Density
Density is the mass of a substance per unit volume, showing how tightly its particles are packed.
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Density is the mass of a substance per unit volume, showing how tightly its particles are packed.
- Density equals mass divided by volume
- Water has a density of 1000 kg per cubic metre
- Less dense materials float on denser fluids
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Density?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Density. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Density in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Density explains how the physical world behaves, from sport and transport to electricity and medicine.
Density in detail
Density is the mass per unit volume of a substance: ρ = m/V, measured in kg/m³ or g/cm³. Water has a density of 1,000 kg/m³ (1 g/cm³), so objects with lower density float in it and those with higher density sink.
To find the density of a regular solid, measure its dimensions to get the volume and weigh it. For an irregular object, use displacement of water in a measuring cylinder. Density helps identify materials, explains why ships float and why hot air rises, and is key in engineering design.
How the interactive helps you understand Density
Watch the gas particle model in the interactive. Use any sliders or buttons it offers to change the values and see how the gas particle model responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Density.
Real-life uses and examples
- Predict what a ball, car or circuit will do with Density before you do the calculation.
- Explain everyday devices, such as brakes, lifts or chargers, using Density.
- Use Density to make sense of a practical and its results.
Common mistakes to avoid
- Mixing up Density with a related quantity that has different units.
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Density
What is Density?
Density is the mass of a substance per unit volume, showing how tightly its particles are packed.
What are the most important points about Density?
The main points are: Density equals mass divided by volume; Water has a density of 1000 kg per cubic metre; Less dense materials float on denser fluids.
Why is Density useful?
Understanding Density explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Density?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Density?
Related topics in Physics include Acceleration, Projectile Motion, Newton's Third Law.