HPE-book-5-for-press

g. Write the name of any two sublimates.

6. Define the following.

a. Molecules b. Atoms c. Evaporation

d. Condensation e. Sublimation

7. Differentiate between :

a. Melting and sublimation

b. Evaporation and condensation

8. Draw a well labelled diagram to show the process of sublimation.

Project work

Make a list of the matters that you use in a day. Classify them into solid, liquid
and gas.

Science, Health and Physical Education Book - 5 97

9Lesson Energy

Specific After the completion of the lesson, students will be able to:
Objectives • define energy and its types.
• differentiate between renewable and non-renewable sources of

energy with examples.
• explain various forms of energy.
• describe the major sources of energy.
• write about energy crisis and explain the methods to solve it.

Mind Opener

Name the form of energy that is possessed by the following things.

98 Science, Health and Physical Education Book - 5

Introduction

In our daily life, energy is the most important factor. We need energy to
perform various kinds of activities.

Living things move, eat, sleep, laugh, respire and do a lot of things. For all
these, they need energy. So we can say energy is the ability to do work. Work
can be done by a glowing bulb, moving body, stretched string, etc. Similarly,
when we get hungry, we eat food. This food is converted into energy and we
can do work. Energy is essential to perform different types of activities.

Even to perform the work by machine, it requires energy. Usually, machines
get energy from fuels. An aeroplane needs fuel to fly. A lamp needs kerosene
oil to give out light. A fire needs coal or wood to burn. All these things need
fuels. Coal, oil and gas are all fuels. They are used to provide energy. They are
called resources. We get them from the earth.

There are different sources of energy. The sun is the ultimate source of light
and heat energy. Cell, battery, etc are the sources of electrical energy. Television,
radio, loudspeaker, etc are the sources of sound energy. Burning of certain
substances gives heat. Therefore, burning coal, is the source of heat energy.
Petrol, diesel, etc are the sources of chemical energy. The substances from
which we get energy are called sources of energy. The sources of energy can
be divided into two types and they are renewable sources of energy and non-
renewable sources of energy

a. Renewable sources of energy

The sources of energy which can Hydropower Solar energy
be replaced immediately after
their use and can be used again
and again are called renewable
sources of energy. Sun, wind,
water, agricultural residue, bio
gas, etc are some of the renewable
sources of energy.

Science, Health and Physical Education Book - 5 99

b. Non-renewable sources of energy

The sources of energy which cannot be replaced after their use, get exhausted
and cannot be used again and again are called non-renewable sources of
energy. Coal, petrol, diesel, petroleum products, natural gas, etc are some of
the non-renewable sources of energy. These sources of energy are in limited
amount in nature and take many years to form once again. Hence, they get
exhausted and cannot be used again and again.

Petroleum LP gas Coal

Activity

Identify the different sources of energy around your locality and write
them under the headings provided below on the table.

S.N. Renewable Non-renewable

Forms of Energy

There are different forms of energy. We use energy in different forms to do
different works. Heat energy, light energy, electrical energy, sound energy,
magnetic energy, etc are forms of energy.

a. Heat Energy

Heat is the one of the most important forms of energy. The form of energy
which gives the sensation of warmth to us is called heat energy. The sun is the
main source of heat on the earth. We get heat energy by burning substances
like wood, coal, oil, fuel, gases, etc. This energy is useful in cooking, drying

100 Science, Health and Physical Education Book - 5

clothes, running vehicles, operating machines in industries, etc. Heat also
brings the change in the state of object.

Sun Fire Electric heater

b. Light Energy

Light is a form of energy which gives sensation of vision to our eyes. Light
energy is produced from extremely hot objects like bulbs, the sun, burning
candles, etc. Light energy is very essential. All the green plants absorb the
light energy from the sun and prepare their own food by the process of
photosynthesis. Besides, some solar vehicles are run by using sunlight.

Bulb Candle Sun

c. Electrical Energy

Electrical energy is the most important Info bits

form of energy for today's world. The various forms of energy are

This form of energy is obtained from inter convertible, which means

photocell, cell, battery, dynamo or that one form of energy can be

generator. It can also be produced by changed into another form.

using the energy of flowing water. It is

also called hydroelectricity. In our country, hydroelectricity is the main source

of electricity.

Electricity is used to obtain heat and light. It is used to run electrical appliances

Science, Health and Physical Education Book - 5 101

like washing machine, television, computer, vacuum cleaner, air conditioners,
tubelights, radio, fans, etc. Similarly, it is used to run various engines and
devices in factories and industries.

Electricity can be produced from the solar energy with the help of solar panels.
Electrical energy can be changed into other forms of energy as heat, light,
sound, etc.

Generator Battery Hydropower

Activity

Visit a hydroelectricity power house or watch the animated video to
observe the process of generating hydroelectricity.

d. Sound Energy

Sound is a form of energy which produces the sensation of hearing in our
ears. Sound is produced due to the vibration of the particles of a body. It is
transferred from a vibrating object and carried through the air to our ears.
We can make sounds by making things vibrate. Vibration means shaking up
and down or backwards and forwards very fast. There are different kinds of
sounds. They can be high or low. High sounds are made by fast vibrations and
low sounds are made by slow vibrations. Most sounds we hear travel through
the air. Temple bell, television, radio, musical instruments, loudspeakers, etc
are some sources of sound.

Temple bell Harmonium Radio

102 Science, Health and Physical Education Book - 5

e. Magnetic Energy

The energy that is obtained from a magnet is called magnetic energy. A magnet
is a substance which attracts magnetic substances. A magnet is used in many
sound producing devices like electric bell, radio, television, mobile, phone,
etc. It is also used in motors, generators and other electrical equipments.

Similarly, heavy magnetic substances can be lifted with the help of large
magnets in the industries. Electrical energy can be produced from magnetic
energy. Magnet can also be used to separate non-magnetic substances and
magnetic substances from their mixture. It is used in hospitals to remove iron
dust from the eyes. A magnetic compass plays vital role to find the directions.
Generally, magnetic compass is used to find the directions in deserts and seas.

Bar magnet Magnetic compass Horse shoe magnet

The sun: the main source of energy

Among the different types of
energy mentioned above, the sun is
considered as the ultimate source
of energy. All the sources of energy
depend on solar energy directly or
indirectly. The earth receives heat and
light energy from the sun directly.
Green plants require light energy for
the purpose of photosynthesis and
prepare the food. All animals depend
on the green plants directly or indirectly. So, all the living things depend upon
solar energy for food. Similarly, solar energy is also necessary for the purpose
of water cycle. The heat of the sun changes the earth's water into water vapour
that forms cloud in the atmosphere and hence, rainfall takes place. The flowing

Science, Health and Physical Education Book - 5 103

of river water is necessary for the generation of hydroelectricity. Therefore,

energy obtained from running water and hydroelectricity are the outcomes of

solar energy.

Similarly, we use solar energy to operate Explore

various devices like solar water heater, Discuss the advantages of
traffic lights, vehicles, etc. The heat of using solar energy over
the sun warms up the air and causes air conventional forms of energy.
flow. Blowing of wind helps to rotate

wind mills, turbines, etc and also generate electricity in some cases. In case of

energy crisis, solar energy can be used as a only alternative sources. Hence, the

sun is considered as the main source of energy.

