Velocimetry refers to the study of the flow of fluids. It is very important in the field of fluid dynamics and in the design of equipments, such as, pumps and turbines.
The flow of liquids can be studied by adding small materials such as bits of paper or styrofoam in water. This helps the observer to track the movement of the flow.
The particles for observations used should have the same density as the fluids.
Velocimetry can also be done using non contact methods such as with the use of lasers. Laser Doppler velocimetry is a method, which uses two beams of lasers to analyze the flow of a fluid.