The Earth is flattened at the poles and bulged at the equator due to the following reasons:
- Rotation: The Earth rotates around its axis, causing a centrifugal force that acts perpendicular to the axis of rotation. This force is stronger at the equator and weaker at the poles. The centrifugal force at the equator counteracts the force of gravity, causing the equatorial region to bulge outward.
- Centripetal Acceleration: As the Earth rotates, every point on its surface experiences centripetal acceleration towards the axis of rotation. This acceleration is highest at the equator and decreases towards the poles. The resulting inward pull at the poles compresses the Earth, leading to a flattening effect.
- Equilibrium Shape: The Earth seeks an equilibrium shape that balances gravitational attraction and centrifugal force. This equilibrium shape is an oblate spheroid, where the equatorial diameter is larger than the polar diameter. This shape occurs because the centrifugal force causes the material to accumulate at the equator, leading to a bulge, while the polar regions experience a net gravitational contraction, resulting in a flattening.
- Density and Composition Variations: Variations in the density and composition of Earth’s interior can also contribute to the observed shape. The distribution of mass within the Earth, including denser materials towards the core, can influence the overall shape and gravitational field, leading to the polar flattening and equatorial bulge.
These factors combined result in the Earth’s shape being slightly flattened at the poles and bulged at the equator. The deviation from a perfect sphere is relatively small, but it has been measured and confirmed through geodetic surveys and satellite measurements.