# A block of wood floats on water. A block of iron of the same volume sinks in water. Explain why the block of wood floats whilst the block of iron sinks, using the concept of density.

> Cambridge International IGCSE Physics (0625) — 1.4 Density · Explain · 4 marks

> Water has a density of 1000 kg/m³. Wood has a density of approximately 600 kg/m³. Iron has a density of approximately 7900 kg/m³.

## Mark scheme (4 marks)

1. Density is mass per unit volume
2. Wood has a lower density than water / wood's density is less than 1000 kg/m³
3. Iron has a higher density than water / iron's density is greater than 1000 kg/m³
4. An object floats if its density is less than the fluid it is placed in, and sinks if its density is greater than the fluid

## Key terms

- [density](https://www.gradenine.co.uk/glossary/density)
- [volume](https://www.gradenine.co.uk/glossary/volume)

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-block-of-wood-floats-on-54c8d078) · Published by Druglandscape Ltd.