newtonian mechanics - Why don't we consider centrifugal force on a mass placed on earth?

Let us say a block of mass is placed on the surface of earth. Then while drawing the forces on that body, we say:

1. Force $F = mg$ acting towards the center of Earth.


2. Normal reaction $N$ offered by the surface of Earth.

If no other forces are acting, we say $F=N$. But what about the centrifugal force $m\omega^2R$ . Why don't we ever bring that into picture? What am I missing?

Answer

Because it's effect is smaller than the variation in $g$ due to earth's bulge (caused by the same centrifugal force) or the local geology - when you use $9.8m/s^2$ that's just an approximation.

The effect of the bulge and centrifugal force mean that $g$ at the equator is about 0.5% lower than $g$ at the poles

edit: velocity at equator $40,000 km / 24 h = 1666.7 km/h = 0.463 km/s$

'centrifugal g' = $(0.463 km/s)^2 )/ 6375 km = 0.03 m/s^2$ or 0.3% of 'g'