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Why does the Earth assume the shape of an oblate ellipsoid?
Explanation
The Earth is not a perfect sphere but an oblate ellipsoid (or oblate spheroid) due to its rotation on its axis [4]. As the Earth rotates, it generates a centrifugal force that is strongest at the equator and decreases toward the poles [2]. This outward force causes the Earth's mass to push away from the axis of rotation, resulting in an equatorial bulge where the equatorial radius is approximately 21 to 43 kilometers larger than the polar radius [1]. Consequently, the planet appears slightly flattened at the poles [3]. While the Earth's revolution around the Sun is responsible for seasonal changes, it does not dictate the planet's physical shape; rather, the long-term effects of rotation and the resulting centrifugal force are the primary drivers of its oblateness [1].
Sources
- [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 18: Latitudes and Longitudes > The Shape of The Earth and Latitudinal Heat Zones > p. 241
- [4] https://en.wikipedia.org/wiki/Equatorial_bulge
- [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 7: Tectonics > Forces Behind The Drifting Of Continents (According to Wegener) > p. 95
- [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 3: Interior of the Earth > Force for Drifting > p. 28
SIMILAR QUESTIONS
The Earth is an oblate spheroid and not a perfect sphere. This is because 1. the Earth has a rotational motion and the rotational speed increases as one goes from the Poles towards the Equator. 2. the Equator experiences greater gravitational pull from the Sun. 3. the intensity of sunlight received at the Equator is greater than that at the Poles. Select the correct answer using the code given below:
According to the Geo-scientists, the shape of the earth is: 1. round 2. spherical 3. close to that of a sphere 4. an oblate ellipsoid Select the correct answer using the code given below:
In a group discussion on shape and size of the Earth, three students stated the following points : 1. Student 1 : The shape of the Earth is basically an oblate spheroid. 2. Student 2 : The polar diameter of the Earth is more than the equatorial diameter. 3. Student 3 : Bulge along the equatorial region is due to revolution of the Earth. Who among the above students is /are correct?
The free fall acceleration g increases as one proceeds, at sea level, from the equator toward either pole. The reason is
Assertion (A): The Equatorial regions bulge outwards by about 21 kilometre compared to Poles.
Reason (R): Earth’s slow rotation reduces the effect of gravity around the Equator.