Volume vs Density
Volume and density are important physical properties of matter. They are widely used in chemistry and fluid dynamics. Mass of an object can be derived if both these properties are provided.
Volume measures the amount of three dimensional space occupied by an object. SI unit for measuring volume is ‘cubic meter’. However, ‘litre’, which is equal to a thousandth of a cubic meter (or a cubic decimeter) is the most popular measuring unit for volume. Ounce, pint and gallon are the units in imperial system for volume. One millilitre is equal to a cubic centimeter. Volume has dimensions of L3 (length x length x length).
Unlike the mass, volume changes according to the external conditions. As an example, volume of a sample of gas depends on the air pressure. Volume of a solid can be changed when it is melted.
There are mathematical expressions to calculate the volume of general shapes (length x height x width for a cuboid, and 4/3 x πr3 for a sphere). For objects with complicated shapes, measuring the amount of displaced liquid is the best option.
Density is a physical property of matter, which is a measure of the amount of matter available in a unit volume. Density of an object doesn’t change with the size of the sample, and hence, called an intensive property. Density is the ratio between mass to volume, and therefore, has the physical dimensions of ML-3. Measuring unit for density may be kilograms per cubic meter (kgm-3) or grams per millilitre (g/ml).
When a solid object is put in to a liquid it will float, if the solid has a lesser density than liquid. This is the reason for ice floating on water. If two liquids (which do not mix with each other) with different densities are put together, the liquid with a lesser density floats on the liquid with the higher density.
In some specific applications, density is defined as weight/volume. This is known as specific weight, and in this case, units should be Newtons per cubic meter.
Difference between volume and density
1. Volume is measured in cubic meters, whereas density is measured in kilograms per cubic meter.
2. Density is inversely proportional to volume if the mass is constant. That means density decreases when the volume is increased, while keeping the mass constant. This is why the density of an object may get decreased when it is expanded.
3. Density is an intensive property, whereas volume is an extensive property.
4. Density is the mass calculated by keeping the volume constant (that is one unit).