Definition:Envelope/Solid Geometry
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Definition
An envelope is a surface which is tangent to every element of a given set of surfaces.
Examples
Spheres with Centers on Sphere
Let $\SS$ be a sphere with radius $r$ with center at $O$.
Let $\FF$ be the set of spheres with radius $a$ whose centers all lie on the surface of $\SS$.
Then the envelope of $\FF$ consists of:
- a sphere with radius $r + a$ with center at $O$
- a sphere with radius $\size {r - a}$ with center at $O$.
Also see
- Results about envelopes can be found here.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): envelope: 2.
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): envelope: 2.