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Density

Density is the mass per unit volume. It can be measured in several ways.

The most accurate way to calculate the density of any solid, liquid or gas is to divide its mass in kilograms by its volume (length × width × height) in cubic metres.

Density can be found using the equation:

Equation: Density = frac{mass}{volume}

Equation: rho = frac{m}{v}

The unit for density is kg/m3. The density of water is approximately 1000 kg/m3 and the density of air is approximately 1.2 kg/m3.

If solid objects are placed in water and they sink, they have a density greater than water (1000 kg/m3). The reverse is also true.

If several liquids that don’t mix (immiscible) are placed in the same container, the least dense one will rise to the top and the densest one will sink to the bottom. This is also true of gases, but they are often harder to see because gases tend to mix with each other very easily.

Take a look at this practical demonstration of the relative densities of liquids:

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Not all objects have regular volumes that are easy to measure. A ‘eureka can’ can be used in these cases.

Eureka can filled with water to just below overflow hole. Object lowered into can and displaces own volume of water. Water passes through overflow, down spout and collected in measuring cylinder.

Calculating volume of a solid using a Eureka can

A eureka can is a container large enough to hold the object with a spout positioned near the top. The can is filled to the top with water and the object placed in it. The volume of the object is equal to the volume of the water that is forced through the spout.

Eureka cans are named after a scientist called Archimedes who first recorded this idea. They are sometimes also called displacement vessels.

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Glossary
  1. condense Condensation is a change of state in which gas becomes liquid by cooling.