MadSci Network: Physics
Query:

Re: How do you determine 'excess radius'

Date: Sun May 15 23:45:07 2005
Posted By: Jay Shapiro, Staff, Engineering, TA Aerospace
Area of science: Physics
ID: 1114902526.Ph
Message:

If I understand Dan Mayer's response correctly, I think that he was making 
an analogy comparing the greater complexity of the sphere of the earth to a 
 simple circle (a slice through the equator).

That being said, the "excess radius" would be caused by the fact that the 
earth is not a perfect sphere. Using the volume or surface area 
equations that he gave, and solving for 'R'(using the actual surface area 
(or volume) of the earth)would give the AVERAGE RADIUS of the earth.

The actual radius of the earth, say, in the town where you live, would of 
course be a length from the surface to the exact center of the earth. This 
radius would change from locations north or south of this spot.  This is 
because the 'sphere' of the earth bulges at the equator.

If you took the AVERAGE radius of the earth, measured from all spots on the 
surface,  and used this value for 'R' in the equation he gave for surface 
area: Area = 4 pi R ^2 , the numbers should equal out with no "excess 
radius"

I hope that this makes it a little clearer.

Jay Shapiro


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