CBSE Class 5 Social Science Rotation and Revolution of the Earth Notes Set 02

Words to know

1. Axis: an imaginary line passing through the Earth from the North Pole to the South Pole, around which the Earth spins. 2. Equator: an imaginary line drawn around the middle of the Earth, at equal distance from the North Pole and the South Pole. 3. Orbit: the fixed path along which the Earth moves around the Sun. 4. Revolve: to move in a circle around a central point.

Rotation of the Earth

The Earth spins on its axis like a top. This spinning movement is called rotation. One full rotation takes about 24 hours, which is one day. The Earth rotates from west to east, so the Sun appears to rise in the east and set in the west.

Day and night

The Earth is round, so the Sun can light up only half of it at a time. The half facing the Sun has day. The other half, turned away from the Sun, is dark and has night. As the Earth rotates, every place moves from the lit half to the dark half and back again, so we get day and night one after the other. Rotation is therefore the cause of day and night.

Revolution of the Earth

Besides spinning, the Earth also travels around the Sun along its orbit. This movement is called revolution. One complete revolution takes about 365 days, or one year. Actually it takes about 365 and a quarter days. The extra quarter days add up to one day every four years, so we add a day, 29 February, to make a leap year of 366 days.

Rotation and revolution compared

1. Rotation is the spin of the Earth on its axis; revolution is its movement around the Sun. 2. Rotation takes about 24 hours; revolution takes about 365 days. 3. Rotation causes day and night; revolution, together with the tilt of the axis, brings about the change of seasons.

Why we do not feel the movement

The Earth is huge, and everything on it, including air, water and us, moves along with it at a steady speed. Because the movement is smooth and everything moves together, we cannot feel it, just as passengers in a smoothly moving train do not feel the speed. We know about rotation from its effects: the Sun, Moon and stars seem to move across the sky, and day turns into night.

Seasons in brief

The Earth's axis is not straight up. It is tilted. As the Earth revolves around the Sun, different parts of the Earth lean towards the Sun at different times of the year. The part leaning towards the Sun receives more heat and has summer, while the part leaning away has winter. This is why the weather in a place changes through the year.

Worked examples

Example 1. How many times does the Earth rotate in a week? Answer: Once a day, so it rotates 7 times in a week.

Example 2. When it is day in India, what is it in the part of the Earth facing away from the Sun? Answer: It is night there, because that half receives no sunlight.

Example 3. How many days are there in three ordinary years? Answer: 3 × 365 = 1095 days.

Quick Check Questions