Energy crisis

The shortage of fuel and energy after certain period of time due to its limitation
in nature is called energy crisis. About 80% demand of total fuel necessary
to the world is being fulfilled by natural gas, coal and mineral oil. As these
are non-renewable sources of energy and are in limited amount in mines,
they are likely to be finished in the near future. Population growth, market
manipulation, careless utilization, lack of development of alternative sources
of energy are the main causes of energy crisis. The proper use and management
of such energy is known as conservation of energy.

The main way of solving the problem of energy crisis is the proper use and
management of non-renewable resources. The best possible solution is to use
alternative sources of energy and improve our conservation efforts. Some of
the ways to minimize the problems of energy crisis are.

1. Use of alternative sources of energy such as solar energy, wind energy and
biomass energy.

2. Recycle and reuse the resource as you can.
3. Hydro electricity should be generated as far as possible.
4. Use of existing sources of energy wisely and economically.
5. Uses of coal, petrol and petroleum products should be minimised.
6. Introduction and development of electrical and solar vehicles.
7. Use of biogas and bio based fuels.
8. Use of LED (Light Emitting Diode) bulbs, instead of ordinary electric

bulbs.
9. Afforestation to obtain timber and firewood regularly.

104 Science, Health and Physical Education Book - 5

Points to Remember

1. Energy is essential to perform different types of activities.
2. Energy is the capacity to do work.
3. The sources of energy which can be replaced immediately after their

use and can be used again and again are called renewable sources of
energy.
4. The sources of energy which cannot be replaced after their use,
get exhasuted and cannot be used again and again are called non
renewable sources of energy.
5. There are different forms of energy like heat energy, light energy,
sound energy, solar energy, wind energy, etc.
6. The sun is the main source of energy for life on the earth.
7. We should use alternate sources of energy to reduce energy crisis.
8. The shortage of fuel and energy after certain period of time due to its
limitation in the nature is called energy crisis.
9. The main way of solving the problem of energy crisis is the proper use
and management of non renewable resources.

Exercise

1. Choose the best answer from the given alternatives.

a. Solar and wind energy are _________.

i. non renewable ii. renewable iii. magnetic

b. Coal and oil are _________.

i. non renewable ii. renewable

ii. alternative sources of energy

c. The vibration of the particles produce _________.

i. wind ii. sound iii. light iv. coal

d. Energy that is obtained from the magnet is known as ______ energy.

i. solar ii. light iii. magnetic iv. chemical

e. The main source of energy is the _________.

i. wind ii. water iii. sun iv. electrical

Science, Health and Physical Education Book - 5 105

f. The best way to save energy is to use

i. coal and solar ii. fossil fuel and fire wood

iii. solar and wind energy

2. Fill in the blanks with appropriate words.

a. ___________ is the capacity to do work.

b. Most of the heat and light energy on the earth comes from the ____.
c. Plants use ___________ to make their food.
d. Coal and oil are ____________sources of energy.
e. The energy of running water is used to generate ___________ .

f. ___________ is the ultimate source of energy.
g. Lack of essential energy for our use is called___________ .
h. Recycle is one of the ways to control___________ .

3. Write 'T' for true and 'F' for false statement.

a. The capacity of doing work is called energy.
b. Fossil fuels like coal, petrol, diesel, etc are renewable sources of

energy.
c. The sun is the main source of energy.
d. A type of energy does not change into another type.

e. We should not use wind energy as the source of energy.
f. Solar appliances use energy formed by running water.
g. A compass is used to detect direction.
h. Future problem of shortage of sources of energy is called energy

crisis.

4. Match the followings:

Heat energy sensation of vision

Light energy produced due to vibration of particle

Electrical energy produced by magnets

Sound energy sensation of warmth

Magnetic energy main source of energy

Solar energy lighting bulb

5. Answer the following questions:

a. Define energy. How is energy classified?
b. What is the difference between renewable and non-renewable source

106 Science, Health and Physical Education Book - 5

of energy? Give two examples of each.

c. Define heat energy. Name two sources of heat energy.

d. What is light energy? Name two sources of light energy.

e. What kind of vibration causes low sounds?

f. What is solar energy? List the useful ways of solar energy.

g. What is energy crisis?

h. What alternate uses of energy can be used in your locality?

i. List five ways by which you can save energy at home.

6. Give reasons of following:

a. Coal is a non-renewable source of energy.

b. Solar and wind energy are renewable sources of energy.

c. We should conserve non renewable sources of energy.

d. Sun is the ultimate source of energy.

7. Write short notes on:

a. Light energy b. Sound energy

c. Electrical energy d. Magnetic energy

Think and Discuss

• Why should solar panels face toward the sun?
• What would happen if the sun stopped shining?

Life skills

Prepare a report and present it to your teacher. The report should show the ways
and methods to conserve electrical energy. Also suggest how you think electricity
can be conserved in homes and schools.

Project work

• Make a model of any one of the alternative source of energy.
• Draw two musical instruments that make sounds using strings.
• Prepare a list of various forms of energy. Also, write down their

applications in our daily life.
• Collect various picture of sources of heat energy and paste them in your

scrapbook.

Science, Health and Physical Education Book - 5 107

10Lesson Weather

Specific After the completion of the lesson, students will be able to :
Objectives • define weather and climate.
• explain various factors affecting weather.
• list some ways to forecast weather.
• explain the process of formation of cloud.
• identify different types of clouds.

Mind Opener

Answer the following questions:
• Are you feeling hot or cold now?
• Name the conditions that affect the weather of a place.
• Have you ever seen any instruments that are used to get

information of weather forecasting? Draw a picture of anyone.
• Identify the weather from the following pictures.

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Introduction

Is it cloudy, windy, sunny or rainy today? The answer to this question gives us
about weather of your place. Sometimes it is very sunny and soon the clouds
cover the sky and it starts to rain. At the same time in the higher altitudes, it
starts to snow. Thus, weather is the state of the atmosphere at a place and time
in relation to wind, temperature, rain, etc. Weather does not remain the same.
Sometime it is cloudy and sometime it is quite sunny. Some days are very hot
and some days are foggy and cold. Weather even changes many times within a
day. When you go to school the weather may be sunny, it may be cloudy during
your lunch time and it may rain while coming from school. Thus, weather
changes from time to time or from hour to hour and every day. The daily
changes in the weather are due to winds, clouds, rainfall, humidity, sunlight
etc. The seasonal changes in weather are due to revolution of the earth around
the sun. The science that deals with the study of weather is called meteorology
and the person who studies weather is called a meteorologist.

It is essential to know about the weather outside because it affects our daily
activities. We must be careful not to go outside during a storm. We must use
an umbrella or wear a raincoat when we have to go out in the rain.

Climate is the average atmospheric condition over a long period of time.
Usually it is for more than 30 years. It does not change like weather but is
different in different region. In our country, Himalayan region has very cold
climate whereas Terai region has hot climate. Hilly region has moderate type of
climate. Thus, the climate of a place is affected by its altitude, terrain, latitude
as well as aquatic mass and their occurance. Similarly, the surface near the
equator has a hot climate because it gets sunshine from the sun almost directly
overhead. Far away from the equator, the climate is always cold.

The variation in plants and animals is due to the climatic condition of a
particular place. For example, the animals found in Himalayan region have
long hair or fur but the animals of Hilly and Terai region have short hair or fur.
Furthermore, the vegetation of these region also differ from each other.

