Introduction: Circumference of a Circle

In this Instructable, we will dive into the exciting world of Circles.
Specifically the Circumference of a Circle.

Supplies:
Pencil (needed for it's erase-ability)
Paper
Calculator (to check your answer)

Step 1: Circle

Some basics of the Circle:

Circumference - the distance around the circle (aka the perimeter of the circle)
Radius - the distance from the center to any point on the circle
Diameter - the distance from a point on the circle to another point on the circle going
through the center (also twice the length of the Radius)
Pi - the symbol that represents the value 3.14 (actually Pi is a never ending number, but for our purposes 3.14 will be fine)

Step 2: Circumference

Now to find the Circumference

Formulas for Circumference:
C = 2*Pi*r
C = Pi*d

r - radius
d - diameter

General Steps for solving:
1) write the formula you will use
2) write the information Given
3) substitute the given information into the formula
4) follow your Order of Operations (PEMDAS) to simplify and reduce
5) circle your answer
6) check your answer

Example 1:
Given: circle with a radius = 4 cm
1) C = 2*Pi*r (choose this formula because you are given a radius)
2) r = 4
3) C = 2*Pi*4
4) C = 8*Pi
4) C = 8*3.14
5) C = 25.12 cm (don't forget your units)

Example 2:
Given: circle with a diameter = 12 in.
1) C = Pi*d (choose this formula because you are given a diameter)
2) d = 12
3) C = Pi*12
4) C = 3.14*12
5) C = 37.68 in. (don't forget your units)

Comments

author
TheDoctor11 made it!(author)2013-07-07

3.1415926535897932384626433832795028841961693993751058209749445923078164062862089986280348

author
TheDoctor11 made it!(author)2013-07-07

Ive got 88! Memorized it fir a contest.

3.1415926535897932384626433732795028841971693993751058209749445923078164062862089986280348

Plz tell me if i messed up

author
notanemo made it!(author)2009-10-04

off the top of my head, pi is equal to 3.141592653589793. i have it to a million on my comp

author
mrpesas made it!(author)2010-03-13

I only have it memorized to 3.14159.  I like to show my students the websites that let you search for your b-day, phone number, ss#, etc in pi
like this
http://www.angio.net/pi/piquery

author
joen made it!(author)2010-03-13

in example 2 of step 2 you show that the radius is 12 in. Don't you mean the diameter?

author
mrpesas made it!(author)2010-03-13

You are correct.  Thank you for pointing it out.  I fixed the page. :-)

author
thepelton made it!(author)2010-03-13

I know it's not as precise, but 22/7 works for a close guesstimate.

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