# Rotation And Revolution

## What is Rotation and Revolution?

A rotation is a circular movement of an object around a center of rotation. If a three-dimensional object like earth, moon and other planets always rotates around an imaginary line called a rotation axis. The axis passes through the body’s center of mass, the body is said to rotate upon itself or spin.

While, revolution is often used as a synonym for rotation. But in many fields like astronomy and its related subjects, the revolution is referred as orbital revolution. It is used when one body moves around another while rotation is used to mean the movement around the axis. For example: Moon revolve around the Earth, and the Earth revolve around the Sun.

### Rotation and Revolution of Earth

#### Rotation of the Earth

The spinning of the Earth around its axis is called ‘rotation’. The axis has an angle of $23 \frac{1}{2}^{\circ }$ and is perpendicular to the plane of Earth’s orbit. Which means, Earth is tilted on its axis, and because of this tilt, the northern and southern hemispheres lean towards away from the Sun. The rotation of the Earth divides it into a light up half and a dark half, which gives rise to day and night.

#### Revolution of the Earth

The movement of the Earth around the Sun in a fixed path is called revolution. The Earth revolve from west to east i.e, in the anticlockwise direction. The Earth completes one revolution around the Sun in one year or precisely in 365.242 days.

### Rotation and Revolution of Planets

 Planets Mean distance from the Sun in millions of kilometers Period of Revolution Period of Rotation Mercury 57.9 88 days 59 days Venus 108.2 224.7 days 243 days Earth 149.6 365.2 days 23 hr, 56 min, 4 sec Mars 227.9 687 days 24 hr, 37 min Jupiter 778.3 11.86 years 9 hr, 55 min, 30 sec Saturn 1,427 29.46 years 10 hr, 40 min, 24 sec Uranus 2,870 84 years 16.8 hours Neptune 4,497 165 years 16 hr, 11 min

### Difference Between Rotation and Revolution

The table given below provides the basic differences between the rotation and revolution.

 Rotation Revolution Rotation of the Earth is its turning on its axis. Revolution is the movement of the Earth around the Sun. The Earth takes 24 hours to complete a rotation around the Sun. The Earth takes a full year (365 days) for one complete revolution around the Sun The Earth’s axis of rotation is tilted by 23.5 degrees. This tilt causes the different seasons of the year. The path of the Earth moving around the Sun is called an orbit. The Earth’s orbit is elliptical.

#### Practise This Question

Two blocks of masses m1 and m2 are joined by a wire of Young’s modulus Y via a massless pulley. The area of cross-section of the wire is S and its length is L. When the system is released, increase in length of the wire is