* Specific Gravity is a ratio: Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water at 4°C). This is useful for comparing the density of solids and liquids.
* Air is a gas: Gases are compressible and their density changes significantly with temperature and pressure. This means the density of air is not constant and varies greatly, making it impractical to define a specific gravity for it.
Instead of specific gravity, we use air density which is:
* Measured in kg/m³: Air density is dependent on temperature, pressure, and humidity.
* Standard values: At standard atmospheric pressure (101.325 kPa) and 15°C (59°F), dry air has a density of approximately 1.225 kg/m³.
Therefore, it's more accurate to talk about the density of air under specific conditions rather than its specific gravity.
