The number Pi (written π) is probably the most famous number in all mathematics.
It is such a common thing. It is how many times the perimeter of a circle is bigger than its diameter.
This turns out not to be a whole number. In fact, it is a number that has no ending. You can get close, but you can never find it exactly, not even with a supercomputer.
For many purposes it is easy to remember as the fraction 22/7 or in decimal form 3.14
Ancient civilisations tried to work out this number because they, like us, worked with circles.
1. Take a long piece of string. Get a soup bowl and place it face down on a table. Wrap the string around the edge of the bowl where it meets the table. Use scissors to cut the string off exactly where it overlaps.
This is the circumference (perimeter).
2. Turn the bowl up the other way. Stretch a piece of string across its diameter. Cut it off to length.
This is the diameter.
3. Measure the length of the diameter string using a ruler.
4. Measure the length of the cicumference string using a ruler.
5. Divide the circumference by the diameter either using long division
(we have a book on that here) or by using a calculator.
6. If you use a calculator, look at the result you get. Compare it with the result that mathematicians get, which is 3.14159 (approximately). Why do you think your result may be slightly different? Think of how accurately you can measure using a ruler, the stretchiness of the string you used, the accuracy of cutting it to length, and anything else that might have affected your measurement.
7. Use a new piece of string and do the experiment again. Do you get the same result? If you repeated it several time and took an average of your results, do you think the result you get would be closer to the real value?