Science, Health and Physical Education Book - 5 109

Activity 1

Observe the condition of weather in the morning, afternoon and evening
for a week. What change in weather do you notice? Observe carefully and
complete the given table.

Date Day Morning Afternoon Evening
(waking up) (During lunch (During
dinner)
break)

Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday

What can you conclude from this activity?

Factors causing changes in weather and climate

Weather is the general condition of air around us. Weather conditions change
very frequently even within a day. In most places, weather can change hour
to hour, day-to-day and season- to-season. The changes in weather are caused
mainly by the sun, monsoon, water cycle, humidity, etc.

1. The Sun

The sun is the most
important factor that
brings changes in weather.
It is the heat of the sun,
which causes wind to
blow and clouds to form.
The sun causes difference
in temperature. It is hot
during the day when the
sun shines. In the same way, night is cooler than the day due to lack of heat
from the sun. Similarly, there is difference in temperature in the morning, noon

110 Science, Health and Physical Education Book - 5

and evening. The rays of the sun are slanting in the morning and evening.
Therefore, morning and evening are cooler. At the noon, the sun is directly
above our head. Its rays fall straight on the earth. Thus, it is comparatively
hotter in the afternoon.

Winters are cold and summers are hot. The earth revolves around an elliptical
path called orbit. At the same time, it rotates around rotational axis. The earth
is tilted at an angle of 66.5o on its axis. So, one region of the earth always
remains closer to the sun. When the sunrays fall directly on the region, it is
hot and the places where the sunrays fall slanting, it is cold. So, some days
are hot and sunny with long hours of day light while some days are cold and
daylight hours are short. These hot days makes summer. Similarly, the other
part of the earth remains far from the sun and hence it gets less sunlight and
for a shorter time. So, it is cold in this region which makes winter. In such a
way, the position of the earth and the sun brings about the changes in weather
and climate.

2. Monsoon

Monsoon is another major factor that
brings change in weather. The wind
carrying water vapour or air from
Bay of Bengal is called monsoon. It
lasts for few months. It is the cause of
rainy season in some region. During
hot summer, the wind from the Bay of
Bengal rushes toward the lands, which
is full of water vapour. It forms clouds
and causes heavy rainfall in south Asia. The monsoon generally starts from
last of May or first of June in Nepal. But, time of monsoon is being changed
due to climate change. Nepal is an agricultural country and water is needed
for crops. Therefore, monsoon season is very important for the farmers.

3. Water cycle

Water evaporates continuously from the surface of seas, rivers, lakes and from
plants and trees growing on land. The water cycle begins with evaporation of
water from those water bodies. The water vapour becomes warm, lighter and
rises in the air. The water vapour goes higher up in the sky and get mixed with
cold air and forms clouds. When water vapour is cooled sufficiently, it condenses

Science, Health and Physical Education Book - 5 111

into droplets of water, which
gather together, become heavy
and the air cannot hold it no
longer. The water falls from the
sky in the form of rain, snow,
hail, etc. This process is called
precipitation. After being used
in various ways, water finally
finds its way back into rivers
and seas, thus completing the cycle. In this way, water is never really lost from
the earth and its atmosphere. This circulation of water from the earth's surface
to the sky and back to the earth is called the water cycle. Part of the rain water
seeps into the earth's crust and penetrates the soil till it reaches a layer of rocks
that cannot be entered. This water may reappear as a spring or may be brought
to the surface when a well is dug into the ground. Water cycle is also called
hydrological cycle. Thus, the water cycle is a factor that brings about changes
in weather.

4. Humidity

The air contains water vapour. The amount of water vapour that air contains
is called humidity. The heat of the sun makes the water to mix in the air in the
form of water vapour. Humidity varies with temperature. Warm air can carry
more water vapour than cold air. That is why, in some hot places, it is very
humid. At humid places, your skin feels sticky. There is so much water vapour
in the air that your sweat cannot evaporate. The air with less water vapour is
called dry air whereas the air with more water vapour is called humid air. The
more humidity causes the rain, therefore, humidity is one of the important
factors that brings changes in weather.

Weather forecasting

Have you ever listen to the news of weather forecasting ? Do you read any
news of weather reporting? Can you tell how do they collect such type of
information? They forecast the weather by the study of various elements of
weather like rainfall, temperature, pressure, humidity, clouds, etc.

Weather forecasting is the process of predicting the weather. To forecast the
weather, the meteorologists collect the information about weather from the
ground instruments such as barometer, hydrometer, rain guaze etc. Weather

112 Science, Health and Physical Education Book - 5

affects our lives in several ways.
It affects our food, drinks,
clothing, way of recreation and
work. It affects on agriculture,
industry, transportation and
communication as well. The
knowledge of weather helps us
to plan our tasks or make many
important decisions in our daily
life. By studying the earth's
atmosphere, meteorologists can predict what the weather will be. Even we can
guess the weather by observing and analyzing the atmospheric conditions like
the motion of air and clouds in the sky in some instants. Even though they are
not perfect and accurate, some of the indicators of weather are as follows:
1. A hot shiny morning in the rainy season implies the probability of rain in

the afternoon.
2. A sudden increase in temperature may cause rain.
3. If it is cloudy since morning, it may not rain in the day.
4. If the sky is covered with black clouds suddenly, it may rain heavily.
5. In the context of our country, if the cloud moves towards the east, from the

west at the end of the rainy season, raining stops after a few days.
Nowadays, meteorological services are used by many people like farmers,
game organizers, even scientists plan their work. Similarly, modern air crafts,
military operations, even important games and outings take due consideration
of the meteorological reports. Therefore, fair knowledge of weather is not only
useful but also essential.

Science, Health and Physical Education Book - 5 113

In Nepal, there are meteorological laboratories in different parts of the country
to study weather and the factors responsible for changes in weather. With the
help of this study, meteorologists predict how the weather is going to change.
Nowadays, weather satellites which revolve around the earth, take pictures.
From those pictures, observing the condition and speed of clouds, weather is
forecasted. In the same way, weather can also be forecasted with the help of
balloon and weather maps. This type of forecasting are more reliable.

A meteorologist uses several instruments to predict the weather conditions
which are briefly described here.

1. Rain gauze: Rain gauze is a metallic instrument which is used to
measure the amount of rainfall. It is made of a copper cylinder
with a metal funnel of 5 inch in diameter. It leads into a smaller
copper container of a glass bottle, where the rain water is
accumulated. The measurement of rainfall is done by removing
the funnel and pouring the rain water into graduated cylinder of
1/2 inch diameter.

2. Barometer: Barometer is used to measure
atmospheric pressure. A mercury barometer is
made up of one metre long glass tube. Its one end
is opened and other is closed. It is adjusted upside
down into a container containing mercury. The
glass tube has mercury column, the height of which
varies according to the change in the pressure of air.
Nowadays, aneroid barometer is also used which measures the pressure
more accurately. Any liquid can be used in it.

3. Maximum - minimum thermometer: Maximum minimum
thermometer is used to record the maximum and minimum
temperature of a day. It is made of a U-shaped glass tube
having two bulbs at its two ends.

