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[parent] cylinder (Topic)

When a straight line moves in the space without changing its direction, the ruled surface it sweeps is called a cylindrical surface (or, in some special cases, simply a cylinder). Formally, a cylindrical surface $ S$ is a ruled surface with the given condition:

If $ p,\,q$ are two distinct points in $ S$, and $ l$ and $ m$ are the rulings passing through $ p$ and $ q$ respectively, then $ l \parallel m$ (this includes the case when $ l = m$).
If the moving line returns to its starting point, the cylindrical surface $ S$ is said to be closed. In other words, if we take any plane $ \pi$ perpendicular to any of its rulings, and observe the curve $ c$ of intersection of $ \pi$ and $ S$, then $ S$ is closed if $ c$ is a closed curve.
Figure 1: A closed cylindrical surface
\includegraphics{cylinder.eps}

The solid bounded by a closed cylindrical surface and two parallel planes is a cylinder. The portion of the surface of the cylinder belonging to the cylindrical surface is called the lateral surface or the mantle of the cylinder and the portions belonging to the planes are the bases of the cylinder.

The bases of any cylinder are congruent. The line segment of a generatrix between the planes is a side line of the cylinder. All side lines are equally long. If the side lines are perpendicular to the planes of the bases, one speaks of a right cylinder, otherwise of a skew cylinder.

The perpendicular distance of the planes of the bases is the height of the cylinder. The volume ($ V$) of the cylinder equals the product of the base area ($ A$) and the height ($ h$):

$\displaystyle V = Ah$
If the base is a polygon, the cylinder is called a prism (which is a polyhedron). The faces of the mantle of a prism are parallelograms. If also the bases of a prism are parallelograms, the prism is a parallelepiped. If the faces of the mantle of a prism are rectangles, one speaks of a right prism, otherwise of a skew prism.

For any integer $ n \ge 3$, the following are equivalent statements about a prism $ P$:

  1. $ P$ has a base that is an $ n$-gon;
  2. $ P$ has $ n+2$ faces;
  3. $ P$ has $ 2n$ vertices;
  4. $ P$ has $ 3n$ edges.

Note. The notion of the prism (or cylinder) of a polygon in $ \mathbb{R}^3$ has a higher-dimensional analogue. Given any polytope $ P$, the prism of P is the polytope Prism$ (P) := P\!\times\![0,\,1]$. The vertices of Prism$ (P)$ are the points $ (x,\,0)$ and $ (x,\,1)$, where $ x$ ranges over the vertices of $ P$. In other words, we drag $ P$ a short distance through a vector orthogonal to everything in $ P$, just as we would to obtain the prism of a polygon.



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"cylinder" is owned by stevecheng. [ full author list (4) | owner history (1) ]
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See Also: parallelotope

Also defines:  cylindrical surface, lateral surface, mantle, base, side line, right cylinder, skew cylinder, prism, parallelepiped, right prism, skew prism

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cylindroid (Definition) by PrimeFan
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Cross-references: orthogonal, vector, polytope, edges, vertices, the following are equivalent, integer, rectangles, parallelograms, faces, polyhedron, polygon, height, area, product, volume, distance, generatrix, line segment, congruent, bases, surface, parallel planes, solid, closed curve, intersection, curve, perpendicular, plane, passing through, rulings, points, ruled surface, line, straight
There are 47 references to this entry.

This is version 9 of cylinder, born on 2005-08-26, modified 2007-04-19.
Object id is 7345, canonical name is Cylinder.
Accessed 18336 times total.

Classification:
AMS MSC: 51M04 (Geometry :: Real and complex geometry :: Elementary problems in Euclidean geometries)
 51M20 (Geometry :: Real and complex geometry :: Polyhedra and polytopes; regular figures, division of spaces)
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