Solid, Liquid, Gas: The Three States of Matter

Pick up a pencil. Pour a glass of water. Take a deep breath of air. All three of those things are real, but they feel very different. Why? The pencil stays in one shape. The water flows and takes the shape of the glass. The air you breathe is invisible! Scientists noticed this pattern too — and it led to one of the most useful ideas in all of science.

All the stuff in the universe is called matter. Scientists have found that matter exists in three main states: solid, liquid, and gas. **Solids** keep their own shape. You do not need a container to hold a solid — a rock, an apple, or a book all stay the same shape on their own. Inside a solid, the tiny particles (too small to see) are packed tightly together and can only vibrate in place. **Liquids** do not keep a fixed shape. A liquid flows and fills the bottom of whatever container you put it in. Water in a round bowl looks round; water in a tall bottle looks tall. The particles in a liquid are still close together, but they can slide past each other — that is why liquids pour. **Gases** spread out to fill any space they are in. You cannot usually see a gas, and it has no fixed shape or size. The particles in a gas move very fast and are far apart from each other. The air around you is a mixture of gases. **A real-world example you can see at home:** Boil a kettle of water. The water inside is a liquid. The steam that floats away is water that has turned into a gas. If you put an ice cube in a glass, that ice is the same water in a solid state. The same substance — water — can exist as a solid (ice), a liquid (water), and a gas (steam). This shows that the state of matter depends on temperature.