Curriculum fit: GCSE Physics and Combined Science (particle model of matter). US: middle and high school physical science (properties of matter).
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What Is It?
Density tells you how much mass is packed into a given volume. A steel block is denser than a wooden block of the same size, because steel has more mass per unit of volume.
An object floats in a fluid if it is less dense than the fluid, and sinks if it is more dense. Water has a density of about 1 g/cm³.
Key Formulas and Ideas
- Density ρ = mass ÷ volume (ρ = m/V).
- Units: g/cm³ or kg/m³. 1 g/cm³ = 1000 kg/m³.
- Volume of an irregular solid can be found by displacement of water.
Worked Examples
Calculate Density
A metal block has mass 240 g and volume 30 cm³. Find its density.
- ρ = m ÷ V.
- = 240 ÷ 30 = 8.
✓ Answer 8 g/cm³
Find the Mass
Wood has density 0.6 g/cm³. What is the mass of 50 cm³?
- m = ρ × V.
- = 0.6 × 50 = 30.
✓ Answer 30 g
Irregular Object
Describe how to measure the density of a small stone.
- Measure its mass on a balance.
- Put it in a measuring cylinder of water and note the rise in water level, which is its volume.
- Divide mass by volume.
✓ Answer Density = mass ÷ displaced volume
Common Mistakes to Avoid
- Mixing up the units of mass and volume.
- Dividing volume by mass.
- Forgetting to convert between g/cm³ and kg/m³.
- Reading the water level at the wrong point of the meniscus.
Practice Questions
Frequently Asked Questions
Why does ice float on water?
Ice is less dense than liquid water because water molecules are arranged more openly in ice.
How do I convert 2.7 g/cm³ to kg/m³?
Multiply by 1000: 2700 kg/m³.
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GCSEHigh SchoolSources and Review
Reviewed by StudyMorrow editorial review on 5 Nov 2026.