or in instructables contest rules the area of a cylinder.
Answer to Burning Questions round 6.5, also shows you in a short video
the circumference of a circle and the meaning of pi.
Step 1: The Formula
If you look at textbooks, or formula sheets on an exam you will come across this formula.
A =2 pi r ( r + h ), where Pi is the ratio of the circumference of a circle to it's radius
Step 2: Splitting Up the Shapes
We start by splitting the shape up, imagine you have to make a cylinder out of paper.
What shapes would you use to make a 3D cylinder?
2 circles and a rectangle!
Still don't know how these shapes fit, get some paper, tape and scissors, try it!
Step 3: Area of the Circles
pi x r2
So in simple terms, (special ratio number) multiplied by the radius
of the circle that is squared.
Squared means the number multiplied by itself
*hehe, it is also the anti derivative of perimeter of a circle...co-incidence or is it?
For curious people the next step is a simple lesson on pi (video no reading, yeah!)
Radius, the point from the middle of circle to the outside
Step 4: Origins of Pi, and Circumference
Step 5: Area of the Rectangles
Length multiply by width,
In this case the length of the rectangle is the height, and the width is the circumference.
If you do not know how the circumference is the width, refer to your paper model
and watch my video on the previous step.
The rectangle wraps around the outside of the circle
Formula = h x ( 2 x pi x r)
Step 6: Adding It All Up
So the cylinder is made up of 2 circles and 1 rectangle lets add them up.
Re call: area of 1 circle = pi x r2
area of 1 rectangle = h x 2 x pi x r
remember there are 2 circles so adding up is:
Area = pi x r2 + Pi x r2 + h x 2 x pi x r
circle + circle + rectangle
Simplify: 2 x pi x r2 + 2 x pi x r
Then take out the 2 x pi x r as a common factor:
Area = 2 x pi x r x (r + h)
Step 7: Things You Should Know
Now you have your answer just measure and enter your values of radius and height
and you will find your area of the cylinder.
Things to remember:
- If you find this formula difficult for now, you can always find the areas of the
- radius is the distance from the midpoint of a circle to the outside (not to be confused
- This is the Total surface area not Volume
- pi is more commonly written like it was shown in the video
- pi is irrational (it has many many decimal places), 3.14 is a very basic estimate, for
Step 8: Practical Uses
The area of my can;
radius = 3.5 cm
height = 10.5 cm
Area = 2 x Pi x r x (r + h)
= 2 x 3.14 x 3.5 x (3.5 + 10.5)
(solve brackets first)
Area = 307.72 cm2
(remember your units)
*Surface area of a piston in an engine to find how much friction there is.
*Your a product designer and you want to know the amount of materials needed
for a cylindrical cup holder.
*Enter in this competition, Vote for me!