Ripple tank
A ripple tank can be used to investigate the The number of waves produced each second. The unit of frequency is hertz (Hz)., The length of a single wave, measured from one wave peak to the next. and the speed of water waves.
A ripple tank is a transparent shallow tray of water with a light shining down through it onto a white card below.
The light allows you to see the motion of the ripples created on the water's surface more easily.
Ripples can be made by hand but to generate regular ripples it is better to use a motor.