About Transverse Waves

Why I built this

I am a condensed matter theorist. My research is about what happens to light and to vibrations inside a material — how a pulse of light rearranges the electrons in a crystal, how the atoms in a lattice ripple when something disturbs them. Strip away the formalism and nearly all of it is waves. Transverse and longitudinal motion, wavelength and frequency, energy that travels while the matter stays put: these are not introductory topics I left behind on the way to a research career. They are the working vocabulary of one.

Which is why the way waves are usually introduced has always bothered me. A sine curve printed on a page is a photograph of something that only makes sense as a film. Everyone meets the same frozen S-shape with λ marked between two crests. The picture is not wrong. It is just nearly useless for the one thing that actually matters, which is that the medium moves in one direction while the wave moves in another. You either already see that, or the diagram does not help you see it.

And you can get a long way without seeing it. It is entirely possible to state the definition of a transverse wave correctly, rearrange v = fλ without hesitating, pass the exam — and still not be able to say what is moving, or in which direction, or why sound cannot cross a vacuum when light crosses the whole universe. That is not a failure of effort on anyone's part. It is a limitation of the medium. Motion is difficult to teach with something that does not move.

So this site is the thing I wanted to exist. Every guide here is built around a simulation you can interfere with: drag the amplitude and watch the energy climb with its square, halve the wavelength and watch the frequency double to keep the speed fixed, pause the animation mid-crest and trace the distance down to the rest line yourself. The physics is the same physics as in any textbook. The difference is that it moves, and that you are the one moving it.

What it is not is a shortcut. I have not simplified anything to the point of being untrue, and where the real answer is harder than the usual one — why S-waves stop dead at the outer core, why only transverse waves can be polarized — the page does the harder version properly rather than waving at it.

Who I am

The card above has the formal version. What matters here is narrower than a CV: the subject of these pages — light, vibrations in solids, how energy crosses matter without carrying the matter with it — is what I spend my working life on. I am not writing outside my field, and that is the only real reason I am the one writing it.

Which is a reason to take the physics here seriously, and not a guarantee that every line of it is right. Specialists make mistakes inside their own field and larger ones just outside it, and a site this size holds a great many numbers. If you find one that is wrong, I would far rather hear it than not — see corrections below.

How the pages are built

Each guide starts from a question someone actually typed into a search box, and then answers it properly instead of padding around it. The shape is the same every time: a direct answer first, for the reader who needs one line and nothing else, then the definition, the diagrams, the properties, worked examples, where it shows up in the real world, and how any of it came to be known in the first place.

The interactive pieces are the part I care most about, and they are not decoration. Each one is computed from the actual equations rather than drawn to look approximately right:

• The compression explorer derives the position of each compression centre analytically, so the wavelength measurement stays correct as the wave travels rather than drifting out of step with it.
• The spectrum explorer computes every readout live from c = fλ and E = hf across nineteen orders of magnitude — the numbers are calculated, not looked up from a table.
• The side-by-side simulator runs both wave types off a single shared phase, so the only thing that differs between the two panels is the direction each particle is permitted to move.

The standards I hold these pages to

Accuracy before fluency. Figures are checked against published values, and worked examples are calculated rather than asserted. Where sources genuinely disagree — the exact boundary between two spectrum bands, say, or where ionizing radiation begins — the page says so rather than inventing a precision that does not exist. A confident number is worse than an honest range if the confidence is fake.

No dark patterns. No pop-ups, no newsletter interruptions, no "sign in to continue", no advertising. Analytics counts page views, one small notice says so, and opting out is a single click that actually means something: it stops immediately, deletes the cookies, and never asks again. The detail is in the privacy policy.

Accessible by default. Pages work without JavaScript wherever that is possible — the quiz question bank is fully readable with scripting off. Animations respect prefers-reduced-motion, interactive controls meet minimum touch-target sizes, and every diagram carries a description. A student on a borrowed phone with a bad connection should get the same physics as anyone else.

Corrections welcome, and I mean it. If something here is wrong it should be fixed, and quickly. If you spot an error, an explanation that does not hold up, or a figure that does not match its source, tell me. Specific corrections — the number, the page, what it should be — are the most useful message anyone sends me, and they get acted on rather than filed.

What's here

The site is organised into guides, tools and reference material.

Alongside those sit the wave simulator, the calculator, a 25-question quiz with worked explanations, and a glossary of over a hundred terms that powers the hover definitions you will have noticed on dotted-underlined words throughout the site.

Who it's for

Secondary school through introductory undergraduate physics — GCSE, A-level, IB and first-year university — and anyone who has ever wondered why sound bends around a corner and light does not. I assume no mathematics beyond rearranging an equation, and where something harder turns up, such as the elastic moduli that set seismic wave speeds, I explain it rather than dropping it in and moving on.

If you are a teacher, everything here is free to use in a lesson, and the simulators are built to be projected and argued with. If you are revising at eleven at night the week before an exam, start with the direct answer at the top of whichever page you need and go deeper only if you have time. Both of you are who I had in mind.