A TedEd by Reynaldo Lopez
If you were to measure the parts of a circle, how would you do it? The radius and diameter can simply be measured with a ruler, and the circumference would be a bit more complicated, perhaps requiring a tape measure. But there is actually a very important relationship between the circumference and diameter. The ratio of the two is what is known as pi. Although it is unknown when this relation was first discovered, we can see evidence of it going back 4,000 years. It can be found in ancient Greek, Babylonian, Chinese, and Indian texts, and is even believed to have been used in building the pyramids. Mathematicians estimated it by inscribing polygons in circles, but we will never be able to get an exact value for it. This is because pi is an irrational number, or cannot be expressed as the ratio of two whole numbers. So in decimal form, pi is an endless series of digits starting with 3.14159. For everyday usage, we write it as π instead of an infinite string of numbers, and there are even world records for memorizing the most numbers. Pi is used in all calculations involving circles, and it can also be used for curves and oscillations like clocks and music. In statistics, it is used in the calculation of a normal distribution curve, and it has been used in physics for the Hadron Collider and proof of the wave-particle duality of light. In fact, it has even been used to calculate the total density of our universe!
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