FACTOID # 119: The United States has the world's highest number of McDonald’s restaurants per capita. Americans also die of obesity more often than any other nation, with more deaths than Mexico, Germany, Spain, Austria and Canada combined.
 
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Encyclopedia > Prolate

A spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. If the ellipse is rotated about its major axis, the surface is called a prolate spheroid (similar to the shape of a rugby ball). If the minor axis is chosen, the surface is called an oblate spheroid (similar to the shape of the planet Earth).

Image:ProlateSpheroid.PNG
Prolate spheroid.
Image:OblateSpheroid.PNG
Oblate spheroid.

The sphere is a special case of the spheroid in which the generating ellipse is a circle.


A spheroid is a special case of an ellipsoid where two of the three major axes are equal.


Volume

Prolate spheroid:

  • volume is

Oblate spheroid:

  • volume is

where

  • a is the major axis length
  • b is the minor axis length

Surface area

A prolate spheroid has surface area

An oblate spheroid has surface area

b(b + a·arcsin(e)/e).

Here e is the eccentricity of the ellipse, defined as


  Results from FactBites:
 
Error analysis using ellipsoids. Three-dimensional mathematical analysis of particle shape using x-ray tomography and ... (1565 words)
By this is meant ellipsoids with axes in the ratio of 1:1:5, and 5:5:1.
Figure 10 shows the volume and surface area for a 5:1 prolate ellipsoid as a function of the number of spherical harmonic coefficients used (in terms of N), for an ellipsoid that now has axis dimensions, in terms of voxels, of 11:11:55.
For an aspect ratio of 20, the oblate ratio is 1.085, and the prolate ratio is 1.371.
  More results at FactBites »


 

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