What is the definition of density in physics?

Density in physics is defined as the mass of an object divided by its volume.

In more detail, density is a measure of how much mass is contained in a given volume. It is a fundamental concept in physics and is particularly important in understanding the properties of matter. The standard unit of density in the International System of Units (SI) is the kilogram per cubic metre (kg/m³), although it can also be expressed in other units such as grams per cubic centimetre (g/cm³).

To calculate the density of an object, you need to know both its mass and its volume. The mass is usually measured with a balance or scale, while the volume can be determined in various ways depending on the shape and size of the object. For example, the volume of a regular solid can be calculated using geometric formulas, while the volume of an irregular solid or a liquid can be measured using displacement methods.

The concept of density is used in many areas of physics and engineering, including fluid dynamics, material science, and thermodynamics. It can help to explain why some objects float while others sink, why different materials have different strengths and other physical properties, and how heat and sound are transmitted through different substances.

In addition, the density of a substance can change under different conditions. For instance, most substances expand when heated, which means their volume increases and their density decreases. Similarly, pressure can also affect the density of gases and, to a lesser extent, liquids. Understanding these changes in density is crucial for many practical applications, such as designing engines, predicting weather patterns, and developing new materials.