNDINGS 9
dish and keep it inside a cupboard or
on a shelf in your class.
• Record the room temperature.
• Record the time or days taken for the
evaporation process in the above cases.
• Repeat the above three steps of activity
on a rainy day and record your
observations.
• What do you infer about the effect of
temperature, surface area and wind
velocity (speed) on evaporation?
You must have observed that the rate of
evaporation increases with–
• an increase of surface area:
We know that evaporation is a surface
phenomenon. If the surface area is
increased, the rate of evaporation
increases. For example, while putting
clothes for drying up we spread them out.
• an increase of temperature:
With the increase of temperature, more
number of particles get enough kinetic
energy to go into the vapour state.
• a decrease in humidity:
Humidity is the amount of water vapour
present in air. The air around us cannot
hold more than a definite amount of
water vapour at a given temperature. If
the amount of water in air is already high,
the rate of evaporation decreases.
• an increase in wind speed:
It is a common observation that clothes
dry faster on a windy day. 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.
1.5.2 HOW DOES EVAPORATION CAUSE
COOLING?
In an open vessel, the liquid keeps on
evaporating. The particles of liquid absorb
energy from the surrounding to regain the
energy lost during evaporation. This
absorption of energy from the surroundings
make the surroundings cold.
uestions
1. Convert the following temperature
to celsius scale:
a. 300 K b. 573 K.
2. What is the physical state of
water at:
a. 250ºC b. 100ºC ?
3. For any substance, why does the
temperature remain constant
during the change of state?
4. Suggest a method to liquefy
atmospheric gases.
1.5 Evaporation
Do we always need to heat or change pressure
for changing the state of matter? Can you
quote some examples from everyday life where
change of state from liquid to vapour takes
place without the liquid reaching the boiling
point? Water, when left uncovered, slowly
changes into vapour. Wet clothes dry up.
What happens to water in the above two
examples?
We know that particles of matter are
always moving and are never at rest. At a
given temperature in any gas, liquid or solid,
there are particles with different amounts of
kinetic energy. In the case of liquids, a small
fraction of particles at the surface, having
higher kinetic energy, is able to break away
from the forces of attraction of other particles
and gets converted into vapour. This
phenomenon of change of a liquid into
vapours at any temperature below its boiling
point is called evaporation.
1.5.1 FACTORS AFFECTING EVAPORATION
Let us understand this with an activity.
Activity _____________1.14
• Take 5 mL of water in a test tube and
keep it near a window or under a fan.
• Take 5 mL of water in an open china
dish and keep it near a window or
under a fan.
• Take 5 mL of water in an open china
Q
10 SCIENCE
What happens when you pour some
acetone (nail polish remover) on your palm?
The particles gain energy from your palm or
surroundings and evaporate causing the
palm to feel cool.
After a hot sunny day, people sprinkle
water on the roof or open ground because
the large latent heat of vaporisation of water
helps to cool the hot surface.
Can you cite some more examples from
daily life where we can feel the effect of cooling
due to evaporation?
Why should we wear cotton clothes in
summer?
During summer, we perspire more
because of the mechanism of our body which
keeps us cool. We know that during
evaporation, the particles at the surface of
the liquid gain energy from the surroundings
or body surface and change into vapour. The
heat energy equal to the latent heat of
vaporisation is absorbed from the body
leaving the body cool. Cotton, being a good
absorber of water helps in absorbing the
sweat and exposing it to the atmosphere for
easy evaporation.
Why do we see water droplets on the outer
surface of a glass containing ice-cold
water?
Let us take some ice-cold water in a
tumbler. Soon we will see water droplets on
the outer surface of the tumbler. The water
vapour present in air, on coming in contact
with the cold glass of water, loses energy and
gets converted to liquid state, which we see
as water droplets.
uestions
1. Why does a desert cooler cool
better on a hot dry day?
2. How does the water kept in an
earthen pot (matka) become cool
during summer?
