Sound waves – frequency (pitch) and amplitude (loudness)
Integrated ScienceLight & SoundAges 12–13
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Light & Sound
A speaker membrane vibrates, causing air particles in a tube to bunch together and spread apart; these compression and rarefaction layers propagate as a sound wave while each particle merely oscillates about its rest position. Drag the frequency and amplitude sliders: a higher frequency vibrates the membrane faster, giving a higher pitch, while a larger amplitude makes particles vibrate more strongly, giving a louder sound. A displacement-vs-time graph shows the period T = 1/f; choose a medium (air, water, steel, vacuum) to see how the speed of sound differs and that sound cannot travel through a vacuum.
Lesson: Sound waves; Loudness and pitch
What it shows
Sound is a longitudinal wave: a vibrating source pushes the particles of a medium together (compressions) and pulls them apart (rarefactions), and this pattern travels outward while each particle only oscillates about its rest position. Frequency, the number of vibrations per second, sets the pitch, and the period is T = 1/f. Amplitude sets the loudness. The wavelength follows from λ = v/f, so it depends on both the source and the medium: of the media shown, sound is fastest in steel and slowest in air, and it cannot travel through a vacuum at all.
How to use
With the Medium set to Air, change only the Frequency: watch how fast the speaker membrane moves, how the period on the displacement-vs-time graph shortens, and how close the compressions get. Then keep the frequency fixed and change the Vibration amplitude. Use the Slow-motion factor to follow a single particle and confirm that it does not travel with the wave. Finally, switch the Medium to Water, Steel and Vacuum and compare the speed and spacing of the compressions.
Parameters you can change
- Frequency 100–1000 Hz
- Vibration amplitude 1–10 mm
- Medium Air (343 m/s), Water (1500 m/s), Steel (6100 m/s), Vacuum (no propagation)
- Slow-motion factor 50–500 ×
- Show displacement-vs-time graph
Questions to explore
- What is the period of a 500 Hz sound, and how does the graph confirm your answer?
- If you double the amplitude but keep the frequency, what changes in the sound and what stays the same?
- Why could astronauts on the Moon not hear each other speak without radios?
