Waves, sound and light is an interactive 3D walkthrough showing that water ripples, sound and light are all described by one model — the wave: something travels while the medium mostly stays put. You learn to read every quantity off a single wave (amplitude A, wavelength λ, period T, frequency f), tie them together with the wave equation v = λ·f, and follow that same model through sound (decibels, standing waves, the Doppler effect) and light (reflection, refraction, dispersion and the electromagnetic spectrum). It is built for Danish upper-secondary physics (Fysik C/B/A) and covers the wave part of the curriculum end to end.
In a transverse wave the particles move across the direction the wave travels (like a wave on a string or rope), while in a longitudinal wave they move back and forth along the travel direction (like sound in air, which is a pressure wave of compressions and rarefactions). A water surface wave is actually both at once — each water particle traces a small circle.
v = λ·f says a wave's speed equals its wavelength times its frequency, because in one period T the wave advances exactly one wavelength. Combined with f = 1/T it links speed, wavelength and frequency; for light it becomes c = λ·f with c ≈ 3.0·10⁸ m/s.
Because the decibel scale L = 10·log(I/I₀) is measured relative to a reference intensity I₀ = 10⁻¹² W/m², which is the faintest sound a person can hear — not zero sound. 0 dB just means the intensity equals that threshold; doubling the intensity adds about 3 dB and tenfold adds exactly 10 dB.
When a source moves, its wavefronts bunch up ahead of it (shorter wavelength, higher pitch) and stretch out behind it (longer wavelength, lower pitch) — which is why a passing siren drops in pitch. The same effect lets ultrasound measure blood flow, with a shift Δf = 2·f₀·v·cosθ/c_tissue.
Light slows down in water, and because the wavefront's leading edge slows first the whole front swivels and bends toward the normal — this is refraction. The frequency stays the same, so the wavelength shortens, and the bending follows Snell's law n₁·sinθ₁ = n₂·sinθ₂ with n = c/v.