Q.At which place on the Earth's surface is the gravitational acceleration minimum? Why?

[!TLDR] Gravitational acceleration is minimum at the equator, where the rotational reduction is largest and the equatorial radius (hence distance from the centre) is largest. [!ANSWER] At the equator, beca …

At the equator, both effects that reduce g reach their MAXIMUM: the Earth's rotational centripetal-force requirement is largest here, since a point on the equator traces the largest possible circle (radius R) as the Earth spins, giving the biggest reduction $R\omega^2\cos^2(0)=R\omega^2$; and the equatorial bulge means the equatorial radius is the LARGEST of any latitude, so points there are farthest from the Earth's centre, giving the smallest $GM/r^2$ of any latitude by the shape effect alone. With both the rotation reduction and the shape reduction acting together and both being maximal at the equator, gravitational acceleration rea …

Identify that both reducing effects (rotation, oblate shape) reach their own maximum precisely at the equ …

Assuming only ONE of the two effects matters, missing that they reinforce each other at the equator (both m …