Density (AQA GCSE Physics Combined Science): Revision Notes

📚 Revision Notes
Revision NotesModel AnswersQuizzesFlashcards

Density

What is density?

Density tells us how much matter is packed into a space. It measures the amount of matter that fits into each unit of volume.

Think of it like this - imagine you have two boxes the same size. One is packed full of heavy metal balls, the other has just a few light plastic balls. The box with metal balls has a higher density because more matter is squeezed into the same space.

The density formula

The formula for density is simple:

density=massvolume\text{density} = \frac{\text{mass}}{\text{volume}}

You can also write this as: ρ=mV\rho = \frac{m}{V}

Where:

  • ρ\rho (rho) = density
  • mm = mass
  • VV = volume
infoNote

You can rearrange this formula to find mass or volume:

  • mass = density × volume → m=ρ×Vm = \rho \times V
  • volume = mass ÷ density → V=mρV = \frac{m}{\rho}

Units for density

The main unit for density is kg/m³ (kilogrammes per cubic metre).

You might also see g/cm³ (grammes per cubic centimetre).

chatImportant

Always check your units match! If mass is in kg and volume is in m³, then density will be in kg/m³.

Density in different states of matter

The arrangement of particles affects density:

Solids

  • Particles are tightly packed together
  • High number of particles in each unit of volume
  • Highest density

Liquids

  • Particles are less tightly packed than solids
  • Fewer particles in each unit of volume compared to solids
  • Medium density

Gases

  • Particles are spread far apart
  • Very few particles in each unit of volume
  • Lowest density

Key calculation tips

infoNote

When doing density calculations:

  1. Check you're using the right equation for what you want to find
  2. Make sure units match - kg with m³, or g with cm³
  3. Show your working step by step
lightbulbExample

Worked Example: Finding Density

A material has a mass of 84 kg and volume of 0.075 m³. Find its density.

Step 1: Write the formula density=massvolume\text{density} = \frac{\text{mass}}{\text{volume}}

Step 2: Substitute the values density=84 kg0.075 m3\text{density} = \frac{84 \text{ kg}}{0.075 \text{ m}^3}

Step 3: Calculate density=1120 kg/m3\text{density} = 1120 \text{ kg/m}^3

Important facts about density

chatImportant

Key Properties of Density:

  • Changing volume changes mass too - if you double the volume of a material, you double its mass, so density stays the same
  • Density doesn't change when you have more or less of the same material
  • Different materials have different densities - this is what makes some things float and others sink
bookmarkSummary

Key Points to Remember:

  • Density measures how much matter fits in a unit of volume
  • Formula: density=massvolume\text{density} = \frac{\text{mass}}{\text{volume}}
  • Units: kg/m³ or g/cm³
  • Solids have the highest density, gases have the lowest density
  • Always check your units match in calculations

Explore AQA GCSE Physics Combined Science Model Answers by Topics

Changes of State & the Particle Model

Internal Energy & Energy Transfers

Particle Model & Pressure

Explore AQA GCSE Physics Combined Science Quizzes by Topics

Changes of State & the Particle Model

Internal Energy & Energy Transfers

Particle Model & Pressure

Explore AQA GCSE Physics Combined Science Flashcards by Topics

Changes of State & the Particle Model

Internal Energy & Energy Transfers

Particle Model & Pressure

Join 100,000+ GCSE students studying Revision Notes with us.

Select your subjects, and get access to A+ resources today.