The earth bulges out at the equator, why?

This is due to the shape of the earth. The earth is not a true sphere but it is an ellipron. The equatorial diameter of the earth is 12756.2711 km. While it’s polar diameter is 12713.5 km. The difference between its equatorial & polar diameter is about 43 kilometers the rotation the earth on its axis produces as centrifugal force which increases its equatorial diameter.

Due to this reason the earth bulges at the equators.