# What Does Pi Have To Do With Gravity?

The relationship between pi (π) and gravity is an interesting one, although not a direct one. Pi is a mathematical constant with a seemingly endless string of decimal places, approximately equal to 3.14159, and it pops up in various calculations involving circles, spheres, and other curved shapes. Gravity, on the other hand, is the fundamental force that attracts any two objects with mass towards each other.

So, where does the connection come in?

1. Early Definition of the Meter:

Historically, the meter, the unit of length in the metric system, was defined as one ten-millionth of the Earth’s meridian. Imagine swinging a pendulum with a length of exactly one meter at Earth’s equator. In a small-angle approximation, the period of its swing, the time it takes to complete one full cycle back and forth, can be calculated using the following formula:

``````T = 2π * √(L / g)
``````

where:

• T is the period of the swing in seconds
• π is the mathematical constant pi
• L is the length of the pendulum in meters (in this case, 1)
• g is the acceleration due to gravity on Earth (approximately 9.81 m/s²)

Solving for g, we get:

``````g = 4π² * (L / T²)
``````

Interestingly, if we use the original definition of the meter (one ten-millionth of the Earth’s meridian) and the period of a pendulum with that length swinging at Earth’s equator, the calculated value of g would be very close to 9.81 m/s², the actual acceleration due to gravity on Earth. This coincidence led some early scientists to believe that there might be a fundamental connection between pi and gravity.

2. Circular Orbits and Pi:

Another connection between pi and gravity can be seen in the motion of celestial bodies. Planets and moons orbit stars and planets, respectively, in elliptical paths. While ellipses aren’t perfect circles, for many orbits, they are close enough that we can approximate them as circles. In this case, Kepler’s laws of planetary motion tell us that the ratio of a celestial body’s orbital period (T) to the square root of its average orbital radius (r) is a constant for all bodies orbiting the same central object. This constant is:

``````√(4π² / GM)
``````

where:

• G is the gravitational constant
• M is the mass of the central object

This equation again shows pi appearing in the context of orbital motion and gravity.

3. No Direct Relationship:

However, it’s important to remember that these connections are coincidental. Pi is a fundamental mathematical constant that appears in countless calculations involving circles and spheres, and gravity is a fundamental force of nature. There’s no underlying physical reason why pi should be directly related to the strength of gravity.

The historical definition of the meter and the approximation of planetary orbits as circles led to these interesting coincidences, but they don’t imply any deep connection between the two concepts. Pi and gravity are independent entities that play different roles in our understanding of the universe.

So, while there are some interesting ways in which pi shows up in calculations related to gravity, it’s crucial to remember that they are separate concepts with no direct relationship. Pi’s role is primarily mathematical, while gravity governs the interactions between massive objects.