The earth is a lot bigger than a roundabout so the curve is less steep. the earth turns in 24 hours and is about 25 thousand miles around its circumference so the speed at the equator is about 1000 miles an hour. the centrifugal forece means that the acceleration due to gravity is slightly less at the equator than the poles.

For a circular orbit just above the equator the centrifugal force just balances out the acceleration due to gravity. to do this you need a velocity of about 18,000 mph

The formula for centrifugal force is the square of the velocity divided by the radius of the curve.

The formula for calulating the acceleration due to gravity (in cm/sec^2)at any point on the earth's surface (from Child's physical constants) is:-

g = 980.616 - 2.5928 cos 2xlatitude + 0.0068 cos^2xlatitude - 0.0003 x height in meteres (above sea level)

The first correction of about 2.6/980 or 0.25% is the main bit due to the centrifugal force.

You can confirm the self consitancy of these three facts by noting that the increase in vlelocity between the earth's rotation and the orbit is about 20 and 20x20 is 400 or and 1/400 is 0.25%.

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