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A United States Navy Aviation boatswain's mate tests the specific gravity of JP-5 fuel. Relative density, also called specific gravity, [1] [2] is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.
When converting oil density to specific gravity using the above definition, it is important to use the correct density of water, according to the standard conditions used when the measurement was made. The official density of water at 60 °F according to the 2008 edition of ASTM D1250 is 999.016 kg/m 3. [2] The 1980 value is 999.012 kg/m 3. [3]
To calculate the density of air as a function of altitude, one requires additional parameters. For the troposphere, the lowest part (~10 km) of the atmosphere, they are listed below, along with their values according to the International Standard Atmosphere , using for calculation the universal gas constant instead of the air specific constant:
The specific weight, also known as the unit weight (symbol γ, the Greek letter gamma), is a volume-specific quantity defined as the weight W divided by the volume V of a material: = / Equivalently, it may also be formulated as the product of density, ρ, and gravity acceleration, g: = Its unit of measurement in the International System of Units (SI) is newton per cubic metre (N/m 3), with ...
Buoyancy force = weight of object in empty space − weight of object immersed in fluid. The final result would be measured in Newtons. Air's density is very small compared to most solids and liquids. For this reason, the weight of an object in air is approximately the same as its true weight in a vacuum.
where stands for "submerged specific gravity", is the density of the object, and is the density of the fluid. Submerged specific gravity is equal to the specific gravity given by the ratio of the weight of the object to the weight of the fluid) minus one. That is, the object and fluid have the same density when the specific gravity equals one ...
Since API gravity is an inverse measure of a liquid's density relative to that of water, it can be calculated by first dividing the liquid's density by the density of water at a base temperature (usually 60 °F) to compute Specific Gravity (SG), then converting the Specific Gravity to Degrees API as follows: = =
As 0 °Bx is approached °P tend toward as much as 0.002 °P higher than the °Bx calculated for the same specific gravity. Disagreements of this order of magnitude can be expected as the NBS and the ASBC used slightly different values for the density of air and pure water in their calculations for converting to apparent specific gravity.