# Cylinder

*Cylindrical surface. Directrix and generatrices of a cylindrical surface.*

Cylinder. Right cylinder. Oblique cylinder. Circular cylinder. Round

cylinder. Prism as a particular case of a cylinder. Cylindrical sections.

Cylinder. Right cylinder. Oblique cylinder. Circular cylinder. Round

cylinder. Prism as a particular case of a cylinder. Cylindrical sections.

**
Cylindrical surface
**
is a surface, formed by a motion of a straight line (AB, Fig.82 ), which saves the same direction and intersects with
the given line MN ( or a curve ). A line MN is called a

*directrix*. Straight lines, corresponding to different positions of the straight line AB at its motion ( A’B’, A”B” etc. ), are called

*generatrices*of cylindrical surface.

**
Cylinder.
**
A body, limited by cylindrical surface (with a closed directrix) and two parallel planes, is called a

*cylinder*( Fig.83 ). Parts of these planes ( ABCDEFG and

*abcdefg*) are called

*bases*of a cylinder. A distance between the bases ( KM, Fig.83 ) is a

*height*of a cylinder. A cylinder is

*right*, if its generatrices are perpendicular to its base; otherwise, a cylinder is

*oblique*. A cylinder is

*circular*, if its base is a circle. If a cylinder is simultaneously both

*right*and

*circular*, it is called a

*round*cylinder. A prism is a particular shape of a cylinder ( why ? ).

**
Cylindrical sections of a circular cylinder
**

*lateral surface*( Fig.84 ).

*The sections, parallel to a base, are*

**circles**of the same radius. The sections,*parallel to a generatrix of cylinder, are*(AB || CD).

**pairs of parallel straight lines***The sections, which are not parallel both to bases and to*

*generatrix, are*

**ellipses**.