What is force and the equation for this?
Force is that influence which tends to change the state of motion of an object. Another way to think of force is In Newtons. F=ma
What is a Newton and the equation for this?
That force which will give a mass of 1 kg an acceleration of 1 metre per second per second ie = kg per m squared
Mnemonic: 1N = 1kg·m/s² -> 1 Newton is the force needed to accelerate 1 kg at 1 m/s².
What is pressure and the equation for this?
Pressure if the force applied over a unit area, measured in pascals (P). P = F/A. Makes sense, a narrow pin will have higher pressure because lower area than a wider head pin
What is 1 pascal equal to?
1 pascal is equal to a force of 1 newton applied over an area of 1m squared. Ie N.m-2 this is a small amount given 1N is just 102 grams on earth so we often use kPa
What is Energy? What is work?
Energy is the capacity to do work, measured in joules. Work is described by the equation J=FD where J is work, Force is F and D is distance travelled in direction of the force. Work must be done to move an object. It is a measure of energy transfer that occurs when an object is moved over a stance by an external force
What is a joule?
one joule is the work done when a force of one newton moves one metre in the direction of the force
What is the definition of power and the equation?
The rate at which work is done. It is measured in watts. W = J/s . Ie when cycling watts are how many joules of energy you are putting out per second. The definition of 1 watt = one joule of energy in 1 second
What is laminar flow and what equation describes this?
Laminar flow where any fluid (gas or liquid) passes smoothly along a path. It is demonstrated by Hagen-Poiseuille equation.
Q=πpr4/ 8ηL. with q = flow, p = pressure change (p1-p1) , n is viscosity . Note in laminar flow the fluid in the middle is twice as fast, but the fluid at the edges is near zero velocity
what is turbulent flow and the equation?
turbulent flow = fluid flows unpredictably with multiple eddy current and is not parallel to the sides of the tube which it is flowing. Trick!! no equation as it is unpredictable so can’t be an equation.
What is Reynold’s number (Re)?
An equation can be used to calculate whether fluid flow is likely to be laminar or turbulent
Re = (density of fluid x velocity x diameter) / viscosity of fluid
OVERALL
<2000 = likely laminar, >2000 = likely turbulent
viscosity is important property for laminar flow
density is important property for turbulent flow
What is the Bernoulli principle?
An increase in the flow velocity of an ideal fluid will be accompanied by a simultaneous reduction in its pressure
Think of a ping pong ball in a funnel and then when upside down the ball will stay in place if high flow
What is the Venturi effect?
Think of blowing up my camping mat. The constriction of a fluid to flow ie pursed lips causes the velocity of the fluid (air) to increase as same number of molecules. However this leads to a decrease in pressure directly after the mouth as energy must be conserved. ie kinetic energy to pressure (potential energy). As pressure falls it draws in surrounding air into the space so more molecules ie more air.
This is how Venturi masks and nebulisers work.
What is the first law of thermodynamics?
The law of conservation of energy - energy cannot be created or destroyed but can only change from one form to another
What is the Coanda effect?
The tendency of a stream of fluid flowing in proximity to a convex surface to follow the line of the surface rather than its original course
It is due to moving column of fluid entrains molecules lying close to a surface as they get dragged along by friction. This creates a negative pressure relative to above and therefore is pushed towards the surface
What is heat and temperature?
Heat is transfer of thermal energy between objects of differing temps (in J) - hot to cold
temperature - measure of the mean kinetic energy of the molecules of a substances and the property of matter that determines in which direction heat energy will flow
An object with a higher temperature does not necessarily have more heat energy -> temperature change per unit of heat energy will depend upon specific heat capacity of object
If there is a temperature difference between two systems or objects, then heat will flow between them, along a gradient from hot to cold, until thermal equilibrium is reached. This is regardless of the size of the two objects or the total amount of energy they each contain. A large iceberg holds a large amount of thermal energy because of its immense size, but as this energy is widely dispersed it has a low temperature. If a pot of boiling water is poured onto the iceberg, the water will cool, and the iceberg warm along their temperature gradient, despite the vast difference in the total energy content of the two substances. It is therefore temperature gradients that govern the flow of thermal energy.
