Lesson 15The Volume of a Cone
Learning Goal
Let’s explore cones and their volumes.
Learning Targets
I can find the volume of a cone in mathematical and real-world situations.
I know the formula for the volume of a cone.
Lesson Terms
- cone
- cylinder
- sphere
Warm Up: Which Has a Larger Volume?
Problem 1
The cone and cylinder have the same height, and the radii of their bases are equal.
Which figure has a larger volume?
Do you think the volume of the smaller one is more or less than
the volume of the larger one? Explain your reasoning. Here is a method for quickly sketching a cone:
Draw an oval.
Draw a point centered above the oval.
Connect the edges of the oval to the point.
Which parts of your drawing would be hidden behind the object? Make these parts dashed lines.
Sketch two different sized cones. The oval doesn’t have to be on the bottom! For each drawing, label the cone’s radius with
and height with .
Activity 1: From Cylinders to Cones
Problem 1
A cone and cylinder have the same height and their bases are congruent circles.
If the volume of the cylinder is 90 cm³, what is the volume of the cone?
If the volume of the cone is 120 cm³, what is the volume of the cylinder?
If the volume of the cylinder is
, what is the volume of the cone? Either write an expression for the cone or explain the relationship in words.
Activity 2: Calculate That Cone
Problem 1
Here is a cylinder and cone that have the same height and the same base area.
What is the volume of each figure? Express your answers in terms of
Problem 2
Here is a cone.
What is the area of the base? Express your answer in terms of
. What is the volume of the cone? Express your answer in terms of
.
Problem 3
A cone-shaped popcorn cup has a radius of 5 centimeters and a height of 9 centimeters. How many cubic centimeters of popcorn can the cup hold? Use 3.14 as an approximation for
Are you ready for more?
Problem 1
A grain silo has a cone shaped spout on the bottom in order to regulate the flow of grain out of the silo. The diameter of the silo is 8 feet. The height of the cylindrical part of the silo above the cone spout is 12 feet while the height of the entire silo is 16 feet.
How many cubic feet of grain are held in the cone spout of the silo? How many cubic feet of grain can the entire silo hold?
Lesson Summary
If a cone and a cylinder have the same base and the same height, then the volume of the cone is
The cylinder has a volume of
If the radius for both is