krit.club logo

Earth, Moon, and the Sun - Rotation of the Earth

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

The Earth rotates on its own axis from West to East. This movement is called rotation.

•

The axis of the Earth is an imaginary line that is tilted at an angle of 23.5∘23.5^\circ to the vertical, or 66.5∘66.5^\circ to its orbital plane.

•

The Earth takes approximately 2424 hours to complete one rotation around its axis, which is known as a solar day.

•

Rotation causes the phenomenon of day and night. The part of the Earth facing the Sun experiences day, while the part facing away experiences night.

•

The imaginary line that separates the day from the night on the globe is called the Circle of Illumination.

•

The speed of Earth's rotation is highest at the Equator (approximately 1,670 km/h1,670 \text{ km/h}) and decreases towards the poles where it is zero.

📐Formulae

Time for 1 Rotation≈24 hours\text{Time for } 1 \text{ Rotation} \approx 24 \text{ hours}

Angular Velocity=360∘24 hours=15∘ per hour\text{Angular Velocity} = \frac{360^\circ}{24 \text{ hours}} = 15^\circ \text{ per hour}

Time taken for 1∘ rotation=60 minutes15=4 minutes\text{Time taken for } 1^\circ \text{ rotation} = \frac{60 \text{ minutes}}{15} = 4 \text{ minutes}

Speed at Equator(v)=2πrT\text{Speed at Equator} (v) = \frac{2 \pi r}{T}

💡Examples

Problem 1:

If the Earth rotates 360∘360^\circ in 2424 hours, calculate the time taken to rotate through 15∘15^\circ.

Solution:

Time=24 hours360∘×15∘=1 hour\text{Time} = \frac{24 \text{ hours}}{360^\circ} \times 15^\circ = 1 \text{ hour}

Explanation:

Since a full rotation of 360∘360^\circ takes 2424 hours, we divide the total time by the total degrees and multiply by the required degrees to find the time for 15∘15^\circ.

Problem 2:

Calculate the difference in time between two longitudinal points that are 30∘30^\circ apart.

Solution:

30 degrees×4 minutes/degree120 minutes\begin{array}{r} 30 \text{ degrees} \\ \times 4 \text{ minutes/degree} \\ \hline 120 \text{ minutes} \end{array} 120 minutes=2 hours120 \text{ minutes} = 2 \text{ hours}

Explanation:

Every 1∘1^\circ of longitude corresponds to a 44-minute time difference. Therefore, 30∘30^\circ corresponds to 30×4=12030 \times 4 = 120 minutes, which is 22 hours.

Problem 3:

Determine the angle of Earth's tilt relative to its orbital plane if its tilt from the perpendicular is 23.5∘23.5^\circ.

Solution:

90.0−23.566.5\begin{array}{r} 90.0 \\ - 23.5 \\ \hline 66.5 \end{array} The angle is 66.5∘66.5^\circ.

Explanation:

The axis is tilted 23.5∘23.5^\circ from the line perpendicular to the orbital plane. To find the angle with the orbital plane itself, we subtract the tilt from a right angle (90∘90^\circ).