ANS:C - Reynold number

The ratio of the inertia and viscous forces acting in any flow, ignoring other forces, is called the Reynolds number. The Reynolds number (Re) is a dimensionless quantity used in fluid mechanics to predict the flow regime of a fluid flow. It is defined as the ratio of inertial forces to viscous forces and is given by the formula: Re=Viscous ForcesInertial Forces​= ρ⋅v⋅L​/μ Where:

• ρ is the density of the fluid,
• v is the velocity of the fluid,
• L is a characteristic length (such as the diameter of a pipe),
• μ is the dynamic viscosity of the fluid.

The Reynolds number helps determine whether a flow is laminar, transitional, or turbulent. It is widely used in various engineering applications to predict flow patterns, pressure drops, and heat transfer characteristics in pipes, channels, and other fluid systems. Therefore, the correct term for the ratio of the inertia and viscous forces in a flow, ignoring other forces, is the Reynolds number.