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Question A.1:

The speed of the earth's rotation at the equator is about

a. 1,675 m per second
b. 1,675 km per hour
c. 1,675 miles per hour
d. 1,675 km per minute

The correct answer is option (b).

Explanation: The Earth’s rotational speed at the Equator is 1,675 km/h. The Earth's rotational speed is maximum at the Equator; it reduces as we move towards the poles.

Question A.2:

The time of the day just before sunrise is known as

a. dusk
b. twilight
c. dawn
d. morning

The correct answer is option (c).

Explanation: During the dawn, the Sun remains below the horizon, so the Earth receives very less sunlight.

Question A.3:

Which of the following places enjoy day and night throughout the year?

a. Antarctic Circle
b. Tropic of Cancer
c. Equator
d. Tropic of Capricorn

The correct answer is option (c).

Explanation: The Equator receives direct rays of the Sun throughout the year, so the length of the day and that of the night experienced at the Equator never change.

Question A.4:

In which of the following years, February has 29 days?

a. 2000
b. 2010
c. 2014
d. 2006

The correct answer is option (a).

Explanation: A leap year is evenly divisible by 4 and 400.

Question A.5:

Which one of the following factors is not responsible for the phenomenon of seasons?

a. Rotation of earth
b. Revolution of earth
c. Earth's inclination
d. Gravitational pull on sun

The correct answer is option (d).

Explanation: The factors given in options (a), (b) and (c) have serious effects on seasons. However, the factor given in option (d), i.e. the gravitational pull of the Sun, does not affect seasons.

Question A.6:

The longest day in the Southern Hemisphere is on

a. 22 March
b. 22 September
c. 21 June
d. 22 December

The correct answer is option (d).

Explanation: On 22 December, the day of winter solstice, the Southern Hemisphere experiences the longest day.

Question A.7:

Christmas is celebrated during the summer season in

b. Italy
c. New Zealand
d. Switzerland

The correct answer is option (c).

Explanation: It is summer in New Zealand on 25 December, i.e. Christmas. This is because New Zealand is situated in the Southern Hemisphere, where the season is just the opposite of the season experienced at the same time in the Northern Hemisphere.

Question A.8:

On which of the following days is the sun overhead at the equator during noon?

a. 22 December
b. 21 March
c. 21 June
d. 4 January

The correct answer is option (b).

Explanation: Spring equinox occurs on March 21. So, the Sun is overhead at the Equator, due to which both the hemispheres experience equal length of day and night.

Question B:

1. The earth rotates on its axis from ___________ to ____________
2. The axis of the earth is inclined at an angle of ___________
3. The variation in the length of days and nights is due to _____________ on the earth's axis.
4. The earth's orbit around the sun is __________ in shape.

1. The correct answer is  west to east.

Explanation: West to east is the direction in which the Earth rotates on its axis.

2. The correct answer is  66.5 degrees.

Explanation: The axis of the Earth is not a straight line. It is inclined at an angle of 66.5 degrees. This causes varying lengths of day and night in both the hemispheres.

3) The correct answer is  inclination

Explanation: The Earth's axis is inclined at an angle of 66.5 degrees. This causes varying lengths of day and night in both the hemispheres.

4)The correct answer is  elliptical .

Explanation: Due to the elliptical shape of the orbit, the Earth does not remain equidistant from the Sun throughout the year. There arises situations of aphelion and perihelion.

Question C:

1. The axis of the earth is always inclined in the same direction. ________
2. The diffuse light after sunset is known as dusk. __________
3. When the distance between the earth and the sun is minimum, the earth is in aphelion. _______
4. The Tropic of Cancer experiences the longest day on 21 June every year. ___________

1. The given statement is true.

Explanation: The Earth is always inclined in the same direction, i.e. towards the Pole Star.

2. The given statement is false.

Explanation: The diffused light after sunset is known as twilight.

3. The given statement is false.

Explanation: When the distance between the Earth and the Sun is minimum, it is called perihelion.

4. The given statement is true.

Explanation:
June 21 is the longest day in the Northern Hemisphere.

Question D:

 Column A Column B 1. Summer solstice in the Northern Hemisphere a. 21 March 2. Winter solstice in the Northern Hemisphere b. 21 June 3. Spring equinox in the Northern Hemisphere c. 23 September 4. Autumnal equinox in the Northern Hemisphere d. 22 December

 Column A Column B 1. Summer solstice in the Northern Hemisphere a. 21 June 2. Winter solstice in the Northern Hemisphere b. 22 December 3. Spring equinox in the Northern Hemisphere c. 21 March 4. Autumn equinox in the Northern Hemisphere d. 23 September

Question E:

Distinguish between the following.

1. Rotation and revolution
2. Dawn and twilight
3. Perihelion and aphelion
4. Solstice and equinox

 Rotation Revolution It refers to the movement of the Earth about its own axis. It refers to the movement of the Earth around the Sun. This motion causes day and night. This movement is the reason behind the occurrence of different seasons

 Dawn Twilight The diffused light during sunrise is known as dawn. The diffused light after sunset is known as twilight.

 Aphelion Perihelion When the distance between the Earth and the Sun is maximum, it is called aphelion. When the distance between the Earth and the Sun is minimum, it is called perihelion. It is 151 million kilometres. It is 146 million kilometres.

 Solstice Equinox It is the position of the Earth during summer and winter. It is the position of the Earth during spring and autumn. It is of two types: summer solstice and winter solstice. It is of two types: spring equinox and autumn equinox.

