Density is the amount of mass in a given volume of matter. Relative density, or specific gravity, compares the density of a material to a standard, such as water. Mass is the amount of matter in a substance, while weight can change with gravity. Density is calculated by dividing mass by volume. Relative density is a ratio and does not require units. Water is commonly used as a standard for relative density calculations. Materials can have a specific gravity greater or less than 1.0, depending on their density compared to water.
Density is a measure of how much mass is present in a given volume of matter. Relative density is the comparison between the density of a material and the density of a particular standard, such as water, at a given temperature or pressure. Relative density is also known as specific gravity.
Most commonly, density is calculated in metric units. A widely used option is to indicate the density in grams per cubic centimeter (g/cm3). A gram is a measure of mass and a cubic centimeter is a measure of volume.
Mass is the amount of matter in a substance and the inertness of that substance. It is different from weight because weight can change with changes in gravity on the object. An object is heavier on Earth than on the moon, for example, because there is less gravity on the moon. However, the mass remains the same in both cases.
When calculating the density of a substance, the mass and volume must be known. The equation needed is density = mass/volume. For example, 1 gram of water occupies 1 cubic centimeter of volume. A cubic centimeter is also known as a milliliter when referring to liquids, so the equation for the density of water would be 1g/1ml. The density is therefore equal to 1 g/ml, which can also be expressed as 1 g/cc or 1 g/cm3.
Density measurements require units of mass and volume to be included in the response. Relative density, on the other hand, is simply a comparison of densities between two substances as a ratio, so units are unnecessary. For example, the relative density of one water sample relative to another water sample is 1.0 g/ml : 1.0 g/ml, and since the units on either side cancel each other out, the final answer is simply 1.0 .
Water is typically used as the standard for relative density calculations for solids and liquids. This is useful because the substance is being compared to a substance that has a simple density of 1 g/ml. For gases, a standard of a specific gas could be used. The density of materials can vary with ambient pressure and temperature, so the standard density is limited to a particular temperature or, for gases, a particular pressure.
Using water as the standard, substances heavier than water, such as gold, produce specific gravity values greater than 1.0. Gold has a relative density of 19.30 and common table salt a relative density of 2.16. Less dense materials have a value of less than 1.0, such as ammonia at 0.8974 or pine sticks at around 0.50.
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