Cylinder

A cylinder is one of the basic shapes in 3D geometry. It has two parallel circular bases set at a distance from each other. The two circular bases are joined by a curved surface at a fixed distance from the center.

The circles and their interiors are called the bases. The radius of the cylinder is the radius of the base. The perpendicular segment from the plane of one base to the plane of the other base is called the altitude of the cylinder. The height of the cylinder is the length of the altitude.

The axis of a cylinder is the segment that contains the centers of the two bases. When the axis is perpendicular to the planes of the two bases, you have a right cylinder. If not, you have an oblique cylinder.

Properties of a cylinder

Each shape has properties that differentiate it from other shapes. Cylinders have the following characteristics:

• The bases are congruent and parallel.
• If the axis forms a right angle with the bases, which are exactly over each other, it is called a "right cylinder".
• It is similar to the prism because all cross sections perpendicular to its altitude are identical.
• If the bases are not directly over each other but still parallel, the axis does not produce a right angle to the bases and it is called an "oblique cylinder".
• If the bases are circular in shape, it is called a "circular cylinder".
• If the bases are an elliptical shape, it is called an "elliptical cylinder".

Measuring the surface area of a cylinder

In order to find the surface area of a cylinder, we need to consider its 3 outward faces, the two bases, and the tube that connects them.

Since the base of a cylinder is a circle, its area is πr2 where r is the radius of the base of the cylinder.

We also need to consider the tube part, which we call the lateral surface area. Note that you can unroll the tube into a rectangle with height h, and base $2\pi \left(r\right)$ (the circumference of the circular base). This gives us an area of $\left(\mathrm{LSA}\right)=2\pi \left(r\right)\left(h\right)$ .

This means that the total area is the two circles plus the tube, or:

${\mathrm{SA}}_c=2\pi r^2+2\pi rh$

Example 1:

Find the lateral surface area of a cylinder with a base radius of 3 inches and a height of 9 inches.

$\mathrm{LSA}=2\pi \left(3\right)\left(9\right)$

$=54\pi {\mathrm{in}}^2$

Approximately $169.56{\mathrm{in}}^2$

Example 2:

Find the total surface area of a cylinder with a base radius of 5 inches and a height of 7 inches.

$\mathrm{SA}{C}_{}=2\pi \left(5\right)\left(7\right)+2\pi {\left(5\right)}^2$

$=70\pi +50\pi$

$=120\pi {\mathrm{in}}^2$

Approximately $376.8{\mathrm{in}}^2$

Finding the volume of a cylinder

If we wanted to find the volume of a cylinder, we must multiply the area of the base by the height of the cylinder. The formula is:

$V=\pi r^{2}h$

Example 3

Find the volume of a cylinder with a radius of 3 cm and a height of 10 cm.

$V=\pi {\left(3\right)}^2\left(10\right)$

$V=90\pi {\mathrm{cm}}^3$

Approximately $282.6{\mathrm{cm}}^3$

Topics related to the Cylinder

Perimeter, Area and Volume

Volume of a Cylinder

Circle

Flashcards covering the Cylinder

8th Grade Math Flashcards

Common Core: 8th Grade Math Flashcards

Practice tests covering the Cylinder

MAP 8th Grade Math Practice Tests

8th Grade Math Practice Tests

Get help learning about cylinders

Working with cylinders is an important part of your student's geometry lessons. However, it can be tricky to keep all the formulas for lateral surface area, total surface area, and volume straight. If your student needs help working with cylinders and their formulas, have them work individually with a professional math tutor. An expert math tutor can provide the kind of 1-on-1 attention that is lacking in a classroom in an environment free from distractions so your student can focus on the lessons. Your student can ask their tutor questions as soon as they arise so they learn the right info from the start. A tutor can use techniques that cater to your student's learning style as well. To learn more about how tutoring can help your student with cylinders and other 3D objects, contact the Educational Directors at Varsity Tutors today.