One pulse. Two paths.
Explore reflection and transmission where two ropes meet.
What will return?
Pause before the boundary. Will the reflected pulse be a crest or a trough?
Watch the gold point: does the rope travel along with the pulse?
The physics behind the animation
Wave speed: v = √(T / μ), where T is tension and μ is mass per unit length. Both ropes have the same tension. The denser rope has four times the mass per metre and half the wave speed.
A single pulse has a width, rather than a wavelength. Its transmitted width changes in the same ratio as its speed. The transmitted pulse stays upright in both cases.
The model uses ideal, lossless ropes and a massless join. With speeds v₁ and v₂, displacement amplitude coefficients are r = (v₂ − v₁)/(v₂ + v₁) and t = 1 + r. Incident and reflected displacements add on the left during overlap. The join remains continuous.
Here 1/9 of the incident energy is reflected and 8/9 is transmitted. A transmitted displacement amplitude larger than the incident amplitude in the lighter rope does not mean energy has increased. The outer ends are outside the model: no end reflections are shown.