L1 - 3 Flashcards
What is fluid
And mechanics
And fluid mechanics ?
Fluid: A substance that flows(deforms) when a force is applied (shear stress) (e.g., liquids and gases).
Mechanics: The study of how objects behave under forces and movements.
Fluid Mechanics: The study of fluids at rest (fluid statics) and in motion (fluid dynamics).
Write the characteristics of gases, liquids and solid
1-shape and volume
2- compressibility
3- flow ability
noteful://open?docid=YPIBPUShRMOjn62VBEH2RA&pageid=TIVaQliqSleMLir1sndYvQ
Fluid mechanics usage
- Gas turbine
- Rocket Engine
- Submarine
- Refrigeration system
- Aircraft
- Water pipe
what Comprisable and Incompressible fluids depend on ? explain it
Density
Constant => Incompressible fluid ex: liquids (water)
Variable => Compressible fluid ex: gas ( air, oxygen, helium )
what is Stress ? write the types with explanation
Stress : force per unit area acting on surface
1- Normal stress , ex: pressure is N/m2 =pascal
2- Shear stress , is a tangential stress on surface
Illustrated on the surface of an object
explain the act of Shear stress on solid and fluids ?
notes
Properties of fluids
1- describe Velocity . draw
1- When fluid flows over a stationary plate, the
velocity at the surface is zero due to friction.
2- The velocity increases with distance from the
plate as friction between fluid layers is lower.
3- This variation in velocity creates a velocity
gradient.
4- Shear stresses develop in the fluid due to
differences in velocity between layers.
Properties of fluids
2-what is Viscosity:
measure of a fluids ‘stickiness’ , resistance to deformation or flow varies with fluid types and temperature.
what Newton’s Law of Viscosity ?
draw and explain
The shear stress between adjacent fluid layers is proportional to the velocity gradients between the two layer.
at the top Slope is small the fluid layers moving almost
same velocity -shear stress very small -
*Relationship between the shear stress and
velocity is linear
*Higher shear force means higher
deformation
The slope is large > shear stress also large
describe High viscosity fluids, Low viscosity fluids which how can resist deformation give examples
draw
Viscosity is the ratio of shear stress to the rate of deformation
(velocity gradient) in a fluid.
- High viscosity fluids, like oil, resist deformation
and flow slowly. - Low viscosity fluids, like air, deform easily and
flow quickly.
Viscosity varies with ?
fluid type and
temperature; for example, heating a liquid
typically decreases its viscosity.
explain Viscosity and Temperature and pressure
draw
1- Liquids: As temperature increases, viscosity
decreases because higher temperatures reduce
cohesive forces between molecules, allowing them to
move more freely.
2- Gases: As temperature increases, viscosity increases
due to enhanced molecular activity and collisions.
Pressure Effects on Viscosity:
1- Liquids: Viscosity increases with high pressure, as
molecules are forced closer together, enhancing
intermolecular interactions.
2- Gases: Viscosity is relatively unaffected by pressure
under normal conditions.
Types of fluids
Newtonian
- follow Newton’s law of viscosity
(air, water)
- Do not change its viscosity no
matter how much force applied
Non-Newtonian
- does not follow Newton’s law of
viscosity
Such as :
1- Dilatant : viscosity increase s the force
applied on the fluid ex: corn starch with
water
3-Pseudo plastic : viscosity decreases as
the force applied on the fluid ex:
ketchup ,paint
3-Bingham plastic : fluid does not move or
deform til there is critical stress ex:
toothpaste
Dilatant-shear thickening fluid
A shear thickening fluid stays liquid until a strong force is
applied, then it hardens like a solid.
Why liquids turn to solid?
When a liquid like a starch mixture is stirred slowly, its particles roll over
each other, allowing it to flow like a liquid. However, when a stronger force
is applied, the molecules straighten and tangle, making the mixture rigid
like a solid. Once the force is removed, the molecules return to their
original shape, allowing the mixture to flow again.