4. Hygrometer: The moisture content in the atmosphere is measured
using an instrument called hygrometer. It is also known as dry and wet
thermometer. It is a pair of simple thermometers. The bulb of one of them

114 Science, Health and Physical Education Book - 5

is placed in water or wicked with water. It is called wet
thermometer. The bulb of the other thermometer is
left in air. It is called dry thermometer. The difference
of readings between them is used to calculate relative
humidity.

5. Wind vanes: The direction of the wind is
measured by using wind vanes. It has fixed
indicators for direction and a rotator indicator,
which indicates the direction of the wind.

6. Anemometer: The speed of wind is measured
by using an anemometer. An anemometer
consists of 3 or 4 semi circular cups. They are
attached to the ends of the horizontal spokes
mounted on a high vertical mast, which is
connected with an electrically operated dial.
When the horizontal spokes rotate, the vertical
mast also moves and the dial shows the speed
of the wind.

While using those instruments, rain gauze and anemometer are placed on
the open air space while the hygrometer and maximum and minimum
thermometer are placed in the shade. Using all these instruments, we can
easily find out the following things.

a. Maximum temperature of the day.
b. Minimum temperature of the day.
c. Content of the water vapour in the air (humidity).
d. Direction of the movement of the air.
e. Speed of the air.

Activity

Listen to the radio or watch television every morning for one week to
know about the weather. Discuss with your friends in the classroom.

Science, Health and Physical Education Book - 5 115

Cloud and its formation

In nature, water exists in three different
forms. They are solid, liquid and gas. In solid
state, water is found in the Himalayan region
in the form of ice. The liquid state of water is
found in the rivers, streams, lakes, seas, etc.
Similarly, water vapour is the gaseous form
of water. When the water vapour changes
back to water droplets in the atmosphere, then cloud is formed. So, a grey
or white mass made up of very small droplets of water floating in the sky is
called cloud.

The water present in the oceans, rivers, lakes, ponds, etc evaporates due to the
heat of the sun and gets converted into vapour. The water vapour mixes with
the dust particles and undergoes condensation when air becomes cool enough.

As a result of this, cloud is formed in the atmosphere. The droplets of water in
the cloud are so small that a million of them combine to form a single raindrop.
This is the reason why cloud floats in the air.

Since the clouds are light, they are easily carried away from one place to
another by wind. Due to their movement, they change their shapes. Sometime,
the clouds may cause rainfall also.

Types of cloud

On the basis of appearance and the altitude in the sky where they are formed,
clouds are classified into four types.

1. Cirrus: Cirrus is a light cloud that is formed
above 6000 metres in the atmosphere. It looks
like curls of white hairs. It is thin and appears
like small pieces of cotton wool spread in
the atmosphere. Because of its thin size, this
cloud does not block sunlight. This is very
cold because it is made of tiny crystals of ice.
Thickening of cirrus clouds could cause light rain or hails, snowfall
within one or two days.

116 Science, Health and Physical Education Book - 5

2. Cumulus: Cumulus cloud is a thick white cloud
that lies below the cirrus and look like the shape
of cauliflower. It has flat base and generally
formed at the altitude of 5000 m to 6000 m from
the surface of the earth. It is formed in sunny
days from the pockets of rising air. Its upper
part appears bright due to sunlight and its lower
part appears dark black. When cumulus clouds
are thick, they can block sunlight casting the shadows on the surface of the
earth.

If the cumulus builds into the middle or high segment of the atmosphere,
it is called cumulonimbus. It is also the fusion of cumulus and nimbus.
When the clouds grow upward, they form very thick mass of clouds that
can cause lightening, hail stones, heavy rains, etc.

3. Stratus: Stratus cloud is thin and greyish
that spread in thin layers. It looks like a flat
blanket and is formed at an altitude of 500 m to
3000 m of earth's atmosphere. It spreads across
the whole sky in the form of thin white layers.
These clouds are generally seen when wind does
not move during morning and evening. Stratus
cloud looks like a fog in the early morning and
evening when it remains close to earth's atmosphere. The weather becomes
calm when the sky is covered by stratus cloud. However, the thickening of
this cloud can cause snowfall, rainfall or drizzle.

4. Nimbus: Nimbus cloud is dark brown or grey
and thick, found at lower height that cause
heavy rainfall. These clouds remain at lower
level below 2000 m in the earth's atmosphere.
They have no fixed shape i.e. their shapes keep
on changing continuously. The lower part
of these clouds contains more water vapour.
They are responsible for continuous rainfall or
snowfall. Usually the nimbus clouds become thicker and dark to cover the
whole sky, then a heavy rainfall occurs along with thunderstorm, lightning,
snowfall and hailstones.

Science, Health and Physical Education Book - 5 117

Points to Remember

1. Weather is the condition of the atmosphere in a particular time at a
place.

2. The science that deals with the study of weather is called meteorology.
The person who studies weather is called a meteorologist.

3. Climate is the average or overall condition of weather at certain place
for a longer period of time.

4. Rainfall, clouds, wind, humidity, temperature, etc bring changes in
weather.

5. The sun is the main factor that causes the weather to change.
6. A monsoon is a seasonal wind which last for several months.
7. The cyclic change of water into water vapour, water vapour into cloud

and the cloud into rain is called water cycle.
8. Humidity is the amount of water vapour present in the air.
9. Weather forecasting is the process of predicting the weather of a

particular region.
10. Weather is forecasted after studying various factors of weather and

their condition through different media.
11. Clouds are formed by the condensation of water vapour of atmosphere

at high altitude.
12. Cirrus, cumulus, stratus and nimbus are four types of clouds.

Exercise

1. Choose the best answer from the given alternatives.

a. The day-to-day condition of the air around us is _________ .

i. climate ii. weather iii. humidity iv. rain

b. Clothes do not dry easily during _________ .

i. summer ii. monsoon iii. storm iv. cloudy

c. ______ of a place depends upon its distance from the Earth's equator.

i. weather ii. climate iii. water cycle iv. clouds

118 Science, Health and Physical Education Book - 5

d. A wind vane measures the __________ of wind.

i. speed ii. velocity iii. direction iv. destruction

e. Precipitation is recorded using a __________.

i. rain gauge ii. barometer iii. amemometer iv. hygrometer

f. _________ clouds are responsible for foggy conditions.

i. stratus ii. cirrus iii. cumulus iv. nimbus

2. Fill in the blanks with appropriate words.

a. The study of change in weather and its forecasting is ________.
b. The surface near the _________ of the earth is hot.

c. The _________ is the most important factor that brings changes in
weather.

d. The _________ is the process in which water circulates from the land
to the sky and back again.

e. The air with less water vapour is called __________ .

f. Hygrometer measures the __________ of atmosphere.

g. There is a possibility of __________ if the sky is suddenly covered
with black clouds.

3. Write 'T' for true and 'F' for false statements.

a. Weather conditions vary from place-to-place and from time to time.
b. The climate of a place is affected by its altitude.

c. The sun does not play any role to change the weather.
d. Humidity is a term for the amount of water vapour in the air.
e. Cirrus cloud is formed at a very low altitude.
f. Nimbus clouds cause heavy rainfall for a long time.

g. Clouds appear in different colours, shapes, sizes and appearance.