3. Why does our palm feel cold
when we put some acetone or
petrol or perfume on it?
4. Why are we able to sip hot tea or
milk faster from a saucer rather
than a cup?
5. What type of clothes should we
wear in summer?
More to know
Now scientists are talking of five states of matter: Solid, Liquid, Gas, Plasma and
Bose-Einstein Condensate.
Plasma: The state consists of super energetic and super excited particles. These
particles are in the form of ionised gases. The fluorescent tube and neon sign bulbs
consist of plasma. Inside a neon sign bulb there is neon gas and inside a fluorescent
tube there is helium gas or some other gas. The gas gets ionised, that is, gets charged
when electrical energy flows through it. This charging up creates a plasma glowing
inside the tube or bulb. The plasma glows with a special colour depending on the
nature of gas. The Sun and the stars glow because of the presence of plasma in
them. The plasma is created in stars because of very high temperature.
Bose-Einstein Condensate: In 1920, Indian physicist Satyendra Nath Bose had
done some calculations for a fifth state of matter. Building on his calculations, Albert
Einstein predicted a new state of matter – the Bose-
Einstein Condensate (BEC). In 2001, Eric A. Cornell,
Wolfgang Ketterle and Carl E. Wieman of USA received
the Nobel prize in physics for achieving “Bose-Einstein
condensation”. The BEC is formed by cooling a gas of
extremely low density, about one-hundred-thousandth
the density of normal air, to super low temperatures.
You can log on to www.chem4kids.com to get more
information on these fourth and fifth states of matter.
Q
S.N. Bose
(1894-1974)
Albert Einstein
(1879-1955)
MATTER IN OUR SURROUNDINGS 11
What
you have
learnt
• Matter is made up of 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 each other while for gases, there is 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 going through liquid state, and vice versa.
• Boiling is a bulk phenomenon. Particles from the bulk (whole)
of the liquid change into vapour state.
• Evaporation is a surface phenomenon. Particles from the
surface gain enough energy to overcome the forces of attraction
present in the liquid and change into the vapour state.
• The rate of evaporation depends upon the surface area exposed
to the atmosphere, the temperature, the humidity and the
wind speed.
• Evaporation causes cooling.
• Latent heat of vaporisation is the heat energy required to change
1 kg of a liquid to gas at atmospheric pressure at its boiling
point.
• Latent heat of fusion is the amount of heat energy required to
change 1 kg of solid into liquid at its melting point.
12 SCIENCE
Exercises
1. Convert the following temperatures to the Celsius scale.
(a) 300 K (b) 573 K.
2. Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C.
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any
solid.
(b) We can get the smell of perfume sitting several metres away.
4. Arrange the following substances in increasing order of forces
of attraction between the particles— water, sugar, oxygen.
5. What is the physical state of water at—
(a) 25°C (b) 0°C (c) 100°C ?
6. Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
7. Why is ice at 273 K more effective in cooling than water at the
same temperature?
8. What produces more severe burns, boiling water or steam?
9. Name A,B,C,D,E and F in the following diagram showing change
in its state
Quantity Unit Symbol
Temperature kelvin K
Length metre m
Mass kilogram kg
Weight newton N
Volume cubic metre m3
Density kilogram per cubic metre kg m–3
Pressure pascal Pa
• Some measurable quantities and their units to remember:
MATTER IN OUR SURROUNDINGS 13
Group Activity
Prepare a model to demonstrate movement of particles in solids,
liquids and gases.
For making this model you will need
• A transparent jar
• A big rubber balloon or piece of stretchable rubber sheet
• A string
• Few chick-peas or black gram or dry green peas.
How to make?
• Put the seeds in the jar.
• Sew the string to the centre of the rubber sheet and put some
tape to keep it tied securely.
• Stretch and tie the rubber sheet on the mouth of the jar.
• Your model is ready. Now run your fingers up and down the
string by first tugging at it slowly and then rapidly.
Fig. 1.10: A model for happy converting of solid to liquid and liquid to gas.
