Physics · KS3 and GCSE · Interactive lesson
Sound: longitudinal waves, pitch and echoes
Watch particles vibrate while a sound disturbance travels. Separate pitch from amplitude and follow an echo’s there-and-back journey.
Choose your view
Explore an interactive example, then try the questions at your own pace.
KS3 / GCSE · start with the idea
By the end of this lesson: Distinguish a sound wave’s travel from its particles’ vibration.
The interactive diagram and controls are in Stage 2, “Explore one example”. Read the idea here, then try it next.
- Sound in air is a longitudinal wave: air particles vibrate back and forth along the wave’s direction.
- The disturbance transfers energy while particles move around their usual positions.
- Higher frequency means higher pitch. Greater amplitude usually means a louder sound when other conditions are unchanged.
Useful starting points
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What do the words mean?
- Longitudinal
- The vibrations are along the direction the wave travels.
- Compression
- A region where particles are closer together than usual.
- Rarefaction
- A region where particles are farther apart than usual.
- Frequency
- Complete vibrations each second, measured in hertz.
- Amplitude
- The greatest distance a vibrating particle moves from its usual position.
- Echo
- A reflected sound that returns to a listener.
Change the example
This is the lesson example. Your practice question uses its own numbers.
Something to try
Play the motion. Keep amplitude the same and change frequency. Then keep frequency the same and change amplitude. Which change represents pitch?
Notice what changes
How particle motion works +
Starts paused. Press Play, then add energy to see the warmer particles move faster.
Particles keep the same size. Liquid particles move around; solid particles vibrate around fixed positions. This is a simplified model, with the change in motion exaggerated to make it easier to see.
About the playback +
About this model
A simplified longitudinal wave in air. Particle size and displacement are exaggerated and not to scale. The inset enlarges the marked particle’s movement by a further factor of eight. The model runs 200 times slower than the represented sound; displayed animation seconds are not the real oscillation period. The wavelength bracket uses a 2 m horizontal reference. ≈ marks a rounded wavelength. Sound speed is fixed at the given 340 m/s; amplitude changes do not alter it in this model.
More about this diagram
Still picture. Play particle motion in Stage 2.
400 Hz: 400 vibrations each second
Still picture of the example from Stage 2. Use the back arrow to change it.
Work through it
Starting example: read the steps below
- The frequency is 400 Hz: 400 complete vibrations per second.
- Each dot moves back and forth around its usual position; it does not travel all the way across with the wave.
- Amplitude 2 is a relative movement size, not a measured sound level.
- Increase frequency to represent a higher pitch. Increase amplitude to represent a louder sound when other conditions stay the same.
Try on your own
Your turn. No rush.
Question 1
A sound’s frequency increases while other conditions stay the same. What happens to pitch?
About these questions
Questions appear in a mixed order. Work at your own pace and stop whenever you like.
These questions use their own numbers, separate from the lesson example. You can stop whenever you like. Answers last for this visit to the page.
A good place to pause
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Can you explain particle motion, wave travel, pitch and amplitude without mixing them up?
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Notes for parents and tutors
These lessons cover selected KS3 and GCSE ideas for England; they are not a complete course. The level notes explain where GCSE methods or optional extensions begin. Maurice can help you choose material for your course and exam board.
The content draws on the DfE Maths curriculum, DfE Science curriculum and AQA GCSE Physics specification. Level labels are guidance, not exam-board endorsements. For AQA Radioactivity, calculating net decline as a ratio is Higher-tier work. Net means the overall change; ask Maurice whether this extension is relevant to your course. Explanations and practice were reviewed during development on 21 October 2026; Maurice should check their fit before assigning work.
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