为啥 “地球的两极稍扁赤道略鼓，和自转有关”？

地球自转产生的离心力在赤道处最大（因自转半径最大），使赤道地区的物质向外凸起；而两极地区离心力最小，物质相对集中，形成 “两极稍扁、赤道略鼓” 的扁球体形状。这种形状差异虽小（赤道半径比极半径长约 0.3%），但对卫星轨道和地球引力场分布有显著影响。

Why are "the Earth's poles slightly flat and the equator slightly bulging, which is related to rotation"?

The centrifugal force generated by the Earth's rotation is the largest at the equator (due to the largest rotation radius), causing materials in the equatorial region to bulge outward; while the centrifugal force in the polar regions is the smallest, and materials are relatively concentrated, forming an oblate spheroid shape with "slightly flat poles and slightly bulging equator". Although this shape difference is small (the equatorial radius is about 0.3% longer than the polar radius), it has a significant impact on satellite orbits and the distribution of the Earth's gravitational field.