The speed of a wave is how far the wave travels each second. It is linked to the frequency and the wavelength by the equation:
wave speed (m/s) = frequency (Hz) × wavelength (m)
This works because each second f waves pass a point, and each wave is one wavelength long. So a wave with a frequency of 5 Hz and a wavelength of 2 m travels 10 m every second, giving a speed of 10 m/s. Speed is in metres per second, frequency in hertz and wavelength in metres. A wave with a frequency of 10 Hz and a wavelength of 6 m has a speed of 60 m/s, and a wave of speed 6 m/s with a wavelength of 2 m has a frequency of 3 Hz. The equation can be rearranged: frequency = speed ÷ wavelength, and wavelength = speed ÷ frequency.
In a given medium the wave speed is fixed. This means that if the frequency increases, the wavelength decreases. Doubling the frequency halves the wavelength. In a ripple tank you can find the speed of water ripples by measuring the wavelength with a ruler and reading the frequency from the vibrating dipper.