# circumference of the circle

• Aug 18th 2012, 11:31 AM
ariel32
circumference of the circle
from what i understand the circle has a fixed circumference of about 3 meters
how is that possible when you can draw smaller and bigger ones how can the circumference not change according the size you draw?
• Aug 18th 2012, 11:59 AM
earboth
Re: circumference of the circle
Quote:

Originally Posted by ariel32
from what i understand the circle has a fixed circumference of about 3 meters
how is that possible when you can draw smaller and bigger ones how can the circumference not change according the size you draw?

Maybe you've misunderstood something ...

The cirumference of a circle is calculated by $p = \pi \cdot d$, where p means perimeter and d is the diameter of the circle.

Rearranging this equation you'll get $\frac pd = \pi \approx 3.14159$

So maybe you've heard that the ratio of these 2 lengthes is a fixed value of nearly 3.
• Aug 18th 2012, 12:03 PM
HallsofIvy
Re: circumference of the circle
I have no clue what you are talking about. "from what i understand the circle has a fixed circumference of about 3 meters"??? What circle are you talking about? Surely you don't mean "the circle" in the sense of "all circles". Every circle has circumference proportional to its diameter, NOT "fixed". The circumference of a circle is $\pi$ times its diameter. Now $\pi$ is a constant slightly larger than 3 so every circle has circumference "about 3" (but NOT "3 meters") times the diameter of circle. Perhaps $\pi$ is the "about 3" you are thinking of. But, again, $\pi$ is a number, not a measurement, and so has no units such as "meters". And the circumference is that number times the diameter of the circle.

A circle of diameter 1 mm has circumference about 3.14 mm. A circle of diameter 1 light year has circumference about 3.14 light years. Neither of those is anywhere near "3 meters".