AQA GCSE FOUNDATION PHYSICS - Density and States of Matter

AQA GCSE Foundation Physics: Density and States of Matter

What is Density?

Density is a measure of how much mass is contained in a given volume. It tells us how tightly packed the particles are within a substance. The formula for density is:

Density = Mass / Volume

• Mass: The amount of matter in an object (measured in kilograms, kg)
• Volume: The amount of space an object occupies (measured in cubic meters, m³)
• Density: Measured in kilograms per cubic meter (kg/m³)

Density Across States of Matter

The state of matter (solid, liquid, or gas) affects the density of a substance. Here's why:

• Solids: Particles in solids are tightly packed and vibrate in fixed positions. This gives solids a high density.
• Liquids: Particles in liquids are closer together than in gases but can move around more freely. This gives liquids a lower density than solids.
• Gases: Particles in gases are far apart and move randomly. This gives gases a very low density.

Examples

• Example 1: A block of iron has a mass of 5 kg and a volume of 0.001 m³. Its density is:

Density = Mass / Volume = 5 kg / 0.001 m³ = 5000 kg/m³ 

• Example 2: Water has a density of 1000 kg/m³. This means that 1 cubic meter of water has a mass of 1000 kg.

Key Points

• Density is a physical property of a substance, meaning it doesn't change based on the amount of substance present.
• Density is a useful property for identifying substances. For example, gold is much denser than wood, so we can use density to distinguish between the two.
• Temperature can affect density. Generally, substances become less dense as they heat up (except for water between 0°C and 4°C).