# Gravity

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Gravity, abbreviated as g, also called gravitation, is a force pulling togeather all matter.  Everything that has mass has a gavitational pull that is exerted on one another.  The larger the mass, the stronger the gravitational pull is exerted, this includes all matter.

## API Gravity

The oil industry uses the API Gravity or Gravity scale. If a fluids API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. API gravity is thus a measure of the relative density of a petroleum liquid and the density of water, but it is used to compare the relative densities of petroleum liquids.

The relationship between API Gravity and specific gravity is as follows:

$$\large{ API_{gravity} = \frac{141.5}{SG} - 131.5 }$$

So using the above equation, an oil with a specific gravity of 1.0 would have an API Gravity of (141.5 1.0) -131.5 = 10.0 degrees API.

## Gravitational Mass

Gravitational mass is measured by comparing the force of gravity of an unknown mass to the force of gravity of a known mass.  Acceleration of gravitational mass will always be the same on each object no matter where you are on the planet.

## Universal Gravitational Constant

The universal gravitational constant, abbreviated as G, is the proportionality constant used in Newton's Law of Universal Gravitation.  This constant is very difficult to measure with any high accuracy.

$$\large{ G = 6.67384 \; \left( 10^{-11} \; m^3 \; kg^{-1} \; s^{-2} \right) \; = \; 6.67384 \; \left( 10^{-11} \; Nm^2 \; kg^{-2} \right) }$$