Density = Mass / Volume

Density = Mass / Volume

Understanding Density

• Density is a measure of the amount of mass in a given volume of a substance.
• The formula for calculating density is Density = Mass / Volume. Here, mass is measured in kilogrammes (kg) and volume is measured in cubic metres (m³), so density is measured in kilogrammes per cubic metre (kg/m³).
• When the mass of an object is dense, it means that the particles are closely packed.

Practical Applications of Density

• Buoyancy: Objects that are less dense than the fluid they are in will float. This is due to the buoyant force being greater than the object’s weight.
• Layering: In a mixture of liquids, the liquid with lower density will float on top of a liquid with higher density.

Calculating Density

• Mass is measured using a balance. If the object is irregularly shaped, it can be weighed by first weighing an empty container, then the container with the object, and subtracting the two weights.
• Volume can be calculated by measuring length, width and height for a regularly shaped object (and using the formula: volume = length x width x height). For irregularly shaped objects, volume can be measured by displacement of water.

Importance of Units

• Always ensure you use correct units when calculating density. The SI unit for density is kg/m³, however, g/cm³ is often used for solids, and g/ml for liquids.
• When using the density formula, the units of your final answer will always be the type of mass unit divided by the type of volume unit. For instance, if the mass was given in grammes and the volume in cubic centimetres, the density would be in grammes per cubic centimetre (g/cm³).