Distinguish solid liquid and gas properties
Compare shape, volume, flow and compression under stated ordinary conditions.
Section 2.1.1 · States of matter
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028, section 2.1.1. Distinguish solids, liquids and gases and name the required changes among them. Direct solid-to-gas and gas-to-solid changes are not required in this section. Written practice is self-checked. Human subject-teacher review, supervised practical experience and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Distinguish shape from volume.
- Describe observations without assuming what they prove.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which observation concerns volume rather than shape?
What you will learn
- Distinguish the characteristic shape and volume of each state.
- Use flow and compressibility as supporting observations.
Shape and volume give different clues
A solid normally retains its own shape and volume under the ordinary conditions used in this model. A liquid has a definite volume but takes the shape of the part of its container that it occupies. A gas has neither a fixed shape nor a fixed volume: it spreads to fill its accessible container. A gas is not necessarily air; water vapour, for example, is a gaseous state of water.
Pouring the same liquid between two differently shaped vessels changes its shape without automatically changing its volume. The height of its surface alone is not a volume measurement unless the vessel's geometry or calibration is known. A gas may occupy a larger or smaller volume when the container or conditions change; this does not by itself mean that more substance was added.
Flow and compression support the classification
Liquids and gases are fluids: they can flow. A gas is readily compressed compared with a typical solid or liquid. The large reduction in a gas sample's volume under compression is a useful distinguishing observation. Solids and liquids are approximately incompressible for these ordinary comparisons, not mathematically impossible to compress under any force.
State the conditions of a comparison. Heating a solid enough may change its state, and a sufficiently strong force may deform it. Those possibilities do not remove the useful distinguishing properties under the stated conditions. One observation such as 'it moves' does not settle a state; a solid object can move as a whole without being a fluid.
Pause and explain
A liquid is poured into a wider vessel with no loss or state change. Must its volume decrease?
Worked example
A sample keeps volume but changes shape when poured. Another fills the available vessel and is readily compressed. Classify them.
Show the worked solution
- The first sample retains volume but adopts a container shape.
- Those properties identify a liquid in this ordinary comparison.
- The second fills its accessible vessel and compresses readily, identifying a gas.
Answer First: liquid. Second: gas.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify a sample with its own shape and volume, one with fixed volume but container-dependent shape, and one filling all accessible space.
Give me a hint
Compare both shape and volume before naming each state.
Compare my reasoning
- Own shape and volume identify a solid.
- Fixed volume but adaptable shape identify a liquid.
- Filling accessible space with no fixed volume identifies a gas.
Solid; liquid; gas.
Look for these in your work
- Use both properties.
- Keep the descriptions tied to the conditions.
A sealed gas sample can be squeezed from 80 to 40 cm³. A liquid transferred without loss still measures 40 cm³. Explain the contrasting observations.
Give me a hint
Distinguish changing gas volume from changing liquid shape.
Compare my reasoning
- The gas sample is readily compressible.
- The liquid keeps its measured volume during transfer.
- Both can have container-dependent shape, so shape alone would not distinguish them.
The gas compresses readily; the liquid retains volume while taking a new shape.
Look for these in your work
- Use the volume evidence.
- Do not assume the gas gained or lost substance.
A solid ball rolls across a table. A student calls it a liquid because it moves. Correct the classification using relevant properties.
Give me a hint
Whole-object motion is different from flowing to take a container's shape.
Compare my reasoning
- The ball moves as a whole.
- It still retains its own shape and volume under the stated conditions.
- Movement alone does not identify a fluid or a liquid.
It remains solid; rolling alone is not evidence of liquid flow.
Look for these in your work
- Choose distinguishing properties.
- Separate movement from state.
Common mistakes
- A changing liquid shape is not necessarily a changing volume.
- Gas does not mean air.
- Approximately incompressible is not an absolute claim.
What can you explain now?
Which state usually has its own shape and volume?
Compare with the explanation
Solid.
A solid retains both under the stated ordinary conditions.
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Make it stick
Distinguish each state's shape, volume, flow and relative compressibility, and explain a limitation of a single observation.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.