Superposition principle

It means that when two or more waves overlap, the resulting displacement is the sum of the individual displacements. This is why two water ripples can pass through each other and then keep moving as separate ripples.

Constructive interference happens when overlapping waves add together, while destructive interference happens when positive and negative displacements cancel. The classic double-slit experiment demonstrates this with alternating bright and dark bands.

Yes, quantum states can be described as superpositions of possible states until a measurement produces a definite outcome. A common textbook example is an electron spin state written as a combination of spin-up and spin-down.

It works exactly for linear systems, such as ideal small-amplitude waves. In nonlinear systems, like very large ocean waves or distorted amplifier circuits, waves can interact in ways that are not just simple addition.