Knowing the above facts allows us to figure things
like,
how fast will that gocart travel?
For example: If you had a gocart with an engine capable
of 3000 R.P.M's (revolutions per minute) with a drive train
reduction of 2 to 1, with 10 inch diameter tires, then
3000 divided by 2 = 1500
(revolutions per minute after drive train reduction)
Pi or 3.14159 times 10 = 31.4159
(inches traveled in one tire revolution)
1500 times 31.4159 = 47123.85
(Inches traveled in one minute)
47123.85 divided by 12 = 3926.9875
( feet traveled in one minute)
3926.9875 times 60 = 235619.25
(feet traveled in one hour)
235619.25 divided by 5280 = 44.6248
(miles per hour).

This is one example of using the weird sounding mathematical
figure, Pi, to provide an answer to a simple question.
Also:
Pi times (the radius times the radius) of a circle
produces the area inside a circle.
For example, a ten inch diameter circle has an area of:
5 times 5 = 25
(radius times radius)
25 times Pi or 3.14159 = 78.53975 inches
