# Wave speed

For any wave, speed equals frequency times wavelength: v = f lambda.

Physics (university) · Part 05: Oscillations and waves · Card 6 of 11 · Last updated 2026-10-19

## Analogy

Counting how many crests pass you each second and how far apart they are.

## Example

**Concert A**

lambda = v / f
lambda = 343 / 440
lambda = 0.78 m

## In practice

A 440 Hz note in air at 343 m/s has a wavelength of about 0.78 m.

## Practice

### Flashcards

- **What is the formula for wave speed?** v = f lambda.

### Interview questions

**Explain how a standing wave forms on a guitar string and find the first three frequencies for a 0.65 m string with wave speed 260 m/s.**

- Two waves moving opposite ways superpose
- Ends are nodes
- f_n = n v / 2L gives 200, 400, 600 Hz

## Questions people ask

### Does a wave's speed depend on its frequency?

For most waves in a given medium, no. Speed is set by the medium, such as air temperature for sound or tension for a string. Changing frequency changes wavelength instead, so v = f lambda stays the same. A higher note has a shorter wavelength but travels at the same speed.

### How fast does sound travel?

In air at 20 degrees Celsius, sound moves at about 343 m/s. It is faster in warmer air, faster in water at about 1480 m/s, and faster still in steel at about 5000 m/s. Sound cannot travel in a vacuum because it needs a medium.

## Related concepts

- [Standing waves](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-9)
- [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)

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