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Contact Angle


The Angle $\alpha$ between the normal vector of a Sphere (or other geometric object) at a point where a Plane is tangent to it and the normal vector of the plane. In the above figure,

$\displaystyle \alpha$ $\textstyle =$ $\displaystyle \cos^{-1}\left({a\over R}\right)$  
  $\textstyle =$ $\displaystyle \sin^{-1}\left({R-h\over R}\right).$  

See also Spherical Cap

© 1996-9 Eric W. Weisstein