# Superposition

When waves meet, their displacements add. After meeting they carry on unchanged.

Physics (university) · Part 05: Oscillations and waves · Card 8 of 11 · Last updated 2026-10-19

## Analogy

Two ripples crossing on a pond pass through each other.

## Example

**Adding waves**

In step: 3 + 3 = 6 cm
Opposite: 3 + (-3) = 0 cm

## In practice

Two waves of height 3 cm in step make a 6 cm wave. Out of step by half a cycle, they cancel.

## Practice

### Flashcards

- **What does destructive interference mean?** Waves meet out of step and partly or fully cancel.

## Questions people ask

### What is the difference between constructive and destructive interference?

Constructive interference happens when waves meet in step, so their displacements add to a bigger wave. Destructive interference happens when waves meet out of step, so they partly or completely cancel. Noise-cancelling headphones use destructive interference by playing the opposite wave.

### What is path difference?

Path difference is how much farther one wave travelled than another to reach the same point. If it is a whole number of wavelengths, the waves arrive in step and add. If it is half a wavelength, 1.5 wavelengths and so on, they cancel.

## Related concepts

- [Simple harmonic motion](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-1)
- [Period and frequency](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-2)
- [Mass on a spring](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-3)
- [Simple pendulum](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-4)

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