Physics Flashcards
The SI units ?
- Seconds: Time
- Meter: Distance
- Mole: Amount of substance
- Ampere: Current
- Candela: Luminous intensity
- Kilo: Mass
- Kelvin: Unit of thermodynamics
Derived units ?
- Force: Newton
- Pressure: Pascal
- Energy: Joule
- Power: Watt
- Frequency: Hertz
- Volume: Cubic meter and Litre
Force?
That which changes the state of rest or motion of an object, a push or pull of an onject.
Newtons second law?
F = MxA
Force of gravity ?
9.81 ms-2
Thus
1kg = 9.81N (or 1N = 102g)
Cricoid force = 30-40 Newtons or 3-4kg
Pressure?
1 Pascal is a pressure of 1N in 1m-2 (102g/m-2)
The surface area is important
Pressure equivalents ?
- 1 Atm = 101325 Pa
- 1 Atm = 101.325 kPa (100 kPa)
- 1 Atm = 1 Bar
- 1 Atm = 760 mmHg
- 1 Atm = 760 Torr
- 1 Atm = 1020 cmH2O
- 1 Atm = 14.5 lb/inch-2 (PSI)
- 1 Torr = 1 mmHg
- 1 kPa = 7.5 mmHg
Absolute pressure ?
Absolute = Guage (137) + Atmospheric pressure (1)
Guage pressure = 137 bar
Absolute pressure = 138 bar
Arterial pressure = guage pressure.
E.g; A-line transducer or BP measurement
Flow ?
- Laminar
2. Turbulent
Laminar flow?
- x2 faster at the centre
- No flow near edges
- Low velocity
- Represented by the Hagen-poiseuille equation
- Re = < 2000
Hagen-poiseuille equation?
Q = Ppi r-4/8nl
P = Pressure change
Pi = pi
r-4 = Radius
n = Viscosity
l = Length
Turbulent flow?
- Constriction resulting in increased velocity
- Higher resistance
- Re = > 2000
Reynolds > 4000 ?
- Increased velocity
- Increased characteristic dimension
- Increased density
- . Decreased viscosity
Reynolds? Turbulent flow
If viscosity is increased then turbulent flow becomes laminar.
p = Density V = Velocity D = Diameter u = Viscosity
p.v.D/u
Helium in bronchospasm?
Helium increases viscosity thus making flow laminar
Tension?
- LaPlace law
- Cylinders = P=T/r
- Spheres = P=2T/r
Tension?
- As diamter becomes smaller, collapsing pressure becomes greater
- Without surfactant the small alveoli collapse and empty into the bigger ones
Bernoulli principle?
- Fluid velocity increases as it passes through a constriction and its static pressure must decrease (conservation of energy)
- Fluid pressure is inversely proportional to its velocity
Venturi effect - Extension of the bernoulli principle?
- Constrictiion, increased velocity and decreased pressure
2. Used in nebulizer masks and atomizers
Coanda effect ?
- Tendency of a fluid to be attracted to a nearby surface
2. This is why ETT has murphy eye
Boyles law?
For a given mass at a constant temperature, the pressure times volume is constant
Application of Boyle’s law? Calculation of cylinder content
P1.V1 = P2.V2
P1 = Guage pressure of cylinder
V1 = Physical volume of cylinder
P2 = Atmospheric pressure
V2 = Actual amount of gas in cylinder
137 bar x 3L = 1 x V2 = 411L
Cylinder content ?
- CO2 & N2O are liquified under pressure and content by weight
- Air, O2, He, Heliox, Entonox - Pressure is proportional to volume. Content measured by guage pressure
Charles law?
For a given mass at constant pressure the volume is directly proportional to the temperaure.
Charles law - Application?
V1/T1 = V2/T2
or
V1.T2 =V2.T1
Gases expand when heated and become less dense –> Convection
Gay-Lussac’s law ?
At constant volume, the absolute pressure of a mass of gas varies directly with the absolute temperature.
Gay-Lussac’s law - Clinical application?
P1/T1 = P2/T2
or
P1.T2 = P2.T1
Filling ratio? - Clinical application of Gay-Lussac’s law
This is the weight of fluid in the cylinder divided by the weight of water required to fill the cylinder.
Cold countries 0.75
Tropics 0.67
Universal gas law ?
PV = nRT
n = number of moles
S.T.P?
Standard temperature = 0 degrees or 273 K
Standard pressure = 1 Atm
Avogadro’s Hypothesis?
Equal volumes of gases at the same temperature and pressure contain equal number of molecules
Mole: Is the quantity of a substance containing the same number of particles as there are atoms in 0.012kg fof carbon ( 6.022 x 10-23)
One mole of any gas at STP occupies 22.4L
Dalton’s law of partial pressure?
The total pressure of a mixture of gases equals the sum of the partial pressure of the individual gases
Critical temperature?
Temperature above which a substance cannot be liquified no matter how much pressure is applied
Above critical temperature the sunstance can only exist as a gas.
Below critical temperature, the substance can be a vapor or liquid
Oxygen = -119 CO2= 31 N2O = 36.5
Critical pressure?
The pressure needed to liquify a gas at its critical temperature.
Oxygen = 50 bar / CO2 = 73 bar / N2O = 72 bar
Critical volume?
The volume occupied by 1 mole of gas at critical temperature and pressure
Tripple point of water?
The temperature and pressure in which water can co-exist in equilibrium in 3 phases .
0.01 degrees and 0.006 Atm
Solubility and Henry’s law?
At constant temperature, the amount of a given gas that dissolves in a volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
More molecules are soluble at higher pressures.
Solubility decreases at higher temperatures.
Application of Henry’s law ?
Divers disease - They must descend and ascend slowly to avoid supersaturation or decompression
Partition coefficient?
- Ratio of the amount of a substance present in one phase as compared to the other.
- Measure of the difference in solubilites between two phases
- Tension is used for dissolved gases in solution
Blood-Gas partition coefficient ?
- Describes solubilities of inhaled anaesthetics in blood
- B/G coefficient is inversely related to the induction rate
- Faster onset and off-set the lower the B/G partition coefficient
Diffusion ?
- Movement from high concentration to low concentration. Passive process driven by gradient and no energy required.
Definition of Fick’s law?
Rate of diffusion is equal to the concentration gradient x Surface area x diffusion coefficient divided by membrane thickness.
Potassium is 30x more soluble than sodium
Proportional to solubility
Proportional to concentration gradient
Proportional to area
Inversely proportional to tissue thickness
Inversely proportional to square root of molecular weight
Raoult’s law?
When a solute is added the chemical potential of a solvent molecule is lowered.
There is lowering of the vapor pressure and freezing point
There is a raise of osmotic pressure and boiling point
Osmometer ?
Measures osmolality of a solution using either reduction in vapor pressure or depression of freezing point.
Wheatstone bridge?
An electrical circuit used to measure the unknown resistance.
Used to measure - Capacitance, inductance and impedence