4. Match the following

Column A Column B

Thermometer measure the atmospheric pressure

Rain guage measure speed of wind

Anemometer measure relative humidity

Barometer measure the temperature

Hygrometer measure rainfall

Science, Health and Physical Education Book - 5 119

5. Give one word for the following.
a. The condition of air at any particular place and time.
b. The instrument used to measure wind speed.
c. This depends on the distance of a place from the equator and the
amount of sunlight it receives.
d. Scientists who study changes in weather conditions.
e. Clouds at the upper part that look like a cauliflower.
f. Clouds that are found at a lowest height.

6. Answer the following questions:
a. How does weather change from day to day?
b. What are the major factors that affect the climate of a place?
c. How does the sun causes changes in weather?
d. At what angle is the axis of the Earth tilted?
e. Why is it very hot in the afternoon than the morning?
f. What type of climate do Terai and Mountain region of our country
have?
g. How does humidity affect us?
h. When does Nepal experience monsoon season? What do the farmers
do in this season?
i. What is meant by weather forecasting? Write any four ways of
weather forecasting.
j. Explain briefly how weather satellites help farmers.
k. Name and explain briefly about the instruments that are used to
predict the weather.
l. How are clouds formed? Define water cycle.
m. Why does rainfall occur from clouds?
n. Name four different types of clouds. Explain them briefly.

7. Differentiate between
a. Weather and climate
b. Moist air and Dry air
c. Stratus clouds and Nimbus clouds

8. Give reasons of the following.
a. The surface of the earth does not get sunlight regularly.

120 Science, Health and Physical Education Book - 5

b. Weather forecasting is very important for us.
c. Days are shorter in winter than in summer.
Think and discuss
If the earth stops moving, what would it be like after two months?
Project work

• Collect newspaper reports on weather conditions that led to uprooting of

trees, flooding or drought like situations.

• Find out which weather conditions are not suitable for flying to the Mount

Everest. Paste dipping from magazines in your scrap book to show how the
mountain peak looks on a normal day.

Teacher's note
Students can be asked to listen to weather forecasts broadcast on TV or on radio
and discuss about the weather in the class. They can take turns to perform this
activity.

Science, Health and Physical Education Book - 5 121

11Lesson Solar System

Specific After the completion of the lesson, students will be able to:
Objectives • define and describe solar system.
• explain the basic features of the sun and its members.
• name the planets of the solar system in the order of increasing

distance from the sun.
• write about the phases of the moon briefly.
• explain eclipse and their types.

Mind Opener

Answer the following questions:

• What does the word 'universe' mean?

• Is the earth suitated at the centre of the universe?

• Is there a fixed pattern of arrangement of the heavenly bodies?

• Why don't the various heavenly bodies bump into each other as they
move?

Match the following:

Mercury known as red planet

Venus brightest and hottest planet

Jupiter largest planet

Neptune farthest planet

Mars smallest planet

Earth living planet

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Introduction

The vast surrounding space and

everything in it, including stars,

planets, satellites, etc is called the

universe. The science which deals

with the study of the universe is

called astronomy. The scientist

who studies about the universe Telescope Astronomer

is called an astronomer. To learn

about the universe, instruments like telescope and space probes are used.

The universe is an unlimited region that contains everything in the whole
creation. We can imagine the vastness of the universe from the fact that the
planet earth that we live on, is only a tiny speck in this vast universe. There
exists very tiny particles to the largest structures in the universe. It consists of
galaxies, constellations, stars, planets, satellites, comets, asteroids and other
bodies. They are very far from each other so the distance between them is not
measured in metre or kilometre. Their distance is measured in light year and
astronomical unit.

Stars

When you look at the sky on a clear night you see
hundreds of stars. They look like tiny jewels which
light up the sky and form beautiful patterns in it.
They give out their own light and most of them seem
to be twinkling. If you observe them carefully over
several clear night, you will notice that though they
appear to move from east to west, their position with respect to other heavenly
bodies seems to remain fixed.

Stars are huge shining balls of gases. They release their own light. So, they are
known as luminous bodies. The sun is also a star. It gives us both heat and
light. It is the closest star from the earth.

Some of the stars are smaller than the sun while some are bigger than the
sun. Stars are in a variety of sizes and colours. Our sun is an average sized
yellowish star. Stars which are smaller than our sun are reddish and larger
stars are blue in colour. Sirius is the biggest star till known.

Science, Health and Physical Education Book - 5 123

The sun

The sun is a medium sized star closest to the earth.
It is about 150 million kilometres (15 ×1011m) away
from the earth, which is close as compared to the
distance of other stars from the earth. Light takes
about 8 minutes to travel from the sun to the earth.
The sun is therefore said to be at a distance of 8 light
minutes from the earth. The sunlight which you receive at a particular time is
actually started travelling eight minutes earlier from the sun.

As compared to some of the other stars, the sun is rather small. However,
compared to the earth, it is very large. It has a diameter of about 1,392, 000
km. This is more than 109 times the diameter of the earth. The sun gives heat
and light to the earth. The earth receives only a small part of the total energy
given out by the sun. It is the main and ultimate source of energy. It supports
green plants to prepare their food during photosynthesis. Sunlight regulates
the water cycle on the earth.

The solar system

The solar system consists of a

large family of heavenly objects

which revolve round the sun.

Its largest and most important

members are the planet. So far

only eight planets have been

discovered. The earth on which

we live is one of them. All the

planets move round the sun in

its own path called orbits. There are also other smaller objects which move

round the sun. These are asteroids (minor planets) and comets. The whole

group of planets, asteroids and comets which move around the sun is called

the solar system. Do you know?
All the heavenly bodies in the solar

system revolve round the sun. They are The astronomer Kepler (1571-

constantly in motion in their own orbits. 1630) showed that planets

At the same time, they spin or rotate on move round the sun in

their own axis and maintain a uniform elliptical (oval-shaped) orbits.

124 Science, Health and Physical Education Book - 5

distance in relation to each other. They do not fall into the spaces nor do they
bump into each other. This is possible because of the strong pull of the sun
which pulls all bodies towards itself. In addition, there is a force of attraction
between the planets which pulls them towards each other. You will learn more
about this force of attraction later but in this grade, you will learn about planets
shortly.

Planets

The bodies which revolve around the sun are called planets. They do not have
their own light. They become bright due to light of sun and other stars. The
eight planets, in order of increasing distance from the sun are Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

There are minor planets in between the Mars and Jupiter called asteroids, which
divide the planets into inner planets and outer planets. The inner planets are
Mercury, Venus, Earth and Mars. These four planets are closest to the sun. The
outer planet are Jupiter, Saturn, Uranus and Neptune.

In the solar system, Mercury is the nearest planet while Neptune is the farthest
from the sun. Mercury is the smallest planet whereas Jupiter is the biggest
one. Mars is known as the red planet as it appears red in the sky. The earth is
known as the living planet as it has suitable temperature, water and oxygen
essential for survival of plants and animals.

Difference between stars and planets

Stars Planets
1. Stars emit their own light.
1. Planets do no emit their own light
2. They twinkle at night. but they reflect the light of sun.
3. They are larger in size.
4. They are very hot. 2. They do not twinkle.
5. There are billions of stars.
3. They are compalatively small.

4. They are not very hot.

5. There are only eight planets in the
solar system.

Artificial satellites

Artificial satellites are man made satellites which continuously revolve the
earth or some other heavenly body in the universe. Such satellites mainly

Science, Health and Physical Education Book - 5 125

gather information about the bodies they revolve. Most of the artificial satellites
revolve around the earth.

