What does specific gravity compare?

Specific gravity is a dimensionless quantity that indicates the ratio of the density of a substance to the density of a reference substance, which is typically water for liquids and solids. When we say that specific gravity compares the weight of a substance to the weight of an equal volume of water, we are essentially stating how heavy a substance is relative to water, facilitating comparisons of materials in terms of buoyancy and other properties.

This measure is particularly useful in various applications, such as determining whether a substance will float or sink in water and understanding its concentration in solutions. For example, if a substance has a specific gravity greater than 1, it will sink in water; if it is less than 1, it will float.

The other options focus on different comparisons that do not align with the definition of specific gravity. For instance, density relates to various substances, while specific gravity is specifically a volumetric comparison to water. Understanding the fundamental concept of specific gravity is critical in fields like refrigeration, where the properties of materials can greatly impact system efficiency and functionality.