Glossary
When you divide the diameter of any circle into the circumference (perimeter)
of that same circle the answer you get will always be the same, 3.14159. This
number is what we call Pi (
).
Because Pi ()
is a constant number, you can use it to find the circumference of any circle
whose diameter we know.
The formula for the circumference of a circle is C=
d (circumference = x
diameter).
A variation of the same formula uses the radius of the circle: C= 2r
(circumference = x 2 x radius). However, in engineering you usually work
with diameter (Ø).
Problem
What length of round bar Ø12mm is required to roll a stiffening ring for the mouth of a concrete mixer bowl if the mixer has a mouth diameter of 600mm?
(Ø means diameter)
The length of bar you need is the circumference of the circle.
The formula is C= d
Substitute d with the diameter measurement.
C = (600)
We know (Pi) is always 3.14159
Substitute the correct value for .
C = 3.14159 x 600
= 1884.95mm
The circumference of the circle is 1884.95.
Therefore you need 1884.95mm of round bar Ø12mm
Complete
this circumference activity sheet (Word 159 kb)
