Types of Forces in Fluid Flow, Inertial Force, Viscous, Gravity, Pressure, Surface Tension, Elastic

In fluid flow problems forces acting on the fluid may be a single one and may not be. May be forces are acting combined. Force affects each particle (almost in case of small flow) and each particle affects the force via transfer of affect from one particle to other, from one layer to another adjacent layer. Fluid Particles resist the forces as per their stamina (Newton’s Third Law of Motion…. Action-Reaction). If Force is more powerful then affect will be shown bare eyes and is the intensity of acted force is very small the flow will be maintained itself.

Here the forces that participate in moving fluid are defined briefly. Each of this force has its affected effect in fluid flow problems. All forces can be defined easily with its name such as Inertial Force includes word inertia means related to Newton’s First law, similarly Gravity Force consists gravity means related to Newton’s Second Law etc…  Hence it is very simple to define any Force with its name basically. Moreover we are providing you here a “TTT” (Tip and Trick of Today) to learn these forces in series. To learn Forces in series is not necessary but yes it is in case of Determination of Dimensionless Numbers (Reynolds, Froude, Mach etc…). TTT is given below in the post that will help you.

Also Read: Basic Definitions in Fluid Mechanics, Properties of Fluid

Inertial Force: As we discussed above the name “Inertial Force” signifies itself linked with Inertia. As Newton’s Second Law of Motion derived the equation

Force = mass x acceleration

Simply this is the way to learn it. Thus Newton’s second law gives the definition of Inertial Force. And normally we say that F = ma, so it is the simplest method to learn it by force definition due to inertia. Inertial Force is indicated by F_i.

(Inertia is the property of anything that helps them to be in a state whether it is in stationary or in motion)

Viscous Force: It implies the viscosity, means the force acted due to viscosity is called “Viscous Force”. And if you remember viscosity exists due to shear stresses in the different layers of flowing fluid. You know the formula for Shear Stress.

i.e. Shear Stress (τ) = Shear Force/Area [or simply τ = F / A, therefore F = τA

Here the Shear Force is Viscous Force, so the formula will

Viscous Force (F_v) = Shear Stress x Area

Thus Viscous Force is the product of these two parameters one of them is the Area upon which the force is acting and another one is the produced shear stress. The symbol used to indicate Viscous Force is

(Viscosity is the basic property of any fluid to flow in different folds means layers, all liquids generally have this property.)

Gravity Force: This force acts due to gravity and due to gravity force acting is

F = mg

(in case of gravity gravitational acceleration is considered instead of acceleration), so this force is “Gravity Force”. It is denoted by F_G.

So make definition for it. Product of mass and gravitational acceleration is “Gravity Force”.

Pressure Force: Think that we are gonna give the definition for pressure. So Pressure intensity will be the product of force and reciprocal of area. Simply the force is Pressure Force and it will be the product of Pressure Intensity and Cross-Sectional Area.  It denotes F_P

Surface Tension Force: For surface tension force we should learn the definition of Tension. It is denoted by F_{ST .}

We know that

T = F / L

Surface tension and the length of surface products this force which acts in flowing fluid.

Elastic Force: Elasticity of any material is defined by Stress, so basically by stress formula. It is denoted by

F_{E .}

Thus product of elastic stress and Area is defined as “Elastic Force”.

Importance of these Forces: Dimensional Analysis is considered with the help of these forces. All the dimensionless parameters are calculated with help of these forces.

Easy and Best Way to learn definition of forces: Just the formulas keep in mind and make definitions your own…

TTT: Suppose that you have seen your result and want to know about your friend then you will ask in Hindi + English “Aai Vi Grand Percentage See ?” { “ vkbZ oh Grand Percentage See ? ” }

This is the Trick of Today learn the above bold words and understand those words as you are using them in your college time to ask your friend using these words.

| When you write this thinking you will write “I V G P S E” |

Here I stands for Inertial, V stands for Viscous, G stands for Gravity, P stands for Pressure, S stands for Surface tension and E stands for Elastic Forces.