Everything is matter
Your toys, your drink and the air you breathe are all made of matter. Matter comes in three main forms, or states: solid, liquid and gas.
Solids
A solid keeps its own shape. If you put a block in a bowl, it is still a block.
- Examples: ice, rocks, wood, a pencil, a spoon
- You can hold a solid in your hand.
Liquids
A liquid flows. It takes the shape of whatever container it’s in, but it doesn’t spread out to fill the whole container.
- Examples: water, milk, juice, honey, oil
- Pour water from a tall glass into a flat bowl. The water changes shape, but there is still the same amount.
- Some liquids flow quickly (water). Others flow slowly (honey).
Gases
A gas spreads out to fill any space. Most gases are invisible.
- Examples: air, steam, the gas inside a balloon
- When you blow up a balloon, the air spreads out to fill the whole balloon.
- You can smell some gases, like the smell of cookies baking.
Comparing the three states
| Solid | Liquid | Gas | |
|---|---|---|---|
| Keeps its shape? | Yes | No | No |
| Flows? | No | Yes | Yes |
| Fills its container? | No | Fills the bottom | Fills all of it |
| Example | Ice | Water | Steam |
Heating changes matter
When you heat some solids, they melt into liquids.
- Ice melts into water.
- Butter melts in a hot pan.
- Chocolate melts in your hand on a hot day.
- Crayons melt in the sun.
When you heat a liquid a lot, it can evaporate and turn into a gas.
- Puddles dry up on a sunny day.
- Wet clothes dry on a clothesline.
- Water boils in a pot and turns into steam.
Cooling changes matter
When you cool a liquid, it can freeze into a solid.
- Water freezes into ice in the freezer.
- Juice freezes into ice pops.
When you cool a gas, it can condense back into a liquid.
- Water drops form on a cold glass of lemonade.
- Your breath makes a mirror foggy.
- Dew forms on grass on a cool morning.
Water changes all the time
Water is special because we see it as a solid, a liquid and a gas every day.
ice → (melt) → water → (evaporate) → water vapour
water vapour → (condense) → water → (freeze) → ice
Some changes can’t be undone
Melting and freezing can go back and forth. But some changes can’t be undone. When you bake a cake, you can’t turn it back into eggs and flour. When you toast bread, you can’t untoast it!
Safety
Always ask an adult before using heat. Steam and hot liquids can burn you.
Common mistakes
- Thinking air is nothing. Air is a gas. It’s real matter, even though you can’t see it.
- Thinking water on a cold glass leaked through. It came from water vapour in the air that condensed.
Try it yourself
- Put an ice cube on a plate in the sun and one in the shade. Which melts first?
- Pour the same amount of water into a tall glass and a flat plate. Does it change shape? Does the amount change?
- Put a cold glass in a warm room. Watch for drops on the outside.
Quick recap
- Matter can be a solid, a liquid or a gas.
- Solids keep their shape; liquids flow; gases spread out to fill a space.
- Heating can melt solids and evaporate liquids.
- Cooling can freeze liquids and condense gases.
- Water can be ice, liquid water or water vapour.