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11.4: Cylinders

Difficulty Level: At Grade / Basic / Advanced Created by: CK-12
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What if you wanted to figure out how much paper you needed for the label of a can? How could you use the surface area of a cylinder to help you? After completing this Concept, you'll be able to answer questions like this one.

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CK-12 Foundation: Chapter11CylindersA

Brightstorm: Surface Area of Cylinders

Brightstorm: Volume of Cylinders

Guidance

A cylinder is a solid with congruent circular bases that are in parallel planes. The space between the circles is enclosed. Just like a circle, the cylinder has a radius for each of the circular bases. Also, like a prism, a cylinder can be oblique, like the one to the right.

Surface Area

Surface area is the sum of the areas of the faces. Let’s find the net of a right cylinder. One way for you to do this is to take a label off of a soup can or can of vegetables. When you take this label off, we see that it is a rectangle where the height is the height of the cylinder and the base is the circumference of the base. This rectangle and the two circular bases make up the net of a cylinder.

From the net, we can see that the surface area of a right cylinder is

& \ \underbrace{2 \pi r^2} \qquad + \qquad \underbrace{2 \pi r} h\\&\text{area of} \qquad \qquad \ \text{length}\\& \ \text{both} \qquad \qquad \quad \ \ \text{of}\\&\text{circles} \qquad \qquad \text{rectangle}

Surface Area of a Right Cylinder: If r is the radius of the base and h is the height of the cylinder, then the surface area is SA=2 \pi r^2+2 \pi rh.

To see an animation of the surface area, click http://www.rkm.com.au/ANIMATIONS/animation-Cylinder-Surface-Area-Derivation.html, by Russell Knightley.

Volume

Volume is the measure of how much space a three-dimensional figure occupies. The basic unit of volume is the cubic unit: cubic centimeter (cm^3), cubic inch (in^3), cubic meter (m^3), cubic foot (ft^3), etc. Each basic cubic unit has a measure of one for each: length, width, and height. The volume of a cylinder is V=(\pi r^2)h, where \pi r^2 is the area of the base.

Volume of a Cylinder: If the height of a cylinder is h and the radius is r, then the volume would be V=\pi r^2 h.

If an oblique cylinder has the same base area and height as another cylinder, then it will have the same volume. This is due to Cavalieri’s Principle, which states that if two solids have the same height and the same cross-sectional area at every level, then they will have the same volume.

Example A

Find the surface area of the cylinder.

r = 4 and h = 12. Plug these into the formula.

SA & = 2 \pi (4)^2 + 2 \pi (4)(12)\\& = 32 \pi + 96 \pi\\& = 128 \pi

Example B

The circumference of the base of a cylinder is 16 \pi and the height is 21. Find the surface area of the cylinder.

If the circumference of the base is 16 \pi, then we can solve for the radius.

2 \pi r& = 16 \pi\\r & =8

Now, we can find the surface area.

SA& = 2 \pi (8)^2+(16 \pi)(21)\\& = 128 \pi + 336 \pi\\& = 464 \pi

Example C

Find the volume of the cylinder.

If the diameter is 16, then the radius is 8.

V=\pi 8^2 (21)=1344 \pi \ units^3

Watch this video for help with the Examples above.

CK-12 Foundation: Chapter11CylindersB

Vocabulary

A cylinder is a solid with congruent circular bases that are in parallel planes. The space between the circles is enclosed. A cylinder has a radius and a height and can also be oblique (slanted).

Surface area is a two-dimensional measurement that is the sum of the area of the faces of a solid. Volume is a three-dimensional measurement that is a measure of how much three-dimensional space a solid occupies.

Guided Practice

1. Find the volume of the cylinder.

2. If the volume of a cylinder is 484 \pi \ in^3 and the height is 4 in, what is the radius?

3. Find the volume of the solid below.

Answers:

1. V=\pi 6^2 (15)=540\pi \ units^3

2. Substitute what you know to the volume formula and solve for r.

484 \pi & = \pi r^2 (4)\\121& = r^2\\11 & = r

3. This solid is a parallelogram-based prism with a cylinder cut out of the middle. To find the volume, we need to find the volume of the prism and then subtract the volume of the cylinder.

V_{prism} & =(25 \cdot 25)30=18750 \ cm^3\\V_{cylinder} & = \pi (4)^2 (30)=480\pi \ cm^3

The total volume is 18750 - 480\pi \approx 17242.04 \ cm^3.

Practice

  1. The lateral surface area of a cylinder is what shape? What is the area of this shape?
  2. A right cylinder has a 7 cm radius and a height of 18 cm. Find the surface area and volume.

Find the surface area and volume of the following solids. Leave answers in terms of \pi.

Find the value of x, given the surface area.

  1. SA = 1536 \pi \ units^2
  2. The area of the base of a cylinder is 25 \pi \ in^2 and the height is 6 in. Find the lateral surface area.
  3. The circumference of the base of a cylinder is 80 \pi \ cm and the height is 36 cm. Find the total surface area.
  4. The lateral surface area of a cylinder is 30 \pi \ m^2. What is one possibility for height of the cylinder?
  5. Charlie started a business canning artichokes. His cans are 5 in tall and have diameter 4 in. If the label must cover the entire lateral surface of the can and the ends must overlap by at least one inch, what are the dimensions and area of the label?
  6. Find an expression for the surface area of a cylinder in which the ratio of the height to the diameter is 2:1. If x is the diameter, use your expression to find x if the surface area is 160\pi.
  7. Two cylinders have the same surface area. Do they have the same volume? How do you know?
  8. A can of soda is 4 inches tall and has a diameter of 2 inches. How much soda does the can hold? Round your answer to the nearest hundredth.
  9. A cylinder has a volume of 486 \pi \ ft.^3. If the height is 6 ft., what is the diameter?
  10. The area of the base of a cylinder is 49 \pi \ in^2 and the height is 6 in. Find the volume.
  11. The circumference of the base of a cylinder is 80 \pi \ cm and the height is 15 cm. Find the volume.
  12. The lateral surface area of a cylinder is 30\pi \ m^2 and the circumference is 10\pi \ m. What is the volume of the cylinder?

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Difficulty Level:

At Grade

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Date Created:

Jul 17, 2012

Last Modified:

Apr 17, 2014
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