Summary Fluid Mechanics

💧
Fluid Mechanics
What is a fluid?
A substance that changes its shape continuously when a normal stress is
exerted on it

What is the difference between normal stress and shearing stress?
Normal Stress: Either tensile or compressive



💡 Force is perpendicular with the surface




Stress = F orce/Surfacearea

Shearing Stress: Tangential



💡 Force is parallel to the surface


Stress = F orce/SA

Here the surface area is the area that is parallel to the surface and force
and in the same direction as the force

Density

The intensity of a mass



💡 Average Density = ΔMass/ΔVolume




Fluid Mechanics 1

, 💡 Density at a point= dΔMass/dΔVolume as limit of volume tends
to limit 0


Units of kg.m^3

Pressure

Intensity of the Force



💡 Average Pressure= ΔForce/ΔSurface Area




💡 Pressure at a point= dΔForce/dΔSurface Area as Surface area
tends to limit 0


Units of N.m^2 or Pa 1 N.m^21 Pa)



What does it mean if a fluid is static

Sum of all forces = 0 and no Ek because velocity is zero

What is standard atmospheric pressure?

1atm or 760 torr or 101.3 kPa or 1013 millibars

Static fluids

The difference in pressure(ΔP is equal to the pressure due to the weight
of the fluid on the bottom surface area



💡 ΔPForce/Surface Area but since the force here is the weight of
the fluid, ΔP=mg/Volume but Pressure is directly proportional to
depth so, ΔP=mgh/Volume and since Mass/Volume=density,
ΔP=density x g x h


If the surface of the container the fluid is in is at atmospheric pressure,
then to calculate the pressure in the container:




Fluid Mechanics 2

, 💡 PPatm - ΔP where ΔP=density x g x h



U tube




Accessed on 11/06/2020 from
http://www.insula.com.au/physics/1221/L2.html
Pressure at D=atmospheric pressure

Pressure at C Pressure at B Patm- (density of mercury x g x h2



💡 The "U"is the same depth as DC hence the pressure is the same



Pressure above A Patm- (density of mercury x g xh2 - (density of fluid x
g x h1

Concepts of fluid flow

Steady and turbulent: when a fluid is steady the pressure, density and
velocity is constant but in a turbulent fluid it varies all the time

Compressible and in compressible: compressible fluids will undergo a
change in density when there is a change in pressure but in compressible
fluids will have a constant density

Non viscous and viscous: Non viscous fluids flow and undergo no
energy loss while viscous fluids do.



Fluid Mechanics 3