What is pi?    

 It's not just a Greek letter. 
Did you know that no matter what size the CIRCLE:

If you divide its Circumference by it's diameter

 you will get pi (3.14),  

 o     O  o     O       

Well how do you find the  CIRCUMFERENCE (C) of a CIRCLE?               (distance around)

       And how do you find the DIAMETER (d)  OF A CIRCLE?                       (distance across)

O

1. fIRST FIND THE DIAMETER:  You need a ruler, and a Circle.  Measure straight across the center of the circle:  that's the diameter

2..  SECOND USE THE CIRCUMFERENCE formula (it works, trust me).

        Circumference = diameter * pi    (C = d * pi)

 Well what is pi?    You tell me!!                                                      (I'm confused)

(pi = 3.14)                                                          IF                                                             

  C = d * pi     [Algebra]  THEN   pi = C/d  (you divided both sides by d)

                             

Try it!!   

     Start Here:

               Measuring across a circle with a ruler-- you get 10 centimeters.     (diameter)

        

                If  you GOOGLE  "pi"    you get  3.1415...

         WE JUST USE  3.14 = pi        OK?

   diameter = 10 centimeters (cm)   and pi = 3.14

C = d* pi

Circumference = diameter * pi

C = 10 cm * 3.14  (do the math)

10 cm * 3.14  =   31.4 cm

     

SO THIS CIRCLE HAS A CIRCUMFERENCE OF 31.4 centimeters (cm)?

YES

 (Why?    because... you need to go back and find out)

          NOW THE FUN STUFF:    

                                     
pi  =  Circumference

                                             diameter                       (YES! see above)

       Three CIRCLES: 

#1. circumference is 6.28 cm  and diameter is  2 cm

                   

               6.28 cm/2cm  = 3.14

 

 

#2. circumference is 18.6 cm  and diameter is   6 cm

                    

                 18.6 cm  = 3.14    

6 cm

   

#3. circumference is  15.5 cm   and diameter is  5 cm

  

                  15.5 cm   = 3.14

   5 cm

 ITS A CIRCLE: 

C = d * pi                   C / d = pi

     

      So, who cares?   Well, this is where they got pi. And it works for any circle.   Pi is called a ratio because ratio means divide and you divide Circumference of a circle by its diameter to get pi.                                

 

                    Voila!     A Ratio         (...and remember, a fraction is just a division problem...)