Dimensionless Numbers in Hydraulics and Fluid Mechanics – The important dimensionless numbers are Reynold’s number, Froude’s number, Weber’s number, Euler’s number and Mach’s number:

(a) Reynold’s number: It is the ratio of the inertia force to the viscous force.

(b) Froude’s number: It is the ratio of the inertia force to the gravity force.

(c) Weber’s number: It is the ratio of the inertia force to the surface tension force.

(d) Euler’s number: It is the ratio of the inertia force to the pressure force.

(e) Mach’s number or Cauchy’s number: It is the ratio of the inertia force to the elastic force.