Compare sound speeds in solids liquids and gases
Use the general material ordering with supplied examples and avoid inferring speed solely from density.
Section 3.4 · Sound
Exam scope and assessment notes
Extended only (Supplement) · Physics 0972, 2026–2028. Follow the selected spectrum or sound section. Diagrams illustrate stated ideal models and supplied data. 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
- Explain sound's medium requirement.
- Use v = d/t and v = fλ.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which information is needed to calculate direct travel time?
What you will learn
- Recall that sound generally travels faster in solids than liquids and faster in liquids than gases.
- Use supplied material speeds without making the general rule universal.
Use a general comparison
In general, sound travels faster in solids than in liquids and faster in liquids than in gases. Interparticle restoring interactions and inertia both influence propagation. Density alone is not enough to calculate speed, and the general state ordering is not a universal claim about every possible material.
A supplied example might use 5000 m/s in a metal, 1500 m/s in water and 340 m/s in air. These values illustrate the ordering; they are not required universal constants for all metals, liquids or gases. Temperature and material composition can change the result.
Connect speed to time and wavelength
For an equal 150 m direct path, the supplied speeds give 0.030 s in the metal, 0.10 s in water and approximately 0.441 s in air. The faster material gives the shorter travel time. The path and speed must both be known to compare arrival times.
At a stationary boundary the transmitted sound retains the source frequency in the school model. A changed material speed then changes wavelength through λ = v/f. Do not claim that sound becomes a different frequency merely because it enters water.
Pause and explain
With supplied speeds 5000 m/s in metal and 1500 m/s in water, which gives the shorter equal-path travel time?
Worked example
Compare travel time over 150 m using supplied speeds 5000, 1500 and 340 m/s.
Show the worked solution
- Metal: 150/5000 = 0.030 s.
- Water: 150/1500 = 0.10 s.
- Air: 150/340 ≈ 0.441 s.
Answer Metal fastest arrival, then water, then air for equal paths and the supplied values.
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.
State the general solid/liquid/gas speed ordering.
Give me a hint
Include the qualifier that preserves the scope.
Compare my reasoning
- Sound generally travels fastest in solids.
- It is generally slower in liquids.
- It is generally slower again in gases.
In general: solids > liquids > gases.
Look for these in your work
- Include in general.
- Do not substitute density ordering.
Find the time for 30 m in water at a supplied 1500 m/s.
Give me a hint
Use the stated direct distance and medium speed.
Compare my reasoning
- d = 30 m and v = 1500 m/s.
- t = d/v = 30/1500.
- t = 0.020 s.
0.020 s.
Look for these in your work
- Use the supplied speed.
- Give seconds.
At unchanged 1000 Hz, calculate wavelengths in supplied air speed 340 m/s and water speed 1500 m/s.
Give me a hint
Use λ = v/f in each region while retaining frequency.
Compare my reasoning
- Air λ = 340/1000 = 0.340 m.
- Water λ = 1500/1000 = 1.50 m.
- The changed speed changes wavelength, not the stated frequency.
0.340 m in air; 1.50 m in water; frequency unchanged.
Look for these in your work
- Use each material speed.
- Keep the frequency fixed.
Common mistakes
- The ordering is general, not universal for every material.
- Density alone does not determine sound speed.
- Frequency can remain unchanged while wavelength changes.
What can you explain now?
What is the general state ordering of sound speed?
Compare with the explanation
Solids faster than liquids, which are faster than gases.
Use the general trend with stated materials and conditions rather than as an exception-free law.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Give the general material ordering and calculate times or wavelengths from supplied speeds with appropriate limits.
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.