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 free fall acceleration g increases as one proceeds, at sea level, from the equator toward either pole. The reason is
Asked in UPSC NDA 2 2016 · Topic: Mechanics (Gravitation and Central Force Motion (Kepler's Laws))
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Answer: C. Earth is approximately an ellipsoid having its equatorial radius greater than its polar radius by 21 km
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