Start with a single wave
A sinusoidal wave repeats in space and time. Its amplitude A tells you how far it moves from equilibrium. The wave number k sets its spatial frequency, and angular frequency ω controls how quickly it changes in time.
Add a second wave
For linear waves, superposition is beautifully simple: add their displacements at every point. The violet and green curves represent the two component waves. The dark curve is their sum, not a third independent wave.
Change the phase
Phase describes how far one wave is shifted relative to another. At 0°, matching crests add and the combined amplitude is 2A. At 180°, each crest meets a trough and these equal-amplitude waves cancel. Try the phase slider and look at the result.
Take the idea into the world
Interference connects sound, light, and water waves. This model assumes two ideal, equal-amplitude waves with the same frequency in a linear medium. Different frequencies, unequal amplitudes, and nonlinear media lead to richer behavior.