You know what 'PI' is ... it's a number with the value 3.14, and it's used to find the circumference and area of a circle.
But did you ever wonder where PI came from? Did somebody make it up? Was it invented? Where does it come from!? 

PI is a truly magical number! The symbol itself is a Greek letter.

It represents the number 3.14159... , a number which has an infinite number of decimal places, with no repeating pattern. (These kinds of numbers are called irrational.) Because there is no predictable pattern to the digits, we can never know all of them. But they can be calculated ... you can see the first 4000 decimal places (!) on our PI page.

But where does the number come from?!?

Imagine drawing some circles. You could draw a really tiny one. Or maybe a bigger one that fills your page. Or perhaps a large one on the blackboard. Even a gigantic one out in the field behind the school.

Now imagine carefully measuring the diameter of each circle, or the distance across the middle , and then each circle's circumference, which is the distance around the outside..

Here's an example:

Divide this circle's circumference by its diameter.
When you do the calculation: 5.18 divided by 1.65 ... 
...the result is the magic number 3.14, or PI!


Let's try it for a bigger circle:

Divide this bigger circle's circumference by its diameter.
When you do the calculation: 40.5 divided by 12.89 ... 
...the result again is the magic number 3.14, or PI!


Let's try it for a really large circle now:


  

Divide this really huge circle's circumference by its diameter.

When you do the calculation: 

960 divided by 305.7

...the result yet again is ... 

the magic number 3.14, or PI!


 
 
 
 


Get the idea? Every circle ever drawn, regardless of its size, will always produce the magic number PI when you divide its circumference by its diameter!

Mathematicians who discovered this, thousands of years ago, were amazed! It's as if the number PI were 'hidden' in every circle, just waiting to be released!

You can find the magic PI number yourself by drawing a circle carefully with a set of compasses. You can measure its diameter easily with a ruler, but to measure the circumference, you'll need a piece of thread to lay around the circle; stretch it out straight to measure it.

With ordinary instruments, it's unlikely you'll be able to get PI to appear with more than two decimal places correct; errors in measurement will make anything after that wrong. But just in case you're very precise, look for the value 3.14159...

Any ideas about how you'd measure a circle outside that would fill the baseball field???


You might also be interested in visiting our page that explains
where the area formula for a circle comes from!