Chapter 1 Flashcards
What is density?
Mass (m) per unit Volume (V), that is, the amount of mass per unit volume. ρ=m/V. Units = kg/m^(3)
2 different types of force in fluids?
- BODY FORCE (NO MOTION)
2. SURFACE FORCE (MOTION)
What are body forces?
Body forces are associated with the action of gravity. This is simply the weight of the fluid particles calculated as W=mg. Although fluid is at rest, it can still gain a force.
What are surface forces?
Surface forces can be written in terms of the normal (Fn) and Tangential (Ft) components to the surface.
Eqn for normal force?
Fn = pA => p=Fn/A (p=pressure)
Eqn for tangential force?
Ft=τA => τ=Ft/A (τ (tau) =shear stress)
What is pressure (in fluid mechanics)?
Pressure is defined as the normal force per unit area, it is also known as the normal stress.
What is stress(in fluid mechanics)?
Stress is defined as the tangential force per unit area.
It is also known as the tangential stress/
What is viscosity?
When a fluid is in motion, the resistance to the movement of one layer of fluid over and adjoining one is referred to as the viscosity of the fluid. That is, the tangential or shear force gives the viscosity. Viscosity is a property of a fluid which determines the amount of resistance to a shear force. Shear forces of a fluid are parallel to the surfaces over which they act, the resisting forces must be in the exactly opposite direction and so they too are parallel to the surfaces.
What happens if there is no shear force?
(No motion), no shear force, no viscous effect.
Can you derive an expression (the Newtonian relation) for viscosity of a fluid between 2 paralled plates, one moving and one fixed?
YES OR NO
What does the Newtonian relation satisfy?
The fact that the shear stress of a fluid is proportional to the rate of deformation (or the strain rate).
What is kinematic viscosity equation?
ν(nu)=μ(mu)/ρ
What can the velocity gradient at the moving wall be approximated as?
y=h, so du/dy=U/h
From this what does the shear stress become?
τ=F/A=μU/h
How to work out the units of μ?
F/A=μU/h => μ=Fh/AU => units of μ = Nm/m^(2)m/s=Ns/m^(2)
What are the two physical causes of viscosity?
- Resistance between the fluid layers. 2. Momentum exchange or transfer while fluid is in motion
What can viscosity be effected by?
Viscosity of a fluid may be affected by the temperature, it is usually a function of fluid temperature T, μ=μ(T).