Solids, Liquids and Gases: Year 4 Activities

Properties of solids, liquids and gases in Year 4

Compare shape and volume first. A solid normally keeps both. It may bend, stretch or be squashed, but it does not flow to take the shape of a container. A liquid has a fixed volume but no fixed shape: it flows, forms a pool rather than a pile and takes the shape of the lower part of its container. A gas has neither a fixed shape nor a fixed volume. It spreads out and can escape from an unsealed container.

Gases are often invisible, but they are still matter. Air inside a balloon, syringe or upturned cup occupies space and has mass. This is why an apparently empty container is not truly empty. Use these observations to describe a material’s state and compare its behaviour with other familiar materials.

• Solid: fixed shape and fixed volume.
• Liquid: no fixed shape, fixed volume and able to flow.
• Gas: no fixed shape or volume and spreads through available space.

Classifying tricky solids, liquids and gases KS2 examples

Some materials can mislead pupils if classification is based only on whether something pours. Sand, rice, flour and sugar can be poured, but each sample is a collection of tiny solid grains. A pile changes its overall outline because the grains move around, not because each grain has become a liquid. A sponge is also a solid even though it can change shape when squeezed, because it has its own structure and does not flow to fill a container.

The strongest answer names an observation and links it to a property. Instead of saying “water is a liquid because it is wet”, say that water keeps its volume but takes the shape of the bottom of each container. Instead of saying “air is a gas because it cannot be seen”, show that trapped air occupies space and can be compressed. Comparing and grouping materials in this way builds the evidence language expected in Year 4 science.

Changing state through heating and cooling

A substance can change state while remaining the same material. Melting happens when heating changes a solid into a liquid. Freezing happens when cooling changes a liquid into a solid. Evaporation happens when particles leave the surface of a liquid and form a gas. Condensation is the reverse change, when a gas cools and becomes a liquid. Water makes these changes easy to connect: ice, liquid water and water vapour are different states of the same substance.

Year 4 pupils should observe that different materials change state at different temperatures and record temperatures in degrees Celsius when appropriate. A safe investigation can compare ice cubes placed in different locations, measure how long they take to melt and keep cube size, container and timing method the same. The purpose is to link a measured change to heating or cooling, not to handle hot materials without adult supervision.

A simple properties investigation and recording routine

Choose a small set of familiar samples and decide what evidence will separate the three states. For solids, test whether each sample keeps its own shape when moved. For liquids, pour equal measured volumes into differently shaped transparent containers and observe that the surface and outline change while the amount stays the same. For gases, trap air safely in a balloon or sealed syringe and observe that it occupies space. Do not taste materials or heat them without suitable adult control.

Record the material, prediction, observation and conclusion in separate columns. A useful conclusion follows the pattern: “I classify ___ as a ___ because ___.” If an example seems difficult, repeat the test or choose another observable property rather than changing the definition. Use the observations to explain your classification before moving on to evaporation, condensation and the water cycle.