Specific Gravity Formula |
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\( SG \;=\; \dfrac{ \rho_s }{ \rho_r }\) (Specific Gravity) \( \rho_s \;=\; SG \cdot \rho_w \) \( \rho_w \;=\; \dfrac{ \rho_s }{ SG }\) |
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| Symbol | English | Metric |
| \( SG \) = Material Specific Gravity (water = 1) | \(dimensionless\) | \(dimensionless\) |
| \( \rho_s \) (Greek symbol rho) = Substance Density | \(lb \;/\; ft^3\) | \(kg \;/\; m^3\) |
| \( \rho_w \) (Greek symbol rho) = Reference Substance Density | \(lb \;/\; ft^3\) | \(kg \;/\; m^3\) |
Specific gravity, abbreviated as SG, a dimensionless number, often used interchangeably with relative density, it quantifies how dense a substance is in comparison to a reference material. It is calculated by dividing the density of the substance by the density of a standard reference substance, typically water at 4°C for liquids and solids, or dry air for gases. Since it is a ratio of two densities with the same units, specific gravity is a unitless value. This measurement is particularly useful because it directly indicates whether a substance will float or sink in the reference fluid, a specific gravity less than 1 means it will float (less dense), greater than 1 means it will sink (denser), and exactly 1 means it has the same density as the reference. Specific gravity is widely applied in various fields, including chemistry, engineering, and geology, to identify materials, determine concentrations of solutions, and assess buoyancy.
For example, in the context of minerals and ores, specific gravity is often used to determine the mineral composition and to assess the concentration of valuable components. In the petroleum industry, specific gravity is used to classify and measure the density of crude oil and other hydrocarbon liquids. It's important to note that specific gravity is temperature dependent because the density of both the substance and water can vary with temperature. Therefore, when specific gravity is specified, the temperature at which it is measured should be indicated.
