Why is Earth slightly flattened at the poles and wider at the Equator?

Earth is not a perfect sphere; rather, it is an oblate spheroid. This shape is primarily the result of the planet’s rotation on its axis.1

As Earth spins, it generates a centrifugal force that acts outward from the axis of rotation. This force is strongest at the Equator, where it pushes the planet's mass outward, causing it to bulge. Conversely, there is no centrifugal force at the poles, which results in the planet being slightly flattened in those regions.123

While the gravitational force of Earth’s mass works to pull all material toward the center to create a spherical shape, the constant rotation creates this equatorial bulge, making the planet an oblate spheroid rather than a perfect sphere.143