The relative density of a substance is commonly referred to as what?

The term that is commonly used to refer to the relative density of a substance is specific gravity. Specific gravity is a dimensionless quantity which is defined as the ratio of the density of a substance to the density of a reference substance, typically water for liquids or solids, and air for gases. This measurement allows for the comparison of the density of various substances without needing to consider their specific units of measurement.

Specific gravity is particularly useful in various fields, including esthetics, where it may help to understand how different formulations behave in relation to each other, especially when considering the application and mixing of products. The concept helps professionals determine whether a substance will float or sink in water, which can be critical in the formulation and application of beauty products and treatments.

The other terms listed do not accurately describe the concept of relative density. Density index, specific weight, and relative weight are not commonly used terms in scientific contexts to refer to relative density and could lead to confusion in practice. Specific gravity remains the standard terminology in both scientific and industry applications.