# Estimation of Equatorial Bulge of the Earth [duplicate]

My dynamics lecture notes repeat the Earth's equatorial bulge can be approximated as: $$\approx \frac{\Omega^2R}{g} \approx \frac{1}{300}$$ (Do they mean R/300?)

They also include statements like:

"The Earth's oblateness $\frac{I_3-I_1}{I_1}\approx \frac{\Omega^2R}{g} \approx \frac{1}{300}$"

Could anybody explain where this comes from? I have tried several ways to balance the gravitational and centripetal forces but I never seem to arrive at the correct result and cannot get my head around this concept.

## marked as duplicate by Qmechanic♦Mar 26 '18 at 20:52

• Please keep this. The prior answers are exceptionally detailed, and this dimensional/order-of-magnitude estimate is very good (most Datum have an inverse flattening: $298 < 1/f < 301$). – JEB Mar 26 '18 at 23:28