What is the definition of density?

Density is the measure of mass per unit volume of a substance.

In more detail, density is a fundamental property of matter that helps us understand how much mass is packed into a given volume. It is calculated using the formula:

\[ \text{Density} = \frac{\text{Mass}}{\text{Volume}} \]

The units commonly used for density are kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³). For example, water has a density of approximately 1 g/cm³, which means that 1 cubic centimetre of water has a mass of 1 gram.

Understanding density is crucial in various scientific and practical applications. For instance, it helps us determine whether an object will float or sink in a fluid. Objects with a density lower than the fluid will float, while those with a higher density will sink. This principle is why ice floats on water and why ships, despite being made of dense materials like steel, can float because their overall density, including the air inside, is less than that of water.

In GCSE Physics, you might encounter problems where you need to calculate the density of an object by measuring its mass and volume. For example, if you have a metal block with a mass of 200 grams and a volume of 50 cubic centimetres, you can find its density by dividing the mass by the volume:

\[ \text{Density} = \frac{200 \text{ g}}{50 \text{ cm}^3} = 4 \text{ g/cm}^3 \]

This means the metal block has a density of 4 grams per cubic centimetre.

Density also plays a role in understanding the behaviour of gases and liquids under different conditions, such as changes in temperature and pressure. By studying density, we gain insights into the composition and properties of different materials, which is essential in fields ranging from engineering to environmental science.