States of Matter

Ice, water, steam — same substance, three completely different behaviours. The difference isn’t in the molecules themselves (they’re all H₂O) but in how the particles are arranged and how fast they’re moving. Turn up the temperature and you’re really just giving the particles more energy.

The three familiar states

• Solid — particles packed in a fixed, orderly arrangement. They vibrate in place but can’t move past one another, so a solid holds its shape.
• Liquid — particles still touching but no longer locked in place. They slide around, so a liquid flows and takes the shape of its container while keeping a fixed volume.
• Gas — particles flung far apart, moving fast in every direction. A gas spreads to fill whatever space it’s in.

Phase changes: crossing the thresholds

Add enough energy and particles overcome the attractions pinning them together:

• Melting — solid → liquid (the lattice breaks apart).
• Boiling / evaporation — liquid → gas (particles escape into the air).
• Run it backwards by cooling: condensing (gas → liquid) and freezing (liquid → solid).

Feel it with the slider

Drag the temperature slider and watch the particles respond. Cold: a tidy, vibrating lattice. Warmer: the order breaks down and they start to flow. Hot: they fly apart and bounce off the walls. Notice there’s no sharp “click” — the change is a matter of how much energy the particles have.

Check yourself

That completes the Phase 1 foundations. From here you can branch out — into physics, biology, and beyond — and every new lesson slots straight into the library.