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Learning About Pi
The word “pi” doesn’t refer to something
grandma bakes in the oven with apples, although we usually pronounce it
the same way. No, pi is a number. It’s a particular number that
has great importance in math, science and engineering. Which number?
3.1415926535897932…
You notice the three dots at the end there? Well, pi
actually goes on forever without repeating itself. That’s right,
forever. For that reason we call it an “irrational number.”
So don’t try to argue with it. You probably won’t need to
know 16 digits like you see there. Most people just remember 3.14159,
or even more simply, 3.14.
That’s why “Pi Day” is celebrated on
March 14th. Third month, fourteenth day. Pi Day can be a whole lot of
fun and there are hundreds of different activities you can do to celebrate
this amazing number. (See resources below)
Calculating Pi
So what exactly is pi? It’s the ratio of the circumference
of a circle to its diameter. Huh? OK, here it is more simply: if a circle
is one inch across the middle, then it is 3.14 inches around the outside.
And it doesn’t matter how big the circle is, that ratio will stay
the same.
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The formula for finding the circumference
of a circle is:
C = dπ or C = 2πr
where d = diameter and r = radius
Click
here to download an activity on pi and circumference |
“Pi” is actually a letter in the Greek alphabet. In Greek,
that letter is written like this: π. It’s the equivalent
of the English letter “P.” We now use that symbol for pi
in mathematics. The reason we use the letter “pi” is that
it’s the first letter in the Greek word for perimeter. You see,
perimeter basically means circumference.
History of Pi
We only started saying pi and using that funny letter in the 18th
century, but people have known about the idea of pi for a long long
time. The ancient Babylonians and Egyptians knew that this kind of constant
number existed, although their calculations were a bit off. Archimedes
of Syracuse (not the University but the place in ancient Greece) discovered
pi in the third century BC and Zu Changzhi did the same in the 5th century
AD, without knowing about Archimedes work.
Digits of Pi
We mentioned that pi goes on forever without repeating itself, but
people have always been interested in learning as many digits as possible.
With computers this has become easier. In 2002 a professor at the University
of Tokyo calculated pi to 1.24 trillion digits. And there have always
been people who’ve tried memorizing as much of pi as possible.
The current world record was set in 2005, when Lu Chao of China recited
pi correctly to 67,890 digits. It took him over 24 hours to say it!
Activities
- See where your birthday falls in pi. Use the Pi
Searcher to help you. You can also find other combinations of numbers.
- Memorize the first One
Million Digits of Pi. OK, just kidding. However, if you're interested
in seeing what one million digits looks like, then check out this link
from the official website for Pi
Day.
- Listen to a pi song. My students love the Pi
Song. You can hear the first 100 or so digits sung during this song.
Pi, Pi, Mathematical
Pi is another song. This one is to the tune of the song American
Pie. It has a Flash movie accompanying it. My students love this one
too!
- Learn more about pi. Ask
Dr. Math - About Pi answers the questions: What is pi? Who first
used pi? How do you find its value? What is it for? How many digits
is it? Check out this
section devoted to questions from middle school students.
- Celebrate Pi Day. Pi
Day from Exploratium has helpful information to help you celebrate
Pi Day.
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