Question F:

1. the earth stops rotating and revolving?
2. the earth stars rotating at a slower speed?
3. the earth stars rotating at a faster speed?
4. the earth's axis becomes vertical?

1. If the Earth stops rotating and revolving, there will be no change of seasons and no day and night.
2. If the Earth starts rotating faster, the length of a day would be less than 24 hours.
3. If the Earth starts rotating slower, the length of a day would be more than 24 hours.
4. If the Earth’s axis becomes vertical, the length of the day and that of the night would be equal at all places throughout the year.

Question G.1:

What is the daily motion of the earth called?

The daily motion of the Earth is called rotation.

Question G.2:

What is the cause of the bulging of the earth at the equator?

The bulging of the Earth at the Equator is due to the rotation of the Earth on its own axis.

Question G.3:

What is the cause of day and night?

Day and night are caused by the rotation of the Earth around its own axis.

Question G.4:

What is the speed of the earth's rotation at the North Pole?

The rotational speed of the Earth at the North Pole is zero.

Question G.5:

What is the length of daylight at the equator?

The length of daylight at the Equator is 12 hours.

Question G.6:

What is the annual motion of the earth called?

The annual motion of the Earth is called revolution.

Question G.7:

How many days are there in a leap year?

There are 366 days in a leap year.

Question G.8:

When is New Year Day celebrated according to the India National Calendar?

According to the Indian national calendar, New Year's Day is celebrated on the first day after the spring equinox, i.e. on 21 March.

Question H.1:

What is the importance of the inclination of the earth's axis?

Due to the inclination of the Earth’s axis, the lengths of day and night are not the same throughout the year at different places on the globe. Due to this inclination, the Northern Hemisphere remains inclined towards the Sun for half of the year and the Southern Hemisphere remains so for the other half of the year.

Question H.2:

Why are days longer than nights during the summer season?

During summer, in the Northern Hemisphere, the North Pole is inclined towards the Sun, due to which a large portion of the Northern Hemisphere receives more heat and light. That is why days are longer than nights in summers.

Question H.3:

Why do we have a leap year?

The Earth takes 365 days and 6 hours to complete one revolution around the Sun. However, for our convenience, we count only 365 days in a year and the balance of extra 6 hours is added every year for four years and is computed as one extra day after those four years. This year having 366 days is known as a leap year.

Question H.4:

What are the factors responsible for the change of seasons?

The factors responsible for the change of seasons are as follows:

1. Rotation of the Earth around its axis
2. Revolution of the Earth around the Sun
3. Inclination of the Earth’s axis

Question I.1:

What are the effects of the earth's rotation?

Following are some of the effects of Earth’s rotation:

1. It causes the bulging of the Earth at the Equator.
2. It causes days and nights.
3. It causes tides twice a day.

Question I.2:

How are days and nights caused?

Days and nights are caused by the rotation of the Earth around its own axis. Due to the spherical shape of the Earth, only one half of the Earth gets light and heat from the Sun at a particular time. The portion of the Earth that receives sunlight is known as day, while the other portion is known as night.

Question I.3:

Explain the phenomenon of season with the help of a diagram.

Following are the factors responsible for the change of seasons:
Rotation of the Earth around its axis
Revolution of the Earth around the Sun
Inclination of the Earth’s axis

The Earth moves in an elliptical orbit and completes one revolution in 365 1/4 days. The axis of the Earth is tilted along the orbital plane and this tilt causes seasons. Because of this reason, different parts of the Earth receive different amounts of sunlight at different times of the year and hence experience change in seasons. When the axis faces the Sun, the respective hemisphere experiences summer. When the axis faces away from the Sun, the respective hemisphere experiences winter.

The above diagram shows how seasons are caused.

Question I.4:

What are the effects of the earth's revolution?

The movement of the Earth around the Sun is known as revolution. Revolution has the following effects:

1. It causes variation in the lengths of day and night.
2. It causes variation in the distribution of heat over the surface of the Earth.
3. It is responsible for the phenomenon of seasons.

Question I.5:

Why are days and nights not of equal duration throughout the world?

The lengths of days and nights are not the same throughout the year. This variation is because of the inclination of the Earth’s axis. The axis of the Earth is an imaginary line that passes through its centre. This axis is not vertical but is inclined at an angle of 66.5 degrees with the plane of the Earth’s orbit. Due to this inclination, the Northern Hemisphere remains inclined towards the Sun for half of the year and the Southern Hemisphere during the other half. Had the axis of the Earth been vertical, the lengths of days and nights would have been the same throughout the year all over the world.

Question I.6:

Why are the days and nights of equal duration throughout the world on equinoxes?

During the spring and autumn equinoxes, i.e. on 21 March and 23 September, the Sun is exactly overhead the Equator and the North and South Poles lie at an equal distance from the Sun. This is the reason days and nights are of equal length throughout the world on these two days.

Question I.7:

Why are the sun's rays never vertical on the Arctic Circle?

The axis of the Earth is an imaginary line that passes through its centre. This axis is not vertical but is inclined at an angle of 66 .5 degrees with the plane of the Earth’s orbit. Due to this inclination, the Northern Hemisphere remains inclined towards the Sun for half of the year and the Southern Hemisphere remains inclined during the other half. On summer solstice, in the Northern Hemisphere, the midday Sun is vertically overhead the Tropic of Cancer. This is the northernmost latitude till which the midday Sun can reach vertically overhead. Farther north than this, the Sun is never vertically overhead, and that is why the Arctic Circle never experiences the vertically overhead Sun.

Question I.8:

Why is the revolution of the earth around the sun also called the annual motion of the earth?