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Happy Pi Day! What the number is actually used for

  • Happy Pi Day! What the number is actually used for

    Mystical, magical pi has captured the imaginations of mathematicians for almost 4,000 years. An irrational number that stretches to infinity and beyond, pi is more than just an esoteric mathematical puzzle—it’s a reassuring constant that regulates the patterns and rhythms of the natural world around us, as well as within us.

    Merriam Webster defines pi as both the symbol (π) representing the ratio of the circumference of a circle to its diameter, as well as the ratio itself—a transcendental number generally rounded to 3.14159265. The Babylonians and the ancient Egyptians were both conscious of the concept of pi in its most basic expression. Around 250 B.C., the Greek mathematician Archimedes of Syracuse extended pi to 3.141. In the early 1990s, the Chudnovsky brothers, using a computer cobbled together in their cramped Manhattan apartment, calculated pi to more than 2 billion digits. More recently, supercomputers have pushed pi past the 22 trillion digit mark.

    In honor of international Pi Day—the 14th day of the third month of the calendar year—Stacker has isolated 20 of the most accessible uses of pi in everyday lives. So whether you choose to celebrate with cherry, pizza, or chicken pot pie, rest assured: On Pi Day you can have your pi and eat it, too.

    You may also like: Scientific breakthroughs from the year you were born

  • Birth of pi

    Pi is used to determine the area of a circle. Pi's importance, however, extends far beyond that simple calculation. It stars in a number of other, larger mathematical equations, including Euler's identity and the Fourier transform, both of which have had a tremendous impact on the fields of science, technology, and engineering. The snappy symbol π, derived from the Greek alphabet, was introduced by Welsh mathematician William Jones in the early 18th century.

  • Piping hot pi

    Pi is an essential element of the Fourier transform, developed in 1822 by French mathematician Jean-Baptiste-Joseph Fourier to measure the movement of heat waves. The equation continues to inform the design of modern heating systems. Scientists at the University of Maryland recently created a self-powered thermo-regulation fabric, which instinctively warms the body, vetting the material's effectiveness with a Fourier-transform IR spectrometer.

  • Pi and DNA

    Pi can be used to measure one of the most basic components of human life—DNA. The ladder-like structure of DNA contains a mind-boggling amount of genetic information, typically measuring 1.8 meters long. Amazingly, this string manages to wrap itself into a tiny, 10-micron sphere—approximately 1.8 pi of its original length.

  • Population proportion

    What proportion of the American population has brown eyes? Owns their home? Can speak a foreign language? All of these questions can be answered with the help of the Greek letter π (pi), commonly used by statisticians when calculating population proportions.

  • Rolling on a river

    In 1926, Albert Einstein noted that rivers often travel in loops, which are similar to circles. As with all things that curve or bend, pi appears to inform the length of meandering rivers, known as sinuosity. In 1996, Hans-Henrik Stolum built on Einstein's observations, determining that the sinuosity of the average river trends toward 3.14, or pi.

  • Pi and the Pyramids

    In 1859, British writer and theorist John Taylor realized that the perimeter of the Great Pyramid at Giza, when divided by its height, equals 2pi. Like their ancient Egyptian predecessors, modern architects and engineers also rely on pi when calculating curved elements, such as pillars and pipes.

  • Siesmic pi

    Vibrations—including those created by earthquakes—travel in waves, and can, therefore, be measured by the Fourier transform. Engineers and architects can consult data gleaned from Fourier Transform infrared microspectroscopy to design buildings capable of withstanding the potentially disastrous effects of shifting tectonic plates.

  • Electric pi

    The drudgery associated with household chores is decidedly less onerous thanks to modern electrical appliances—all of which owe their existence to pi. Pi is critical for the computation of electrical currents and their accompanying wave patterns. The larger the wave pattern, the bigger the wire needed to contain the power coursing through it.

  • Pi plays ball

    Whether you're knocking it out of the park, dunking it through a hoop, or slamming it cross court, a ball is essentially a simple sphere. As with the manufacture of any spherical object, its surface area, which determines the amount and cost of the materials necessary for production, is calculated using pi.

  • Computing pi

    It took a supercomputer to calculate pi to a jaw-dropping 22 trillion digits, yet without pi, which is used to calculate the area of microchips, computers never would have existed. Engineers also rely on pi to determine the size and shape of a computer, as well as necessary air flow.