A right circular cylinder is a cylinder whose generatrices are perpendicular to the bases. Thus, in a right circular cylinder, the generatrix and the height have the same measurements. It is also less often called a cylinder of revolution, because it can be obtained by rotating a rectangle of sides r {\displaystyle r} and g {\displaystyle g} around one of its sides. Fixing g {\displaystyle g} as the side on which the revolution takes place, we obtain that the side r {\displaystyle r} , perpendicular to g {\displaystyle g} , will be the measure of the radius of the cylinder. In addition to the right circular cylinder, within the study of spatial geometry there is also the oblique circular cylinder, characterized by not having the generatrices perpendicular to the bases.
Elements of the right circular cylinder Bases: the two parallel and congruent circles of the bases; Axis: the line determined by the two points of the centers of the cylinder's bases; Height: the distance between the two planes of the cylinder's bases; Generatrices: the line segments parallel to the axis and that have ends at the points of the bases' circles.
Lateral and total areas
The lateral surface of a right cylinder is the meeting of the generatrices. It can be obtained by the product between the length of the circumference of the base and the height of the cylinder. Therefore, the lateral surface area is given by:
L = 2 π r h {\textstyle L=2\pi rh} . Where:
L {\displaystyle L\,} represents the lateral surface area of the cylinder;
π {\displaystyle \pi \,} is approximately 3.14159;
r {\displaystyle r\,} is the distance between the lateral surface of the cylinder and the axis, i.e. it is the value of the radius of the base;
h {\displaystyle h\,} is the height of the cylinder;
2 π r {\displaystyle 2\pi r} is the length of the circumference of the base, since π = C 2 r {\displaystyle \pi ={\frac {C}{2r}}} , that is, C = 2 π r {\displaystyle C=2\pi r} . Note that in the case of the right circular cylinder, the height and the generatrix have the same measure, so the lateral area can also be given by:
L = 2 π r g {\displaystyle L=2\pi rg} . The area of the base of a cylinder is the area of a circle (in this case, we define that the circle has a radius with measure r {\displaystyle r} ):
B = π r 2 {\displaystyle B=\pi r^{2}} . To calculate the total area of a right circular cylinder, you simply add the lateral area to the area of the two bases:
A = L + 2 ⋅ B {\displaystyle A=L+2\cdot B} . Replacing L = 2 π r h {\displaystyle L=2\pi rh} and B = π r 2 {\displaystyle B=\pi r^{2}} , we have:
A = 2 π r h + 2 π r 2 {\displaystyle A=2\pi rh+2\pi r^{2}} ⇒ A = 2 π r ( h + r ) {\displaystyle \Rightarrow A=2\pi r(h+r)}
or even
A = 2 π r ( g + r ) {\displaystyle A=2\pi r(g+r)} .
Volume
Cavalieri's principle states that if two solids of the same height and congruent base areas, are positioned on the same plane, such that any other plane parallel to this plane sections both solids, determining from this section two polygons with the same area, then the volume of the two solids will be the same. One can use Cavalieri's principle to determine the volume of the cylinder. This is because the volume of a cylinder can be obtained in the same way as the volume of a prism with the same height and the same area of the base. Therefore, simply multiply the area of the base by the height:
V = B ⋅ h {\displaystyle V=B\cdot h} . Since the area of a circle of radius r {\displaystyle r\,} , which is the base of the cylinder, is given by B = π r 2 {\displaystyle B=\pi r^{2}} it follows that:
V = π r 2 h {\displaystyle V=\pi r^{2}h}
or even
V = π r 2 g {\displaystyle V=\pi r^{2}g} .
Equation in Cartesian analytic geometry The traditional representation of right circular cylinders in 3D analytic geometry uses the equation
x 2 + y 2 = r 2 {\displaystyle x^{2}+y^{2}=r^{2}}
with
0 ≤ z ≤ h {\displaystyle 0\leq z\leq h}
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