The first artificial satellite, Sputnik-1, was launched by the Soviet Union in 1957.
Since then, the United States and about 40 other countries have developed,
launched and operated artificial satellites so far. Depending upon their uses,
artificial satellites are of six main types.

Space research satellites : These satellites gather information about the
universe for research purpose.
Weather satellites : These satellites help scientists to study weather patterns
and forecast the weather.
Communication satellites : These satellites receive and transmit radio signals
around the world. They also send signals for television programmes and
telephone cells.
Navigation satellites: Navigation satellites help aircrafts, ships, etc to
determine their location.
Earth observation satellite: Such satellites gather information about our planet
like the status of natural resources on the earth and other changes.
Military satellites: These satellites collect information for military purposes.

Moon

The moon is the heavenly body that moves around
the planet. Like the planets, the moon does not have
its own light, but reflects the sunlight. Our moon is a
natural satellite.

Saturn has sixty moons and Jupiter has sixty three
moons. Some planets have no moons at all. For
example, Mercury and Venus do not have any moon.
The eight planets, along with their satellites revolve round the sun and make
up the solar system.

Phases of the Moon

The moon looks different daily. Different shapes of the moon are called the
phases of the moon. But actually, the moon does not change its shape at all. We
see different shapes due to the change in the position of the earth.

When the moon lies between the sun and earth, the portion of the moon facing
the earth is in complete darkness. This phase of the moon is known as new

126 Science, Health and Physical Education Book - 5

moon. After three days, a thin illuminated surface of the moon is visible from
the earth.

This position is known as crescent moon.

On the 7th day after the new moon, the

moon looks like a luminous half - circle.

This position is called first quarter. On the

10th day after the new moon, more than

half, but less than full part of the moon is Fig. Phases of moon

lighted. This position is called gibbous. On the 14th day after the new moon,

the moon looks fully lighted. This position is called full moon. After this, the

phases of the moon reverse. The new moon and the full moon occur alternately

at a regular interval of about 15 days. The time period between one full moon

to another full moon or one new moon to another new moon is about one

month. i.e. 29.5 days. This time period is called lunar month or synodic month.

Lunar calendar is made on the basis of the phases of the moon.

Shadows

A shadow is a dark area which is formed due to blockage of light. The shadow
is always formed on the side of the object away from the source of light. An
opaque object gives a dark shadow, a translucent object gives a faint shadow
while the transparent object does not cast any shadow. The size of the shadow
changes as the direction of the light source changes. For example, we see a long
shadow of our body in the morning and evening when the sun is at horizon.
But during the day time, they are shorter and the shortest at mid day when
the sun is overhead. We never get a shadow when there is no source of light
of any sort.

Activity 1

Take a torch light, a ball and a screen. In a
dark room, arrange the ball and screen in
a straight line. Take a torch light as shown
in figure and switch it on. A dark patch
can be observed on the screen. The dark
patch is called a shadow. The shadows
have one faint and one dark part overlapping each other. The dark part of
the shadow receives no light at all called the umbra. The fainter part of the
shadow around the umbra due to partially cut off light is called penumbra.

Science, Health and Physical Education Book - 5 127

Eclipses

Shine a torch towards a wall. Now put your hands between the torch and the
wall. Can you see the shadow of the hand on the wall? In the same way eclipse
occur. Usually, eclipse occurs due to the following two reasons.

a. The revolution of the earth round the sun and the revolution of the moon
round the earth.

b. During their revolution, sometimes the sun, earth and the moon come to
lie on a same straight line so that the shadow of one body may fall on the
other body.

Solar eclipse

Sometimes the moon comes in
between the sun and the earth. It then
blocks the light of the sun and casts
a shadow on the earth. The people in
the shadow area can not see the sun
at all, or can see it only partially. We
call this a solar eclipse. It occurs only
in new moon. But it does not occur
in every new moon as they do not fall in straight line in every new moon.

If the sun is completely blocked off by the moon, it is
a total solar eclipse. If it is partially blocked off, it is
called a partial solar eclipse. The eclipse ends as the
moon continues in its orbit and moves away from the
sun. A solar eclipse does not last for more than seven
minutes.

Do you remember that on May 20th, 2012 there was a total solar eclipse seen
from some parts of the world. This is very rare phenomenon and is of great
scientific importance. Many scientists had gathered to study various aspects
of this solar eclipse. The diagram shows the movement of the moon in front of
the sun causing total solar eclipse.

128 Science, Health and Physical Education Book - 5

Solar eclipse should not be seen with naked eyes. Along with visible light
sun also produces ultra violet (UV) light which is harmful to our eye. When
the sun is bright we cannot look at it for a long time. But in an eclipse when
intensity of light is less one can stare at the sun for a long time. Therefore more
UV light enters the eye and can damage it. The eclipse should be seen through
UV filters or only its reflection.

Activity

Make your own eclipse.

You need a large and a small pastic ball, two pieces
of thick iron wire, a bead with a hole, plasticine
and a bulb.

1. Paint a map of the world on the large plastic
ball. Push one of the iron wires through the
ball. Slip the bead on to the foot of the wire,
and fix the bead to a table using plasticine.

2. Bend the other piece of wire as shown and push it through the small
ball. The small ball is your moon.

3. Put the other end of the wire in the hole in the bead.

4. Swith on the bulb and move the moon around the earth and see solar
eclipse formed.

Lunar eclipse

When the earth comes in between the sun
and the moon, the shadow of the earth
fall on the moon. Then we have a lunar
eclipse. If the shadow of the Earth covers
the moon completely, there is a total lunar
eclipse. When it covers the moon only
partially, we have a partial lunar eclipse.

Lunar eclipse occurs on a full moon day. However, it does not occur on every
full moon day. This is because the earth, the moon and the sun are not in a
straight line on all full moon days.

Science, Health and Physical Education Book - 5 129

Points to Remember

1. The surrounding space including the earth, planets, stars and other
heavenly bodies is called the universe.

2. The sun and its eight planets with their satellites is called solar system.
3. The heavenly bodies that emit their own light and shine continuously

are called stars.
4. The sun is the nearest star from the earth.
5. There are eight planets that revolve around the sun.
6. The planets receive heat and light from the sun.
7. Satellites are smaller heavenly bodies that revolve around larger

planets.
8. The moon is the only natural satellite of the earth.
9. The change in the shape of the moon when observed from the earth

are called phases of the moon.
10. The bright part of the moon gradually increases from the new moon to

the full moon.
11. A dark shadow that forms behind the opaque objects is called an

umbra. A light shadow that forms outside the umbra is penumbra.
12. When the sun, the moon and the earth are in a straight line, on some

positions the moon and the earth cast their shadow on each other. This
phenomenon is called eclipse.

Exercise

1. Choose the best answer from the given alternatives.

a. The subject that deals the study of universe is ________.

i. Biology ii. Physics iii. Meteorology iv. Astronomy

b. ________ is the biggest star till known

i. sun ii. Jupiter iii. Satellite iv. Sirius

c. The distance between the sun and the earth is ________.
i. 1.5 × 1011m ii. 1.5 × 1012m iii. 15×1011m iv. 15×1012 m

130 Science, Health and Physical Education Book - 5

d. The diameter of the earth is _________ times greater than the diameter
of the sun.

i. 100 ii. 104 iii. 109 iv. 5

e. Saturn has _________ moons.

i. 60 ii. 18 iii. 1 iv. 6

f. Lunar eclipse occurs when the earth comes between:

i. the moon and the sun ii. the moon and the star

iii. the moon and the satellite.

