Year 4 · Science · Chemical sciences
Melting and freezing
Students observe how heating makes solids such as ice, butter and chocolate melt into liquids, and how cooling can turn them back into solids.
Awaiting educator review. This material was drafted by our content team with AI assistance and is waiting for review by a qualified educator. Please check it suits your child before using it. Created 10 October 2026.
These lessons were written around Australian Curriculum strands and matched to New Zealand year levels by age (NZ Year 1 is the first year of school). They are not yet mapped to The New Zealand Curriculum, so check them against your own learning programme.
Learning goals
Learners will
- Describe the difference between solids and liquids.
- Explain that heating can melt a solid and cooling can freeze a liquid.
- Compare how quickly different solids melt in the same conditions.
Success looks like
- I can sort materials into solids and liquids.
- I can explain what melting and freezing mean.
- I can predict and test which solid will melt first.
The big idea
Materials can be solid or liquid (or gas, which we will learn about later). A solid keeps its shape. A liquid flows and takes the shape of the container it is in.
When a solid is heated enough, it melts and becomes a liquid. Ice melts into water, and chocolate melts in a warm hand.
When a liquid is cooled enough, it freezes and becomes a solid. Water in the freezer turns into ice.
Different materials melt at different temperatures. Ice melts at 0 °C. Butter and chocolate melt at warmer temperatures, which is why they stay solid in the fridge and go soft on a hot summer day.
Melting and freezing can be reversed. Melted chocolate can be cooled and set solid again. It is still chocolate, just in a different shape.
In a fair test we keep everything the same except one thing. To compare melting, we use same-sized pieces, the same plates and the same warm spot.
Worked examples
Which melts first?
An ice cube, a piece of butter and a piece of chocolate (all the same size) are put on plates in a sunny window. Which melts first?
- Predict and write down your guess.
- Put all three plates in the same sunny spot at the same time.
- Check every five minutes and record what you see.
- On a warm day the ice usually turns to liquid first because it melts at the lowest temperature (0 °C).
Answer: Usually the ice melts first; butter and chocolate soften more slowly.
Juice ice blocks
How can we turn juice into a solid?
- Pour juice into an ice-cube tray.
- Put the tray in the freezer for several hours.
- The cold makes the liquid juice freeze.
Answer: Cool it in the freezer so it freezes into a solid.
Practice check
Have a go, then check your answers. Each answer comes with an explanation.
Answer guide for parents
Which of these is a liquid at room temperature?
Milk — Milk flows and takes the shape of its container, so it is a liquid.
What makes ice melt?
Heating it — Heating makes solids melt.
Why does chocolate melt in a car on a hot summer day?
It gets warm enough to melt — A hot car warms the chocolate above its melting temperature.
Melted chocolate is put in the fridge. What happens?
It becomes solid again — Cooling makes the liquid chocolate set solid again.
In a fair test of melting, what should be different?
Only the type of material — Only one thing should change: here, the material being tested.
At what temperature in degrees Celsius does ice melt? (number only)
0 — Ice melts (and water freezes) at 0 °C.
Water changing into ice is called f_______.
freezing — A liquid turning into a solid when cooled is freezing.
Is an ice cube a solid or a liquid?
solid — Ice keeps its shape, so it is a solid.
Watch out for
- Some children think melting makes a material lighter or 'disappear'. A melted ice cube makes the same amount of water.
- Children may think only ice melts. Many solids melt, including butter, chocolate, wax and metals (at very high temperatures).
- Some think sand is a liquid because it can be poured. Each sand grain is a tiny solid.
Tips for parents
- Cut the butter and chocolate into pieces of the same size so the test is fair.
- Take photos every five minutes so your child can line them up and compare.
- Safety: use only sunlight or warm tap water for heating; no stovetops, candles or boiling water for this activity.
Go further
- Make fruit-juice ice blocks and time how long they take to freeze.
- Hold an ice cube competition: who can keep an ice cube solid the longest using a cloth, foil or a cup?
- List five solids and five liquids in your kitchen.