Here is a circle. Points , , , and and segments and are drawn.
What is the area of the circle, in square units? Select all that apply.
approximately 25
approximately 50
If the area of a circle is square units, what is its radius? Explain your reasoning.
11.2
Activity
Circular Volumes
What is the volume, in cubic units, of each figure? Even if you aren’t sure, make a reasonable guess.
Figure A: a rectangular prism whose base has an area of 16 square units and whose height is 3 units
A
Figure B: a cylinder whose base has an area of 16 square units and whose height is 1 unit
B
Figure C: a cylinder whose base has an area of 16 square units and whose height is 3 units
C
11.3
Activity
A Cylinder's Dimensions
For cylinders A–D, sketch a radius and the height. Label the radius with an and the height with an .
Earlier you learned how to sketch a cylinder. Sketch cylinders for E and F, and label each one’s radius and height.
11.4
Activity
A Cylinder's Volume
Here is a cylinder with height 4 units and diameter 10 units.
Shade the cylinder’s base.
What is the area of the cylinder’s base? Express your answer in terms of .
What is the volume of this cylinder? Express your answer in terms of .
A silo is a cylindrical container that is used on farms to hold large amounts of goods, such as grain. On a particular farm, a silo has a height of 30 feet and diameter of 12 feet. Make a sketch of this silo, and label its height and radius. How much volume, in cubic feet, does this silo hold? Use 3.14 as an approximation for .
Student Lesson Summary
We can find the volume of a cylinder with radius and height using two ideas we've seen before:
The volume of a rectangular prism is the result of multiplying the area of its base by its height.
The base of the cylinder is a circle with radius , so the base area is .
Remember that is the number we get when we divide the circumference of any circle by its diameter. The value of is approximately 3.14.
Just like a rectangular prism, the volume of a cylinder is the area of the base times the height. For example, consider a cylinder whose radius is 2 cm and whose height is 5 cm.
The base has an area of cm2 (since ), so the volume is cm3 (since ). Using 3.14 as an approximation for , we can say that the volume of the cylinder is approximately 62.8 cm3.
In general, the base of a cylinder with radius units has area square units. If the height is units, then the volume in cubic units is
Glossary
None
Have a correction or suggestion?
Tell us about a typo, a broken link, or an improvement you’d like to see. We read every submission but can’t reply.