Ratio of inertia force to surface tension is known as

Explanation:

• Forces encountered in flowing fluids include those due to inertia, viscosity, pressure, gravity, surface tension and compressibility.

These forces can be written as follows:

Reynolds number (Re): 

• It is defined as the ratio of inertia force to viscous force.
• \({\rm{Re = }}\frac{{{\rm{\rho Vl}}}}{{\rm{\mu }}}\)

Froude number (Fr): 

• It is defined as the ratio of inertia force to gravity force.         
• \({\rm{Fr = }}\frac{{\rm{V}}}{{\sqrt {{\rm{gL}}} }}\)

Weber number (We): 

• It is defined as the ratio of the inertia force to surface tension force.
• \({\rm{We = }}\frac{{{\rm{\rho }}{{\rm{V}}^{\rm{2}}}{\rm{l}}}}{{\rm{\sigma }}}\)

Mach number (M): 

• It is defined as the ratio of inertia force to velocity of sound.
• \({\rm{M = }}\frac{{\rm{V}}}{{\rm{c}}}{\rm{ = }}\frac{{\rm{V}}}{{\sqrt {\frac{{{\rm{dP}}}}{{{\rm{d\rho }}}}} }}\)