Mathematics
Grade 8
15 min
Surface area of cylinders and cones
Surface area of cylinders and cones
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1
Introduction & Learning Objectives
Learning Objectives
Identify the components (radius, height, slant height) of cylinders and cones.
Explain the concept of surface area as the total area of all faces of a 3D object.
Apply the formula to calculate the surface area of a cylinder.
Apply the formula to calculate the surface area of a cone.
Use the Pythagorean theorem to find the slant height of a cone when given its radius and height.
Solve real-world problems involving the surface area of cylinders and cones.
Ever wondered how much paint you'd need to cover a giant water tank, or how much paper it takes to make a party hat? 🤔 It's all about surface area!
In this lesson, you'll learn how to calculate the total area of the 'skin' of two common 3D shapes: cylinders and cones. Understandi...
2
Key Concepts & Vocabulary
TermDefinitionExample
Surface AreaThe total area of all the surfaces (faces) of a three-dimensional object. Imagine 'unfolding' the object into a flat pattern (its net) and finding the area of that flat pattern.If you peel the label off a soup can and flatten it, then add the area of the top and bottom circles, you've found the surface area of the can.
CylinderA three-dimensional geometric shape with two parallel circular bases of the same size connected by a curved surface.A can of soda, a battery, or a section of a pipe are all examples of cylinders.
ConeA three-dimensional geometric shape that tapers smoothly from a flat circular base to a point called the apex or vertex.An ice cream cone, a party hat, or a traffic cone are common examples.
Radius (r)The distance from th...
3
Core Formulas
Surface Area of a Cylinder
$SA_{cylinder} = 2\pi r^2 + 2\pi rh$
This formula calculates the total surface area of a cylinder. $2\pi r^2$ represents the area of the two circular bases (top and bottom), and $2\pi rh$ represents the area of the curved rectangular side (where $2\pi r$ is the circumference of the base and $h$ is the height).
Surface Area of a Cone
$SA_{cone} = \pi r^2 + \pi rl$
This formula calculates the total surface area of a cone. $\pi r^2$ represents the area of the circular base, and $\pi rl$ represents the area of the curved lateral surface (where $r$ is the radius and $l$ is the slant height).
Pythagorean Theorem for Slant Height
$l^2 = r^2 + h^2$
When the slant height ($l$) of a cone is not given, but the radius ($r$) and perpendicular height ($h...
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Challenging
A grain silo is a cylinder with a cone on top. The cylinder part has a radius of 5 m and a height of 10 m. The cone on top has the same radius and a slant height of 8 m. What is the total exterior surface area of the silo, including its circular base on the ground? Use π ≈ 3.14.
A.596.6 m²
B.439.6 m²
C.518.1 m²
D.204.1 m²
Challenging
The height (h) of a cylinder is exactly twice its radius (r). Which expression represents the total surface area of this cylinder in terms of 'r' only?
A.6πr²
B.2πr² + 4πr
C.4πr³
D.6πr²
Challenging
A cylindrical water tank with a diameter of 6 meters and a height of 4 meters needs to be painted on all exterior surfaces. If one can of paint covers 50 m² and costs $30, what is the total cost to paint the tank? Use π ≈ 3.14.
A.$60
B.$120
C.$80
D.$90
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