Traveling Waves
Pluck string, see pulse travel. Builds on The Wave Equation.
You’re watching a transverse wave travel along a long rope. A friend ties a red ribbon to one point on the rope. The wave pulse approaches at 5 m/s.
As the wave passes, how does the red ribbon move?
The ribbon moves up and down but doesn’t travel with the wave! In a transverse wave, each particle oscillates perpendicular to the direction the wave travels. The wave carries energy, not matter. The pattern moves at 5 m/s, but the ribbon just bobs in place — wave speed and particle speed are completely different things.
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Watch the highlighted particle as the wave passes through. Notice it moves only up and down while the wave pattern travels to the right. Compare wave speed vs. particle speed in the data panel.
v = √(T/μ)
Wave speed depends only on the medium’s properties (tension and density), NOT on amplitude or frequency. Shake the rope faster and you get a shorter wavelength, but the wave speed stays the same!
The wave circles the arena at ~20 seats/second, but each person just stands and sits. The ‘wave’ carries the pattern, not the people — a perfect transverse wave analogy.
A floating buoy bobs up and down as waves pass. The water particles move in roughly circular paths, but don’t travel with the wave. That’s why debris can stay in one area even as waves roll through.
Seismologists distinguish P-waves (longitudinal, faster) from S-waves (transverse, slower). S-waves can’t travel through liquid, which is how we know Earth’s outer core is molten.
A whip crack is a transverse wave that accelerates as the whip tapers. The tip exceeds the speed of sound, creating a miniature sonic boom — that’s the crack!
“Waves are nature’s way of moving energy without moving stuff. The wave races forward; the medium just wiggles in place.”
Traveling Wave Lab
Create transverse and longitudinal waves. Adjust tension, density, amplitude, and frequency. Track individual particles to see how they move as the wave passes through.
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Start with a transverse wave and highlight a single particle. Watch it bob up and down while the wave moves right. Now switch to a longitudinal wave — the same particle oscillates left and right instead. Try doubling the tension: the wave speeds up, but the particle motion doesn’t change!
Wave speed depends on the medium (tension and density), not on how you shake it. Frequency and wavelength adjust to satisfy v = fλ, but v stays fixed by the medium’s properties.