Anything that has mass and takes up space is called matter — your book, the water in a glass, even the air around you. Matter is made of tiny particles that are constantly moving, have spaces between them, and attract each other.
The three states of matter
- ✓ Solid: particles are packed tightly with strong attraction, so a solid has a fixed shape and volume.
- ✓ Liquid: particles are a little farther apart and can move around, so a liquid takes the shape of its container but keeps a fixed volume.
- ✓ Gas: particles are far apart and move freely and fast, so a gas has neither a fixed shape nor a fixed volume.
Changing states
Matter changes state when we change its temperature or pressure. Heating gives particles more energy so they break free; cooling does the reverse.
- ✓ Melting: solid → liquid (at the melting point). Freezing: liquid → solid.
- ✓ Boiling/vaporisation: liquid → gas (at the boiling point). Condensation: gas → liquid.
- ✓ Sublimation: solid → gas directly, e.g. camphor.
Two useful terms: latent heat is the hidden heat absorbed or released during a change of state without the temperature changing, and temperature in the lab is often measured in kelvin (0 °C = 273.15 K).
Evaporation
Evaporation is a liquid slowly becoming a gas below its boiling point, at the surface only. It speeds up with higher temperature, more surface area, lower humidity and more wind. Because evaporation absorbs heat from its surroundings, it causes cooling — which is why sweating cools us and water stays cool in an earthen pot (matka).
Want this taught aloud in your language?
The particle idea sticks best when it's explained with everyday examples and a quick check of understanding. Upload this NCERT chapter to Tutorfic and it will teach it aloud in your child's language, then quiz them on states and changes of state with the reasoning behind each answer. It's one of all the Class 9 subjects Tutorfic teaches.