A summary of principles as well as some past paper questions and worked solutions and explanations. Made for physics (bio) 134 at Stellenbosch University. Covers topics such as Archemede's principle, density, mass and volume and includes worked examples and past paper questions.
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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^21 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
💡 ΔPForce/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
, 💡 PPatm - 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
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