# Relation of a cylinder to a prism

A prism is a solid with bases that are polygons and the sides are flat surfaces. (See Definition of a prism). Strictly speaking a cylinder is not a prism, however it is extremely similar. If you imagine a prism with regular polygons for bases, as you increase the number of sides, the solid gets to look just like a cylinder. So we can say that a cylinder is a prism with an infinite number of faces.

In the applet above, keep clicking on 'more' to see this effect. This is similar to the way a regular polygon turns into a circle when the number of sides gets infinitely large. See Area of a circle derivation.

A cylinder is also similar to a prism in that

1. It has the same cross section anywhere.
2. Its volume is calculated by multiplying the area of a base by the height.
3. It can be right or oblique.

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