The moment arm is not constant on the earth's surface. It is the distance from the surface to the rotational axis.
The moment arm is labeled "p" in this figure. It is maximum at the equator where it is equal to the radius of the earth. At the pole it is zero. The maximum centrifugal acceleration is about 3.4 cm/sec/sec. This happens on the equator.
The earth attracts the all matter according to Newton's law of gravitation. On the earth this is almost a constant acceleration of about 980 cm/sec/sec. That means that the maximum rotational effect is about 1/300 of the gravitational attraction.
This causes the earth to bulge out at the equator.
The ratio of the accelerations is close to the ratio of the distortion ( 1/298.25 ) in the earth's shape that results from rotational effect. The distortion in the figure is exaggerated.
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