A wave is an energy transfer through a medium without the medium itself moving very far from its equilibrium position. For instance, think about a wave in the ocean; it moves forward even though the water particles stay in place.

The speed of a wave (v) is determined by its wavelength (λ) and period (T). The formula for wave speed is given by

v = \(\frac λT\)

But, we know that the frequency of a wave (f) is the inverse of its period

f = \(\frac 1T\)

So, we can also write the wave equation as

v = fλ

Example 1: String wave

If you're moving a stretched string up and down at a regular interval, you create a wave. For example, if the wavelength is 1.1m and you move it every 0.60s (period), you can calculate the wave's speed

v = \(\frac λT\) ​= 0.601.1 ​= 1.8ms⁻¹

Example 2: Lake wave

Imagine you're observing a wave on a lake. You notice the wave has moved 0.60m in 0.25s and has a wavelength of 2.8m. You can calculate its speed

v = \(\frac {0.60}{0.25}\) ​= 2.4ms⁻¹

And its period

T = \(\frac λv\) ​= \(\frac {2.8}{2.4}\)​ = 1.2s