Wave Patterns Behind a Moving Object on Water
When an object moves across the surface of deep water, it generates a characteristic V-shaped wake pattern discovered by Lord Kelvin in 1887. Remarkably, the half-angle of this wake is always 19.47 degrees, regardless of the object's speed. This universal angle arises from the physics of deep-water gravity waves: waves of different wavelengths travel at different speeds (dispersion), and the envelope of all circular wavelets emitted along the object's path constructively interferes along two lines at exactly arcsin(1/3) = 19.47 degrees from the direction of motion. Inside this V, a pattern of transverse and divergent waves creates the familiar feathered wake seen behind boats.