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What is a solid?
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Quick answer
A solid is a state of matter with a fixed shape and volume. Its particles are packed closely together in a regular arrangement and can only vibrate in place, which is why a solid holds its form instead of flowing or spreading out.
Key things to understand
- A solid keeps both its shape and its size — it doesn't flow or expand to fill a container.
- Its particles are tightly packed and locked in position, vibrating but not moving past each other.
- Because the particles are so close, solids are usually very hard to compress.
- Heating a solid enough makes its particles vibrate so much that it melts into a liquid.
- Solids can be crystalline (orderly, like salt) or amorphous (jumbled, like glass).
People also ask
Why does a solid keep its shape?
Its particles are held tightly in fixed positions by strong forces, so they can only vibrate in place — they can't slide past one another to let the solid flow.
What happens when a solid is heated?
The particles gain energy and vibrate harder. Heat it enough and they break free of their fixed positions, and the solid melts into a liquid.
Are all solids hard?
No. Rubber and wax are solids too. What makes something a solid is its fixed shape and volume, not how hard it feels.