2. Fill in the blanks with appropriate words.

a. ________ is the vast space that contains heavenly bodies in it.

b. The distance between the sun and the earth is _______ light minute.

c. The largest planet of the solar system is ___________.

d. _________ is the planet where life exists.

e. _________ is known as red planet.

f. During solar eclipse, the shadow of _________ falls on ________ .

g. A _________ occurs in the full moon period.

3. Write 'T' for true and 'F' for false statements.

a. The sun is the nearest star from the earth.

b. Planets have their own light.

c. Mercury is called morning star.

d. The earth is the only planet is which living organisms can survive.

e. The moon is the brightest object in the night sky.

f. All planets have moons.

g. Solar eclipse occurs when the moon comes between the sun and the
earth in a straight line.

h. Eclipses do not occur every new moon and full moon.

4. Match the following

Universe smallest planet

The sun biggest planet

Mercury unlimited space

Jupiter brightest star

Mars minor planets

Asteroids red planet

Science, Health and Physical Education Book - 5 131

5. Answer the following questions.
a. What is the universe?
b. What are stars? When do they twinkle?
c. Describe briefly about the sun.
d. What is solar system? Name the planets of solar system according to
their position from the sun.
e. Planets do not have light of their own, yet they are visible to us from
the earth. Why?
f. Name the hottest and the coldest planet of the solar system.
g. Why is the earth a suitable planet for the existence of life?
h. What is meant by phases of the moon?
i. What is a solar eclipse? When does a total solar eclipse occur?
j. What is lunar eclipse ? When does a total lunar eclipse occur?

6. Give reasons of the following
a. The sun is a star.
b. Moon is a satellite.
c. Artificial satellites are useful to us.
d. Earth is a living planet.
e. Mars is known as the red planet.
f. We should not watch a solar eclipse with naked eyes.
g. Lunar ecplise does not occur on every full moon day.

7. Differentiate between
a. Stars and planets
b. Planet and moon
c. Umbra and penumbra
d. Cresent moon and new moon.
e. Partial eclipse and total eclipse
f. Solar eclipse and lunar eclipse.

8. Draw a labelled diagram of
a. Solar system
b. Different phases of the moon
c. The solar eclipse
d. The lunar eclipse.

132 Science, Health and Physical Education Book - 5

Think and discuss

1. Why are some night darker than the others?
2. Why do we see different shapes of the moon every night from the earth?
3. If the earth is not tilted on its axis what would have been different?
4. The countries of northern and southern hemisphere experience opposite seasons.

Why?

Project work

1. Find out stories about Neil Armstrong and Buzz Aldrin from the internet. Make
a case study report on your finding.

2. Observe the different shapes of the moon daily for a month. Draw the diagram
of the shapes of the moon from new moon to full moon in your scrap book
with date in it.

Science, Health and Physical Education Book - 5 133

12Lesson The Earth

Specific After the completion of the lesson, students will be able to:
Objectives • explain the internal structure of the earth with a labelled diagram.
• describe the process of continuous change on the earth surface.
• explain the measures of the conservation of soil.

Mind Opener

• Label the following:

• Discuss and give one word for each.
• The largest mass of water on the earth.
• The largest mass of on the earth.
• The rocks and soil part of the earth.
• The layer of air that surrounds the earth.

134 Science, Health and Physical Education Book - 5

Introduction

The planet in the solar system where life exists is the Earth. The earth is
different from all other planets in the solar system. It has water, air, and soil
that are essential for life. There is a layer of air around the earth, called the
atmosphere, which protects it from the harmful ultraviolet rays of the sun.

Water covers about 70% of the earth's surface in the form of oceans, seas,
lakes, rivers, etc. The colour of the earth appears blue due to the presence of
large amount of water on its surface. The remaining 30% of the earth's surface
consists of land masses. The surface of the earth has various features such as
oceans, rivers, mountains and valleys.

Similarly, some areas on the earth's surface are covered with thick forests and
grasslands, whereas some have deserts.

But do you know what the inside of the earth looks like?

Internal structure of the Earth

Earth is a big round ball, slightly
flattened at poles and bulged out at
equator. Its shape is somewhat like
that of an orange. Its outer part is hard
but the inner part has molten mass of
elements. The earth is made up of soil,
rocks and metals consisting of several
layers. Each layer has its own physical
properties and chemical composition.
The earth has three layers which are described below.

1. Crust

Crust is the outermost layer where we Info bits
live. About 70% of it is covered with
water (in the form of oceans, lakes, rivers The earth's crust is divided into
and snow) whereas the rest of it is in the several plates which can move.
form of land which forms the continents When these plates collide
of the earth. As the crust is made up of earthquakes are caused.
rocks and soil, it is solid and hard layer.

Science, Health and Physical Education Book - 5 135

It's thickness is about 5km to 50 km. The thickness of crust is less beneath the
oceans. The crust mainly consists of soil, rocks, minerals, water and air.

2. Mantle

The layer just below the crust is called mantle. The boundary between the crust
and the mantle is called moho. The thickness of this layer is about 2900 km.
The temperature of this layer lies between 750oC to 2500oC. The substances
present in this layer are in the semi liquid forms. The molten materials found
in this layer is called magma. It may come out during volcanic eruption. The
different minerals or elements found in this layer are iron, magnesium, silica
etc.

3. Core

The layer of the earth which lies below the mantle is called core. It is the thickest
layer of the earth. It consists of outer core and inner core layers. The thickness
of the outer core is about 2100 km. The materials found in this layer are in
molten state. This layer consists of iron, nickel and cobalt. The temperature of
this layer ranges from 2500oC - 4000oC. The inner core is the centre of the earth
having thickness of about 1300 km. The temperature of this layer is very high
but the materials found in this layer are in solid state due to excessive pressure
of the outer layers. It also consists of iron and nickel.

Activity 1

Make a model of the earth using clay and other objects showing the major
layers.

Continuous changes on the earth's surface.

You might have seen muddy water in the river in rainy season. How does
water become muddy? How might the dust be deposited on your terrace every
morning? Have you ever thought? There are various changes that occur in the
earth's surface. Rainfall, wind, heat of the sun, earthquake, etc are responsible
for those changes.

During rainy season, we have seen landslide and flood. During these processes,
the soil gets washed away along with them from its original position. Similarly,
the loose layer of the soil are carried by the blow of wind. These particles are
mixed with the air and deposited in another place. Thus, erosion is the wearing
away of the land surface by the agents such as moving water, wind, etc.

136 Science, Health and Physical Education Book - 5

The eroded materials such as soil, sand and fragments are carried away by
different agents and are deposited somewhere else. This process is called
deposition. Erosion and deposition go side by side.

Soil erosion, deposition, flood, landslide, earthquake are frequently occuring
on the earth's surfaces. These disasters cause change on the earth's surface.
Earth's surface was not as it is at present and will not remain in future as it
is in present. There used to be ocean where there is plains today. The valleys
have been raised to mountains and mountains fell to plateau or valleys over
millions of years. Even these days, the high hills, mountains are being eroded
and valleys are rising due to soil erosion and deposition continuously. But
we cannot notice it as it is a slow process. In such ways, there is continuous
change on the earth's surface.

