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Class VI - social: Motions of Earth
One Word Answer Questions:
Q) What are the two motions of the Earth?
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Q) Which direction does the Earth spin?
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Q) How long does Earth take to complete rotation?
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Q) What is the shape of the Earth?
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Short Answer Questions:
Q) What is dawn?
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Q) What is dusk?
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Q) What are the effects of Earth's rotation?
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Q) Explain rotation of the Earth?
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Q) What is leap year? Explain?
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Q) What is Equinoxes ? Write few important points related to Equinox?
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Long Answer Questions:
Q) Explain in detail the process of day & night ?
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Q) Explain the revolution of the Earth?
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Q) How does season change? Explain in detail?
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Motions of the Earth

    All the objects in space move - the Sun, the Stars, the Planets and other heavenly objects. The Earth is also constantly moving. The two motions of the Earth are rotation and revolution. The Earth rotates on its axis and revolves around the Sun.

Rotation of the Earth
  • The Earth spins on its axis from west to east.
  • This spinning of the Earth around its own axis is known as rotation.
  • The Earth takes about 24 hours to complete one rotation.
  • The speed of rotation at any point along the equator is approximately 1671 km per hour.
Motions of the Earth
Rotation of the Earth

Effects of the Earth's Rotation

    The rotation of the Earth causes:

  • Day and night
  • Bulging of the Earth at the equator, and flattening at the poles
  • The deflection of winds and ocean currents
  • The alternate rise and fall of the oceans due to gravity of the Moon and the Sun, and the rotation of the Earth
  • The apparent movement of all the heavenly bodies from the east to the west
Motions of the Earth
Day and Night
Motions of the Earth
Rotation of Earth
Day and Night
  • Day and night are caused by the rotation of the Earth.
  • The Earth rotates from west to east and the Sun appears to rise in the east.
  • Only one side of the Earth can face the Sun at any time because Earth is spherical in shape.
  • The side that faces the Sun experiences day and the side that is turned away from the Sun experiences night.
  • The line that separates the lighted half from the darker half of the Earth is called the circle of illumination.
  • In the course of 24 hours, places on Earth experience each of these stages one after the other - dawn, sunrise, mid-day, sunset, dusk and mid-night and then dawn again.
  • Dawn is that time of a day just before sunrise. Dusk is that time of a day just after sunsets in the west.
Motions of the Earth
Circle of Illumination

Revolution of the Earth
Revolution
  • The movement of the Earth around the Sun is called revolution.
  • The Earth takes 365 days or one year to complete a revolution.
  • The path it takes around the Sun is known as the orbit.
  • The Earth's orbit is elliptical (shaped like an egg).
  • The distance between the Earth and the Sun varies from a minimum of roughly 147 million km in early January, called the perihelion and to a maximum of roughly 152 million km in early July, called the aphelion.
  • The plane in which the Earth goes around the sun is called the ecliptic.
Motions of the Earth
Revolution of the Earth

Effects of the Earth Revolution

    The revolution of the Earth, along with the tilt in the Earth's axis, causes:

  • Verifying length of day and night
  • Changing season
    If the Earth's axis were straight and not tilted, there would be no season. Every point on the Earth would receive the same amount of light each day of the year.
Varying lengths of day and night
  • Half of the year, the Northern Hemisphere faces the Sun, while for the next six months; the Southern Hemisphere faces the Sun.
  • A large part of the hemisphere that faces the Sun gets sunlight. This means that the hemisphere facing the Sun gets longer days and shorter nights.
  • At the equator the days and nights are of equal length.
The Changing Season
  • The axis of the Earth is inclined at an angle of 23 ½ ° to its perpendicular plane. When this tilt in the axis is combined with the revolution of the Earth, we get the changing season.
  • The Northern Hemisphere is inclined towards the Sun and the Southern Hemisphere is turned away from the Sun between the 21 March and 23 September.
  • Since the North Pole is inclined towards the Sun during this period, the Northern Hemisphere has longer days and shorter nights.
  • This part of the Earth also gets heated more. It is summer here.
  • During this period the Southern Hemisphere faces away from the Sun and gets slanting rays of the Sun.
  • Southern Hemisphere has longer nights and shorter days,it is winter there.
  • On 21 June the Sun's rays falls vertically on the Tropic of Cancer. In the Northern Hemisphere it is the longest day of the year. It is called summer solstice.
  • On 22 December the sun's rays falls vertically on the Tropic of Capricorn. It is the longest day of the year in the Southern Hemisphere.
  • In the Northern Hemisphere it is the shortest day of the year. It is called the winter solstice.
Motions of the Earth
The changing season

Equinoxes
  • On 21 of March and 23 September every year the Sun's rays fall vertically on the equator. These days are known as the equinoxes
  • The North Pole and South Pole are neither inclined towards the Sun; nor are they inclined away from it.
  • On these days maximum heat and light is received at the equator.
  • Both hemispheres receive the sunrays equally. Therefore, the length of day and night is equal all over the world.
  • March 21 is known as the vernal or spring equinox and September 23 is known as the autumnal equinox.
The Four Seasons
  • The different positions of the Earth during its revolution around the Sun are thus responsible for the seasons.
  • Thus in the Northern Hemisphere, the seasons follow the pattern of spring beginning in March, summer in June, autumn in September, and winter in December.
  • In the Southern Hemisphere the pattern is reversed, with autumn beginning in March, winter in June, spring in Septemberand summer in December.
Motions of the Earth
The changing season

Leap Years
  • The Earth takes 365 ¼ days to complete one revolution around the Sun.
  • 365 days consider as a calendar year and the 6 hours which left every year is added in the month of February once in every four years.
  • Every fourth year has 366 days and it is called a leap year.
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