Home / Learn / Physics / Sound wave visualiserTool #L25 (formerly #1061)

Sound wave visualiser: see compressions and rarefactions, wavelength = v/f, hear the note, echoes and SONAR

Watch air particles bunch into compressions and spread into rarefactions as a sound passes. Slide the frequency and amplitude, switch to water or steel, hear the note, and work out echo distances and sea depth with SONAR.

Keep it one tap away for everyday use.

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  1. Frequency
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  3. Wavelength
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Watch the air

The orange dot is one air particle: it only moves back and forth about its own place, while the bunches (compressions, C) and gaps (rarefactions, R) travel to the right. The line below the particles is the extra air pressure: high at each C, low at each R. The motion is slowed down and the particle movement is hugely enlarged so you can see it. Sound plays only when you press the button; keep the volume low.

Echoes and SONAR

Your ear keeps a sound for about 0.1 s, so a separate echo needs the sound to take at least 0.1 s there and back. Sea water speeds vary with temperature and saltiness (roughly 1,450 to 1,550 m/s), so 1,500 m/s is a round school value.

Try this

  • Double the frequency: the compressions get closer, so the wavelength halves. The speed stays the same.
  • Change only the amplitude: the bunches get tighter (louder) but the wavelength does not change.
  • Switch to water or steel at the same frequency: sound is faster there, so each wave is longer.
  • Warm the air from 0 °C to 40 °C and watch the speed rise by about 0.6 m/s per degree.
  • Move the wall closer than 17 m: the echo comes back too soon to hear it as a separate sound.

Check yourself

What it does

Sound is a wave of squeezes and stretches in the air. This page shows rows of air particles as a sound passes through them: where they crowd together is a compression (higher pressure, marked C) and where they spread apart is a rarefaction (lower pressure, marked R). One particle is coloured so you can see the key idea: each particle only moves back and forth about its own place, while the pattern travels on. Change the frequency and amplitude, warm or cool the air, or send the sound through water or steel, and the numbers update with the formula filled in. Press Play the sound to hear the note. A second picture shows echoes and SONAR.

It follows the school topics on sound: Class 9 Science, Sound (production and propagation of sound, longitudinal waves, frequency, amplitude, speed, echo and SONAR), and Class 11 Physics, Waves (speed of sound in a gas, the displacement and pressure waves). Before this, try standing waves calculator for notes on strings and pipes; afterwards doppler and beats shows how motion changes pitch, and ultrasound calculator goes further with ultrasound.

How to use it

  1. Move the Frequency slider (100 to 1,000 Hz). The bunches get closer as the frequency rises, because the wavelength λ = v / f gets shorter.
  2. Move the Amplitude slider. The particles swing further and the bunches get tighter, which you hear as a louder sound, but the wavelength stays the same.
  3. Pick what the sound travels through. In air, the temperature slider changes the speed. Water and steel use rounded speeds.
  4. Press Play the sound to hear the note (it starts quietly; press again to stop). Nothing plays until you press.
  5. Use Pause to freeze the picture and look at one compression.
  6. Switch the Level to Class 11 to see the speed worked out from v = √(γRT/M), the wave number k, the angular frequency ω, the pressure amplitude, the intensity and the sound level in decibels.

Echoes and SONAR

Slide the distance to a wall. The page works out the time for the sound to go there and back, t = 2d / v, and tells you whether it is long enough (at least 0.1 s) to hear as a separate echo. The SONAR slider is the time a ship waits for the echo from the sea bed; the depth is d = v t / 2.

Worked example

With the page as it opens: 500 Hz in air at 20 °C. The speed is v = √(1.4 × 8.314 × 293.15 / 0.02896) = 343.2 m/s, so the wavelength is λ = 343.2 / 500 = 0.6865 m and the time period is T = 1 / 500 s = 2 ms. On the Class 11 level, with an amplitude of 0.5 µm, the pressure amplitude is 0.649 Pa, the intensity 5.10 × 10⁻⁴ W/m² and the sound level about 87.1 dB.

For the echo, a wall 34 m away sends the sound back after 2 × 34 / 343.2 = 0.198 s, so you hear a separate echo. For SONAR, an echo after 2 s in sea water at 1,500 m/s means the sea is 1,500 × 2 / 2 = 1,500 m deep.

Check yourself

At the bottom are five short questions with fresh numbers each time: wavelength, frequency, time period, the distance to a cliff from an echo, and sea depth from SONAR. Type your answer and press Check; the working appears when you get it right or ask for it. Nothing is saved.

Tips

  • The picture is slowed down 250 times and the particle movement is enlarged thousands of times. Real air particles move less than a thousandth of a millimetre in ordinary speech.
  • Sound needs a medium. In a vacuum there are no particles to push, so there is no sound.
  • The speed of sound depends on the medium and its temperature, not on the frequency or the loudness.

FAQ

Why do the bunches move but the coloured particle does not travel? A wave carries energy, not the air itself. Each particle passes the push on to the next one and then moves back.

Why can I not hear some frequencies? Most people hear from about 20 Hz to 20,000 Hz; the range shrinks with age, and small speakers play low notes poorly.

Is this from NCERT? No. It is an independent study aid that follows the same school topics, with its own pictures and numbers.

Where the numbers come from

  • Sound as a longitudinal wave, v = fλ, T = 1/f, speed of sound in an ideal gas v = √(γRT/M) (Laplace), pressure amplitude Δp₀ = ρvωs₀, intensity I = Δp₀²/(2ρv), sound level 10 log₁₀(I/10⁻¹² W/m²), echo and SONAR d = vt/2: standard physics.
  • Gas constant R = 8.314462618 J/(mol K) (CODATA 2018, exact); molar mass of dry air 0.0289647 kg/mol; γ = 1.4. Speeds in water (about 1,480 m/s) and steel (about 5,900 m/s) are rounded general values.
  • Checked against an independent Python calculation (math module) written for the tests.

Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.

Last updated 2026-11-09.

Change log for Sound wave visualiser

  1. Polish pictures of #1061, #1064, #1068 and #1070 Details on GitHub
  2. Add #1061 Sound wave visualiser Details on GitHub

Every change to fibub

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