Lecture 2: Fluids Flashcards
What is a fluid?
A material that has the ability to flow
Does a fluid have to be a liquid?
No, both liquids and gases are considered fluids
What causes fluids to flow?
Basic forces like gravity or pressure
Fluids and containers
Fluids assume the shape of their containers, unlike solids, which retain their shape
What is hydrostatics?
The study of fluids that are NOT moving
What are two important properties of hydrostatics?
Density and pressure
What is hydrodynamics
The study of fluids in motion
Pressure =
Force/area
How do you increase pressure?
Increase force or decrease area
How do you decrease pressure?
Decrease force or increase area
At the same depth in a fluid, fluid exerts ___ pressure in all directions
The same
What is Pascal’s principle?
The pressure applied to a confined fluid increases the pressure throughout the fluid by the same amount
Example: If you increase the pressure on a contained fluid by 5 psi, the pressure everywhere in the fluid goes up by 5 psi
If you’re applying a pressure of 3 psi on the plunger of a syringe with a plugged needle, how does the pressure in the barrel compare to the pressure in the needle?
Pressure is equal throughout (Pascal’s principle)
What is Archimedes Principle?
An object immersed either totally or partially in a fluid feels a buoyant force equal to the weight of the fluid displaced
If the density of an object is greater than the density of the fluid, then the object will ___
Sink
If the density of the object is less than the density of the fluid, then the object will ___
Float
If the object sinks, the buoyant force is ___
LESS than the true weight of the object
If the object floats, the buoyant force is ___
GREATER than the true weight of the object
What is a hydrometer?
A device used to measure the specific gravity of liquids
What are two types of flow?
- Laminar
- Turbulent
What is laminar flow?
Unchanging flow pattern, smooth and orderly
What is turbulent flow?
Continuously varying pattern of flow, abruptly changing and chaotic
In anesthesia, we strive for…
LAMINAR flow
What is flow rate?
The volume of fluid passing a particular point per unit time (i.e.: 3L/min)
Narrowing causes speed to…
Increase tremendously
Narrowing causes flow rate to…
Remain the same
Fluid flows at a ___ speed through the narrow part of the tube
Greater
What is Bernoulli’s Principle?
As the speed of a fluid increases, the pressure exerted by the fluid decreases
What was discovered by the Venturi tube flowmeter?
The pressure is lower in the narrow part of the tube; basis of a nebulizer treatment
What is viscosity?
A measure of a fluid’s resistance to flow
Fluids with high viscosity flow…
Do not flow very readily (i.e.: honey)
Fluids with low viscosity flow…
Flow more easily (i.e.: water)
The closer a molecule is to a wall…the ___ it moves
Slower
What is Poiseuille’s Law?
The laminar flow rate of an incompressible fluid is proportional to the fourth power of the radius of the tube it is flowing through
Poiseuille’s equation applies to…
Laminar flow only
What are 3 factors that flow type depends upon?
- Speed
- Density
- Viscosity
What are 3 possible ways to increase the fluid flow rate through a catheter or needle (according to Poiseuille’s Law)?
- Raise IV bag height or add a pressure bag to IV bag
- Use a larger gauge IV catheter
- Use a shorter length catheter
What is Reynold’s number?
Reynold’s number is a dimensionless quantity that is used to characterize fluid flow; it is the measure of the tendency for turbulence to occur
When Reynold’s number rises above 2000, what happens?
Turbulence will usually occur, even in a straight, smooth vessel
Reynold’s number is proportional to what 3 quantities?
- Density
- Velocity
- Tube diameter
Reynold’s number is inversely proportional to…?
Viscosity
