density

Everyday

1. Density is how much mass is packed into a certain amount of space; dense things are heavy for their size. tree →
2. Density is also how crowded or close together things are in an area (population density). tree →

In the lessons

In science, density explains why things float or sink: wood is less dense than water so it floats, a stone is denser so it sinks; oil floats on water. In maths and geography, population density is the number of people per square kilometre, found by dividing people by area. Phrases: high density, low density, population density, density of water.

Examples

• Lead has a very high density. tree →
• Ice floats because its density is lower than water's. tree →
• Oil has a lower density than water, so it floats on top. tree →
• Cities have a high population density. tree →
• The density of trees in the jungle makes it dark. tree →
• We compared the density of different liquids in a jar. tree →

Note

Mostly uncountable; countable when comparing (different densities). Adjective: dense. In maths: density = mass ÷ volume; population density = number of people ÷ area. Trap: a big object is not always dense; a large ball of cotton wool has low density.