Defining Specific Gravity
Specific gravity is a dimensionless quantity that represents the ratio of the density of a substance to the density of a reference substance. For liquids and solids, the reference substance is almost always water at a specific temperature (usually 4°C, where its density is 1 g/cm³). For gases, the reference substance is often air or hydrogen.
Key Principles and Characteristics
Because specific gravity is a ratio of two densities, it has no units. It indicates how much denser or lighter a substance is compared to the reference. A specific gravity greater than 1 means the substance is denser than water and will sink, while a specific gravity less than 1 means it's less dense and will float. This property is crucial for understanding buoyancy.
A Practical Example
Consider a substance with a density of 0.8 g/cm³. Compared to water (density 1 g/cm³), its specific gravity would be 0.8 / 1 = 0.8. This tells us the substance is 0.8 times as dense as water and would float. Conversely, a substance with a density of 2.5 g/cm³ has a specific gravity of 2.5, indicating it is 2.5 times denser than water and would sink.
Importance and Applications
Specific gravity is widely used in various fields. In geology, it helps identify minerals; in engineering, it's vital for designing structures that interact with fluids, such as ships or pipelines. Clinical laboratories use it to analyze urine samples, and in automotive contexts, it's used to check the charge level of a car battery by measuring the specific gravity of the electrolyte.