Factors that cause change on the surface of the earth

The following factors are responsible for changes on the surface of the earth.

1. Heat of the sun
2. Wind and storm
3. Rainfall
4. Deforestation and overgrazing
5. Earthquake and volcano
6. Unscientific agricultural practices.

1. Heat of the sun

Rocks during the day get heated and expand by
solar heat while during the night they lose heat and
contract. When this process continues for a long time,
cracks develop on the rocks and become weak. As a
result, big rocks break into smaller rocks and finally
into soil. Also solar heat changes snow into water and
water in the sea level rise, which brings out changes
on the surface of the earth.

Activity 2

Take a kettle and boil some water in it. At the same time take a trough full
of cold water. Bring a glass tumbler and fill it half with boiling water, now
keep it carefully in the cold water of the trough. Observe, what happen?

Science, Health and Physical Education Book - 5 137

2. Wind and storm

Fast moving air is called a wind and violently moving
air is called a storm. When wind and storm blow,
they take soil particles away from its original place
and help in the formation of dunes which brings out
changes on the surface of the earth.

3. Rainfall

Heavy rainfall causes different changes on the earth's
surface. Rainfall causes landslide in the slopes and
hills. It carries soil, sand and rock fragments along
with other materials deposit on other places. Slowly
rain erodes rocks as well. Similarly, rain water often
gets trapped in small cracks and crevices in rocks. In
cold regions, this water freezes and expands slightly.
This expansion produces a sideways pressure which
causes the cracks and crevices to become wider. As more and more water gets
trapped in these widened cracks, they expand further on freezing and force
the rocks to break.

Activity 3

Wrap a glass bottle full of water in a thick sheet of paper and leave this in
an ice box or refrigerator for a few hours. After some time you will notice
that the bottle cracks.

This happens because water expands on freezing and takes up more space.
It pushes against the walls of the bottle and forces it to crack.

4. Deforestation and Overgrazing

People clear forests for settlement
and getting land for farming. This
process is called deforestation.
Due to population growth, a
large number of trees are cut
down day-by-day for cultivation,
wood, timbers as well as to fulfill

138 Science, Health and Physical Education Book - 5

other demands. Overgrazing means leaving many cattles to graze freely in
grasslands and forests. These both factors, i.e., deforestation and overgrazing
destroy forests and grass lands. Ultimately, it makes the land weaker and the
soil loose. The loose soil from the weaker surface of the earth is eroded by
many agents like rain, river, winds, etc. Thus, deforestation and overgrazing
play a significant role to cause soil erosion, landslide, flood, etc. on the earth's
surface causing destruction that changes the earth's surface.

5. Earthquake and Volcano

The sudden violent shaking of
the earth's surface is called an
earthquake. The earthquake
causes landslides and sometimes
floods too. Even earthquake
shakes the high hills, mountains
and brings them down to the
ground or form pleatue. Similarly, during earthquake low land may rise to
form hills and pleatues. Besides, it causes the destruction of buildings, roads,
dams, bridges, etc. Similarly, volcanic eruption causes earthquake as well as
forms craters and mountains on the earth's surface. Thus, we can say that
earthquake and volcano bring changes on the surface of the earth.

6. Unscientific agricultural practices

In the hilly regions, unscientific agricultural practices
cause landslides and soil erosion. Generally, farmers
cultivate crops without making terraces in hilly
regions which makes the soil loose. Such loose soil
is easily carried away by rain water and wind from
the land and hills. Thus, terrace farming should be
adopted to grow crops on the slope of a hill by making
steps on the slope of a hill. This slows the flow of rain water and prevents soil
erosion.

Science, Health and Physical Education Book - 5 139

Points to Remember

1. The earth is a living planet.
2. The earth is flattened at the poles and bulged out at the equator.
3. The surface of the earth is composed of about 30% of land and the

remaining 70% of water.
4. The three major layers of the earth are: crust, mantle and core.
5. Crust is the outer most layer of the earth.
6. The mantle is made up of semi molten rock.
7. The outer core is a liquid layer made up of iron and nickel.
8. The inner core is the hottest part of the earth with extremely high

temperature.
9. The process in which the top layers of the soil is moved away from its

original place is called soil erosion.
10. The eroded particles get collected in a place, that is called deposition.
11. Heat of the sun, wind, storms, rainfall, deforestation, earthquake, etc

are some of the factors that bring changes on the earth's surface.

Exercise

1. Choose the best answer from the given alternatives.

a. The earth's surface consists of ________.

i. rivers ii. mountains iii. pleatue iv. all of them

b. About 70 percent of the earth surface is covered with ________.

i. land ii. valley iii. mountains iv. water

c. The middle layer of the earth is ________.

i. crust iii. core iii. mantle iv. atmosphere

d. ________ is the process of breaking down of rocks into soil particles.

i. erosion ii. deposition

iii. weathering iv. transportation

140 Science, Health and Physical Education Book - 5

e. Soil erosion and _________ bring change on the earth's surface,

i. blowing ii. deposition iii. rocks iv. terrace

f. Magma is found in ________.

i. mantle ii. core iii. crust iv. mountain

2. Fill in the blanks with appropriate words.

a. The earth is flat at _________ and bulged out at _________ .

b. Internal structure of the earth is divided into __________.

c. The thickness of the crust is _________.

d. The mantle consists of dense rock in _________ state.

e. ________ is the process of accumulation of earthy materials in a place.

f. The sudden violent shaking of the earth is called _________ .

g. The hot molten materials of mantle is called __________ .

h. The washing away of top fertile soil is called _________.

3. Write 'T' for true and 'F' for false statements.

a. The earth is made up of soil, rock and water.

b. Land covers almost 70% of the earth's surface.

c. Mantle is the thickest layer of the earth.

d. The materials found in inner core are in liquid state.

e. Erosion and deposition go side by side.

f. River is responsible for the erosion and deposition of soil.

g. Heat, cold, the wind and water are the agents that change the surface
of the earth.

i. Terrace farming increases the possibility of soil erosion.

4. Match the following

Atmosphere materials are in molten state

Crust materials are in solid state because of pressure

Mantle wearing of rocks and soil

Outer core outermost layer of the earth

Inner core layer of air that surround earth

Erosion second layer of the earth

Landslide control the soil erosion

Terrace farming major agent of change

Science, Health and Physical Education Book - 5 141

5. Define the following terms

a. crust b. wind and storm c. Earthquake

6. Answer the following questions.

a. What is the shape of the earth?

b. What are the layers of internal structure of the earth? Mention their
main features.

c. How is the crust important for living things?

d. Why is the inner core in solid state though it is very hot?

e. Write two differences between mantle and core.

f. List any four factors that bring changes on the earth's surface.

g. How does heat of the sun bring changes on the earth's surface?

h. Describe in brief the role of rainfall and overgrazing to bring change
in earth' surface.

i. Draw a diagram showing different layers of the earth.

7. Differentiate between

a. Crust and mantle

b. Soil erosion and soil deposition.

8. Give reasons of the following.

a. Life is possible only on the earth.

b. The surface of the earth is changing continuously.

c. Volcano and earthquake bring changes on the earth's surface.

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