50-minute lesson
Year 6 Science: Solids, liquids and gases
Lesson objective
- Describe the properties of solids, liquids and gases.
- Show that air is a gas that takes up space.
- Classify everyday materials by their state.
Success criteria:
- I can describe how solids, liquids and gases differ in shape and volume.
- I can show that air takes up space using a cup and water.
- I can sort materials into solids, liquids and gases.
Materials
- A clear plastic cup
- A paper towel
- A large bowl or sink filled with water
- A balloon
- An empty plastic bottle
Introduction
5 minIntroduce today's words:
- state of matter: The form a substance takes: solid, liquid or gas.
- volume: The amount of space something takes up.
- gas: A state of matter that spreads out to fill any container, like air or steam.
- property: A feature we can observe or measure, such as shape, hardness or how it flows.
- evaporation: When a liquid slowly changes into a gas.
Ask your child what they already know about solids, liquids and gases.
Explanation
10 minEverything around us is made of matter, and matter can be a solid, a liquid or a gas. These are called states of matter.
- Solids keep their own shape and volume. A brick stays brick-shaped wherever you put it.
- Liquids keep their volume but take the shape of their container. A cup of water poured into a bowl spreads out, but there is still a cupful.
- Gases have no fixed shape or volume. They spread out to fill any container. Air in a balloon fills the whole balloon.
Even though we cannot see most gases, they are real matter. Air takes up space and has mass. A pumped-up footy weighs very slightly more than a flat one.
Some materials are tricky. Sand pours like a liquid, but each grain is a tiny solid that keeps its shape. Toothpaste and honey are thick liquids or soft solids, and scientists sometimes argue about how to classify them.
Materials can change state. Water can be a solid (ice), a liquid (water) or a gas (water vapour). Puddles dry up after rain because the water evaporates into water vapour.
Worked examples
8 minAir takes up space
Can you push a paper towel underwater in a cup without it getting wet?
Step 1: Scrunch a dry paper towel and push it firmly into the bottom of the cup.
Step 2: Turn the cup upside down and push it straight down into a bowl of water. Keep it level.
Step 3: Lift it straight back out and feel the paper towel.
Step 4: The paper towel is dry because air trapped in the cup took up the space and kept the water out.
Answer: Yes. Trapped air takes up space and stops water reaching the paper.
Classifying states
Classify: milk, a spoon, steam, honey, a rock, air.
Step 1: Ask: does it keep its shape? Spoon and rock do, so they are solids.
Step 2: Ask: does it flow and take the shape of its container but keep its volume? Milk and honey are liquids.
Step 3: Ask: does it spread to fill any space? Steam and air are gases.
Answer: Solids: spoon, rock. Liquids: milk, honey. Gases: steam, air.
Guided practice (do together)
10 min1. Which state of matter keeps its own shape?
(a) Liquid (b) Gas (c) Solid (d) Steam
2. Which statement about liquids is true?
(a) They take the shape of their container (b) They always keep their own shape (c) They spread to fill any space (d) They cannot be poured
3. Why did the paper towel stay dry in the upside-down cup?
(a) The water was too cold (b) Paper cannot get wet (c) The cup was magnetic (d) Air in the cup took up the space
4. Sand can be poured. Why is it still classed as a solid?
(a) Each grain keeps its own shape (b) It is wet (c) It spreads to fill any container (d) It is a gas
Independent practice
12 min5. What happens to a puddle on a sunny day?
(a) It freezes (b) The water evaporates (c) It turns into sand (d) It becomes a solid
6. Which state of matter spreads out to fill any container?
7. What is the gas form of water called? (two words: water ______)
8. Is orange juice a solid, liquid or gas?
Questions to check understanding
- Can you describe how solids, liquids and gases differ in shape and volume?
- Can you show that air takes up space using a cup and water?
- Can you sort materials into solids, liquids and gases?
- What was the trickiest part today?
Answer guide
1. Solid — Solids keep their own shape and volume.
2. They take the shape of their container — Liquids flow and take the shape of their container but keep the same volume.
3. Air in the cup took up the space — Air is matter and takes up space, so water could not get in.
4. Each grain keeps its own shape — Each sand grain is a solid that keeps its shape.
5. The water evaporates — The liquid water changes into water vapour, a gas.
6. gas — Gases have no fixed shape or volume.
7. water vapour — Water as a gas is water vapour.
8. liquid — Juice flows and takes the shape of its container.
Review
5 minRecap the success criteria together. Watch for these common misconceptions:
- Many students think air is 'nothing'. Air is matter: it takes up space and has mass.
- Some think powders like flour or sand are liquids because they pour. Each grain is solid.
- Students may think steam is the white cloud above a kettle. Steam (water vapour) is invisible; the white cloud is tiny droplets of liquid water that have cooled.
Extension activities
- Stretch a balloon over the neck of an empty bottle and stand it in a bowl of warm tap water. The air inside warms, expands and the balloon starts to inflate.
- Draw particle pictures showing how tightly packed particles might be in a solid, liquid and gas.
- Mark the level of water in a glass left on a windowsill and check it each day for a week.
Suggested follow-up
- Revisit solids, liquids and gases tomorrow with two or three quick questions from memory.
- Try the online practice check for this topic and look at any questions that need another go.
Tips for parents
- Do the cup-and-paper-towel test over the sink or outdoors.
- Ask your child to justify each classification with a property: 'It is a liquid because…'.
- Safety: keep children away from boiling kettles; talk about steam from a distance only. Never put a balloon near the mouth of a young child.