How is specific gravity defined?

Specific gravity is defined as the ratio of the density of a substance to the density of a reference substance, typically water for liquids. This measurement provides an understanding of how dense a material is relative to water, which has a defined density of 1 g/cm³ at 4°C. When the specific gravity is calculated, it helps in identifying the buoyancy characteristics of liquids—whether a substance will float or sink when placed in water.

For liquids, if the specific gravity is less than 1, the substance will float, and if it is greater than 1, the substance will sink. This concept is crucial in fields like chemistry, physics, and engineering, as it helps in characterizing materials and understanding their behavior in various environments.

The other potential definitions do not correctly capture the concept of specific gravity. For instance, comparing the weight of a substance to air does not relate specifically to the concept of specific gravity, which is density-based and typically involves water as the reference. The volume of a gas compared to that of a liquid and the rate at which a substance changes state are unrelated to the measurement of specific gravity, focusing instead on different physical properties of substances.