Analyse orbital period distance and density data
Separate a distance–period trend from a density comparison using a supplied planetary-model table.
Exam scope and assessment notes
Extended only (Supplement) · Physics 0972, 2026–2028. Use supplied distances, periods and stated orbital models. Drawings are not to scale. Written practice is self-checked. Human subject-teacher review, supervised practical competence 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
- Read a table with units.
- Use density as mass per volume.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does density measure?
What you will learn
- Separate a distance–period trend from a density comparison using a supplied planetary-model table.
- Interpret multiple table columns while keeping trends, ratios and causal claims separate.
Read columns and units before ranking
Use this illustrative table, not measured real-planet values: model A has orbital distance 1 unit, period 1 year and density 5.0 g/cm³; B has distance 2 units, period 3 years and density 3.5 g/cm³; C has distance 4 units, period 8 years and density 1.0 g/cm³. The supplied data show increasing period with distance and decreasing density across these three models.
Density is mass per volume, not total mass. A low-density large planet may still have a much greater total mass than a small dense body. The table’s density column alone therefore cannot rank total planetary masses.
State what the evidence supports
A trend describes the supplied rows. It does not prove that orbital distance alone fixes every planet’s composition or density. In a broader interpretation, the inner-rocky and outer-giant distinction helps explain broad density differences, but additional properties and exceptions need actual data.
Ratios require matching units. Comparing orbital periods in years is acceptable when all rows use years; changing one row to days without conversion produces a false trend. Always identify whether a task asks for a ranking, ratio, difference or mechanism.
Pause and explain
What does the supplied A–B–C table directly show?
Worked example
Using the model table, compare C’s orbital period and density with A’s.
Show the worked solution
- C’s period is 8 years versus A’s 1 year.
- C’s density is 1.0 versus A’s 5.0 g/cm³.
- Compute the independent ratios 8 and 0.2.
Answer C has eight times the period and one fifth the density.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Rank A, B and C by orbital period using 1, 3 and 8 years.
Give me a hint
Read one common-unit column at a time.
Compare my reasoning
- A is 1 year.
- B is 3 years.
- C is 8 years.
A < B < C.
Look for these in your work
- Use the period column.
- State the ranking direction.
Compare model B’s density 3.5 g/cm³ with C’s 1.0 g/cm³.
Give me a hint
Form a ratio in matching density units.
Compare my reasoning
- Use densityB/densityC.
- Calculate 3.5/1.0.
- The ratio is 3.5.
B has 3.5 times C’s density.
Look for these in your work
- Use consistent units.
- Avoid substituting total mass for density.
Can a model with density 1.0 g/cm³ be more massive than one with density 5.0 g/cm³? Explain.
Give me a hint
Use the volume that is absent from the density-only comparison.
Compare my reasoning
- Mass = density × volume.
- A sufficiently large volume can offset lower density.
- Volume data are needed to rank total masses.
Yes; lower density can accompany sufficiently greater volume.
Look for these in your work
- Use the mass–density–volume relationship.
- Identify the missing quantity.
Common mistakes
- Density is not total mass.
- A table trend is not automatically a universal causal law.
- Convert mismatched period units.
What can you explain now?
What does the supplied A–B–C table directly show?
Compare with the explanation
Period increases and density decreases across these rows
This statement reports both observed column trends without claiming an unsupported universal mechanism.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Interpret multiple table columns while keeping trends, ratios and causal claims separate.
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.