Let us say a block of mass is placed on the surface of earth. Then while drawing the forces on that body, we say:
- Force F=mg acting towards the center of Earth.
- 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 mω2R . 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/s2 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 40,000km/24h=1666.7km/h=0.463km/s
'centrifugal g' = (0.463km/s)2)/6375km=0.03m/s2 or 0.3% of 'g'
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