Physics Ch 4. Fluids Flashcards
Fluids
Substances that have the ability to flow and conform to the shape of their containers, can exert perpendicular forces but not shear forces, includes liquids and gases
Solids
Do not flow and they retain their shape regardless of their containers
Density
Mass per unit volume of a substance
Pressure
Defined as a measurement of force per unit area, it is exerted by a fluid on the walls of its container in an objects placed in the fluids, it is a scaler quantity and has magnitude only and no direction, the pressure exerted by a gas against the walls of its container will always be perpendicular to the container walls
Absolute pressure
The sum of all pressures at a certain point within a fluid, it is equal to the pressure at the surface of the fluid (usually atmospheric pressure) plus the pressure due to the fluid itself
Gauge pressure
The difference between absolute pressure and atmospheric pressure, and liquids gauge pressure is caused by the weight of liquid above the point of measurement
Pascals principal
States that a pressure applied to an incompressible fluid will be distributed and diminished throughout the entire volume of the fluid
Hydraulic machines
Create based on the application of pascals principle to generate mechanical advantage
Archimedes principle
Burns the buoyant force, when an object is placed in the fluid the fluid generates a buoyant force against the object that is equal to the weight of the fluid displaced by the object
Buoyant force
Force generated by a fluid against an object that is equal to the weight of the fluid displaced by the object, the direction of the buoyant force is always opposite of the direction of gravity, if the maximum buoyant force is larger than the force of gravity that object will float (this will be true of the object is less dense than the fluid it is an), if the maximum buoyant force is more than the force of gravity the object will sink (this will be true if the object is more dense than the fluid it is in)
Cohesive forces
Between other molecules of the same fluid, gives rise to surface tension, experienced by fluids
Adhesive forces
Between molecules of different materials, experienced by fluids
Fluid dynamics
Is a set of principles regarding actively flowing fluids
Viscosity
A measurement of a fluids internal friction
Viscous drag
A non-conservative force generated by viscosity
Fluid flow
Can either be laminar or turbulent, on the MCAT incompressible fluid’s are assumed to have laminar flow and a very low viscosity allowing us to assume conservation of energy
Poiseuilles law
Relationships determine the rate of laminar flow
Continuity equation
Statement of the conservation of mass as applied to fluid dynamics
Bernoullis equation
An expression of conservation of energy for a flowing fluid, this equation state that the sum of the static pressure and the dynamic pressure will be constant between any two points in a closed system
Venturi effect
For horizontal flow there is an inverse relationship between pressure and speed, and in a close system there is a direct relationship between cross-sectional area and pressure exerted on the walls of the tube
Circulatory system fluids
Behaves as a close system with non-constant flow, resistance decreases as a total cross-sectional area increases, arterial circulation is primarily motivated by the heart, venous circulation has three times the volume of arterial circulation and is motivated by the skeletal musculature and expansion of the heart, inspiration and expiration create a pressure gradient not only for the respiratory system but for the circular system as well, air at the alveoli has essentially zero speed
Weight of a volume of a fluid equation
Fg = rhoVg
Specific gravity equation
SG = rho/1
Pressure equation
P = F/A
Absolute pressure equation
P = P0+rhogz
Gauge pressure equation
Pgauge = P-Patm = (P0+rhogz)-Patm
Pascals principle equation
P = F1/A1 = F2/A2
F2 = F1(A2/A1)
Buoyant force equation
Fbouy = rho_fV_fluiddisplacedg = rho_f*V_submergedg
Poiseullies law equation
Q = pi*r^4DELTAP/8/nu/L
Critical speed equation
v_c = N_R*nu/rho/D
Continuity equation
Q = v1A1 = v2A2
Bernoullis equation
P1+1/2rhov1^1+rhogh1 = P2+1/2rhov2^1+rhogh2
