The free fall acceleration g increases as one proceeds, at sea level,

The free fall acceleration g increases as one proceeds, at sea level, from the equator toward either pole. The reason is

Earth is a sphere with same density everywhere
Earth is a sphere with different density at the polar regions than in the equatorial regions
Earth is approximately an ellipsoid having its equatorial radius greater than its polar radius by 21 km
Earth is approximately an ellipsoid having its equatorial radius smaller than its polar radius by 21 km
This question was previously asked in
UPSC NDA-2 – 2016
The correct answer is C. The primary reasons for the variation of the free fall acceleration ‘g’ with latitude at sea level are the Earth’s shape and its rotation.
The Earth is not a perfect sphere but is approximately an oblate spheroid, bulging at the equator and flattened at the poles. This means the distance from the center of the Earth is greater at the equator than at the poles. The gravitational acceleration ‘g’ is inversely proportional to the square of the distance from the center of the Earth. Therefore, points at the equator are further from the center, resulting in a weaker gravitational pull compared to the poles. Additionally, the Earth’s rotation creates a centrifugal force that opposes gravity, and this force is strongest at the equator and zero at the poles. This centrifugal effect further reduces the effective ‘g’ at the equator compared to the poles. Option C correctly states that the Earth is approximately an ellipsoid with the equatorial radius greater than the polar radius, which is the key geological reason for the variation in ‘g’.
The difference between the equatorial and polar radii is approximately 21 km. The average value of ‘g’ at sea level is about 9.80665 m/s². It is minimum at the equator (approx. 9.78 m/s²) and maximum at the poles (approx. 9.83 m/s²). The effect of Earth’s shape (distance from center) accounts for about two-thirds of the variation, while the effect of rotation (centrifugal force) accounts for about one-third.
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