Volume of Cone

Understanding Cones: Definition, Types, and Volume Calculation

When you come across a volcano, does it remind you of a giant ice cream cone? Have you ever wondered how much ice cream could fit inside it? In this article, we will delve into the concept of cones, learn how to calculate their volume, and explore practical applications of these 3D objects.

What is a Cone?
A cone is a solid shape with a circular base and a curved surface that narrows down to a point, known as the apex or vertex. Familiar examples of conical objects include traffic cones, birthday cone hats, and even carrots.

Types of Cones
There are two main types of cones: right circular cones and oblique circular cones. Right circular cones have their apex directly above the center of the base, while oblique circular cones have their apex located elsewhere.

An illustration of a right circular cone

An illustration of an oblique circular cone

Calculating Volume using the Volume of a Cylinder
The volume of a cone is one-third of its corresponding cylinder's volume. This means that if a cone and cylinder have the same base dimensions and height, the cone's volume is one-third of the cylinder's volume. Let's see this in action through a simple experiment.

Step 1. Gather an empty cylinder and cone with known height and base radius.

Step 2. Fill the cone with water until it reaches the brim.

Step 3. Pour the water from the cone into the cylinder and take note of the water level. The cylinder will not be full.

Step 4. Repeat steps 2 and 3 two more times, and observe how the water level in the cylinder rises with each pour. On the third pour, the cylinder will be full.

This experiment shows that it takes three cones to fill one cylinder.

An illustration of the relationship between a cone and cylinder

How to Calculate Cone Volume
To calculate the volume of a cone, we use the formula V=1/3πr²h, where r is the base radius and h is the height.

Example:
A conical cap has a base radius of 7 cm and a height of 8 cm. Find the volume of the cone.

Solution
Given: r=7cm, h=8cm, π=3.14
Volume = 1/3πr²h = 1/3 x 3.14 x 7² x 8 = 1230.88 = 410.29 cm³

Finding Volume when Height is Unknown
If we have a cone with an unknown height, we can use either the slant height or the apex angle to calculate its volume.

If the slant height (l) is known, we can use the Pythagorean theorem to find the height (h). The volume formula remains the same, V=1/3πr²h.

An illustration of a cone with a known slant height

If the apex angle is given, we can use the SOHCAHTOA method to determine the height. Half of the given angle is used in the volume formula, V=1/3πr²h.

An illustration of a cone with a known apex angle

Calculating the Volume of a Frustum of a Cone

A frustum of a cone, also known as a truncated cone, is formed by removing the vertex of a cone. It is a shape commonly found in household items like buckets.

To calculate the volume of a frustum, we use the principle of proportion. A frustum has two radii - one for the larger circular surface and one for the smaller circular surface.

Let's visualize this by imagining a cone with its top cut off to make a frustum.

Let R be the radius of the larger circular surface, r be the radius of the smaller circular surface, hf be the height of the frustum, and H be the height of the complete cone. Also, let hc be the height of the smaller cone that was removed to create the frustum.

Applying the principle of proportion, we have:

Rr = Hhc

The volume of the frustum is equal to the difference between the volume of the complete cone and the smaller removed cone. This can be written as:

Volume of frustum = (1/3)πR²H - (1/3)πr²hc

To calculate the frustum's volume, we need to know the values of R, r, hf, and hc. Let's look at an example:

Example: Finding the Volume of a Frustum

A cone has a base radius of 20 cm and a removed tip-top radius of 8 cm. The frustum has a height of 15 cm. Calculate the frustum's volume.

Solution: We divide the given values by 2 to get the radii for the larger and smaller circular surfaces. Let's label them as R and r.

Given: R=10cm, r=4cm, hf=15cm, hc=?, π=3.14

We can substitute these values into the formula for the volume of the frustum:

Volume of frustum = (1/3)πR²H - (1/3)πr²hc

= (1/3) x 3.14 x 10² x 15 - (1/3) x 3.14 x 4² x ?

= 4712.5 - 83.733 = 4628.767 cm³

Given R = 10 cm, r = 4 cm, and hf = 15 cm, we can find the heights of the complete cone H and the small cut cone hc using the principle of proportion.

Using the formula 10/4 = (15 + hc)/hc, we can solve for hc and get a value of 10 cm.

Now, the volume of the frustum can be calculated using the formula Volume = (1/3)π(10)²(15) - (1/3)π(4)²(10), which gives us a value of 1571.43 cm³.

Conclusion: The frustum has a volume of 1571.43 cm³.

Application

Let's apply the concept of volume of a frustum to solve a new problem.

Problem: A cylinder with a base radius of 4.2 cm and a height of 10 cm has a conical funnel with the same circular top and height placed inside it. Find the volume of the funnel.

Solution: Using the formula for the volume of a cylinder, we can find that the cylinder has a volume of 554.4 cm³. Since the cone has the same height and circular top, its volume is one-third of the cylinder's volume, which is 184.8 cm³.

Key Takeaways

A cone is a three-dimensional solid with a circular base and a curved surface that tapers to a point at the apex.
There are two types of cones - right circular cone and oblique circular cone.
A cone is one-third of a cylinder in terms of volume.
The volume of a cone is one-third of the circular base area multiplied by its height.
A frustum of a cone is formed by cutting off the apex of a cone.

How to Find the Volume of a Cone?

To calculate the volume of a cone, use the formula V = 1/3 × Ab × h, where Ab is the area of the circular base and h is the height.

How to Find the Volume of a Cone Without the Height?

If the angle at the apex of the cone is known, the height can be determined using simple trigonometry. Alternatively, the height can also be found using the Pythagorean theorem if the slant height of the cone is given.