What are waves and resonance?
Shake a rope, pluck a string, switch on a microwave: it's the same rule every time, speed = frequency × wavelength. Play with waves on a rope, in air and in light, push a swing and a washing machine into resonance, and find out what really brought down the Tacoma Narrows Bridge.
▶ Play with it · Read the 60-second explainer · Watch the 40-second video
- A wave carries energy, not stuff. Shake a rope and a shape runs along it while each bit of rope only goes up and down. Each shake sends one wavelength, so v = f × λ. The speed belongs to the rope; shaking faster only packs the crests closer.
- Sound is squeezed air. A loudspeaker pushes air into bunches that race away at 343 m/s. Pitch is frequency: A4 is 440 Hz with 78 cm waves. A string or pipe fixed at its ends rings only at fₙ = n v ÷ 2L, the harmonics.
- Light is a wave too. Radio, microwaves, light and X-rays are electromagnetic waves, all at c. A microwave oven's 2.45 GHz waves are 12.2 cm long, making hot spots 6 cm apart, and the door's tiny holes turn them back while light gets out.
- Resonance: push in step. Everything that can wobble has a natural frequency. Push at that rhythm, like a swing every 3 s, and small pushes add up until damping balances them. Washers shudder as they spin through it; a wine glass can shatter.
- Surprises and a myth. Waves add, so they can cancel: calm lines between ripples, beats between close notes. Sound needs a medium, light doesn't. And Tacoma Narrows wasn't simple resonance: a steady wind fed a twisting flutter.
| Term | Meaning |
|---|---|
| Frequency (f) | How many waves pass a point each second, in hertz (Hz). |
| Wavelength (λ) | The distance from one crest to the next. |
| Wave speed | How fast the pattern travels: v = f × λ. Set by the medium, not the source. |
| Standing wave | Two waves travelling opposite ways that add into a pattern of fixed nodes and antinodes. |
| Harmonics | The whole-number multiples of a string's or pipe's lowest frequency: fₙ = n v ÷ 2L. |
| Electromagnetic wave | Linked electric and magnetic fields travelling at c = 299,792 km/s, even through empty space. |
| Resonance | A large response when a system is driven at its own natural frequency. |
| Interference | Waves adding where they overlap: reinforcing in step, cancelling half a wave out of step. |
From Pythagoras's strings to ripples in spacetime: how people learned that sound, light and even gravity travel as waves.
- 530 BCE · Whole-number strings sound sweet (Pythagoras and his followers (attributed), Croton, Magna Graecia)
- 1636 · Mersenne's laws of strings (Marin Mersenne, Paris)
- 1687 · Newton calculates the speed of sound (Isaac Newton, Cambridge)
- 1787 · Sand draws the nodes (Ernst Chladni, Wittenberg)
- 1801 · Light makes interference fringes (Thomas Young, Royal Society, London)
- 1842 · Moving sources change pitch (Christian Doppler, Prague)
- 1865 · Light is an electromagnetic wave (James Clerk Maxwell, London)
- 1887 · Hertz makes radio waves (Heinrich Hertz, Karlsruhe)
The full story, with 19 moments, charts, people and 27 sources: glassbox.how/e/waveclear/history. The data lives in history.json.
Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.
| File | What | Size |
|---|---|---|
glassbox/reel.mp4 |
Reel / Short, with captions and soundtrack | 1080×1920 |
glassbox/video.mp4 |
YouTube video, with captions and soundtrack | 1920×1080 |
glassbox/slide-1…10.jpg |
Instagram carousel | 1080×1350 |
glassbox/thumb.jpg |
YouTube thumbnail | 1280×720 |
glassbox/cover.jpg |
Share card and repo social preview | 1200×630 |
glassbox/history-reel.mp4 |
“History in 10 moments” Reel / Short | 1080×1920 |
glassbox/history-slide-*.jpg |
History carousel | 1080×1350 |
glassbox/post.json |
Post copy and schedule used by the publish kit |
This box has no accounts and no ads, and it ships its own fonts and libraries. When you run it yourself it sends nothing anywhere. On glassbox.how, the site's /bar.js also loads Glassbox's analytics: Google Analytics to count visits (it asks first in the EU, UK and Switzerland, and stays off when your browser sends Global Privacy Control or Do Not Track) and ClickTrust to detect bots.
It remembers a few things in your own browser only, and never sends them anywhere:
| Browser storage key | What it holds |
|---|---|
waveclear.v1 |
Which chapters you have opened, your best quiz scores, and sound on or off. |
Exactly what each one sees is at glassbox.how/privacy.
- Code: MIT. Use it, change it, ship it.
- Explanations, text, images and videos (
glassbox.json,glassbox/): CC BY 4.0. Credit “Glassbox, glassbox.how/e/waveclear”. - Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
- The Glassbox name and logo aren't covered by either licence. See the terms.
Found a mistake? Open an issue. Corrections happen in public.
It's plain HTML, CSS and JavaScript. No build step and no dependencies. Run locally, it contacts no other website.
python3 -m http.server 8000Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.
Then open http://localhost:8000.
| File | What |
|---|---|
index.html, css/app.css |
The page and its styles |
js/app.js, js/stage.js, js/ui.js, js/kit.js |
The shared Glassbox 3D engine: chapters, 3D stage, controls, quiz, video director |
js/chapters/*.js |
One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes |
js/wave.js |
Shared wave maths (v = f λ, notes, a driven oscillator, wavelength colours), chart boards, tones and layout helpers |
glassbox.json |
Title, question, explainer beats, key terms, browser storage and credits shown on glassbox.how |
reel in each chapter |
The storyboard the Glassbox studio records into short videos |
glassbox/ |
The published video, slides, thumbnail and post copy |
fonts/, vendor/three/ |
Self-hosted Geist and Instrument Serif (SIL OFL 1.1) and three.js (MIT) |