What is the triple point?
Temperature at which all three phases of water (solid/ liquid/ gas) are in equilibrium at 611.73 Pa, occurs at 0.01 degrees C
What is Kelvin and celsius?
Kelvin is SI base unit measure of thermodynamics.
To convert Celsius to Kelvin you must add 273.15, and 1 degree centigrade change is 1 kelvin
All calculations with temperature should be done in Kelvin
ie volume of gas at 20 deg C is not double 10, it must rise to 293.15 degrees C before it doubles (566.3K)
What is heat capacity and specific heat capacity?
Heat capacity is the amount of energy required to raise the temperature of an object by 1 Kelvin. Specific heat capacity is…more specific…and is the amount of energy required to raise the temperature of 1 kg of a substance by 1 Kelvin.
ΔQ = c.m.ΔT. where c = specific heat capacity, ΔQ is the amount of heat energy (kJ), m is the mass (kg) and ΔT is the change in temperature.
How is heat lost in an operating theatre?
The mechanisms (and estimated %contribution) of energy loss in the operating theatres are as follows:
Radiation (40%): Energy loss through infrared radiation.
Convection (30%): Energy loss due to air currents which receive thermal energy and then migrate, maintaining a gradient for further energy transfer.
Evaporation (15%): Energy loss due to the latent heat of vaporisation.
Respiratory losses (10%): Further evaporative heat loss (humidification and warming)
Conduction (5%): Direct energy transfer onto surrounding surfaces e.g. operating table
Why in operating theatre do patients lose heat?
Why in the Operating Theatre?
Both regional and general anaesthesia exacerbate the situation, and predispose the patient to temperature loss.
Anaesthetic effects: Paralysis prevents shivering, reduction in muscle tone reduces heat generation, vasodilatory effect of agents increases energy loss, reduction in basal metabolic rate.
Physical effects: Exposure of the skin surface, exposure of the abdomen (laparotomy), inhibition of behaviour change (move to warm environment)
What are the non electrical ways to measure temp ? Need to know and how to draw graphs
Liquid Expansion Thermometers
These relatively simple devices rely on a substance that expands with increased temperature, which is calibrated to a scale. A prime example of this is the humble mercury thermometer.
The advantage is clear – they are cheap, readily available, and easy to use. However, the inherent risk of a toxic substance such as mercury is less than ideal, and they have a slow response time.
Gas Expansion Thermometers
These devices use an aneroid gauge, which is a fancy term for a gauge without liquid.
As the gas within the gauge is heated, the kinetic energy within the molecules increase. As the volume within the gas container is fixed, the gas molecules exert more pressure on the gauge, causing it to stretch and move along a dial calibrated for temperature.
While they are sensitive, they are also large, bulky and have a slow response time.
What are the stages of heat loss
https://teachmeanaesthetics.com/physics/heat-and-temperature/ has a diagram
Stages of Heat Loss
There are three stages of heat loss described in the literature:
1 – Redistribution: A sharp decline in body temperature due to vasodilation and movement of blood to the peripheries (redistribution from core) - first 1 hr
2 – Linear phase: A more gradual decline until a new set-point is reached, actual heat lost - next 2.5 hrs
3 – Equilibrium: Temperature is maintained at this new level
why is it important to measure temp?
Haematological: Impaired coagulation, impaired platelet function
Cardiac: Risk of arrhythmia
Pharmacological: Reduce rate of drug metabolism, reduced MAC
Metabolic: Shivering increases oxygen consumption
Renal: ‘Cold diuresis’ as an increase in central circulating volume, caused by vasoconstriction, increases the GFR
How do infra -red thermometers work?
Firstly, the ‘pyroelectric effect’ describes how some substances become temporarily charged when exposure to infrared radiation. Secondly, the wavelength and intensity of infrared radiation varies with temperature. - al objects give off infrared, higher temp = more infra red given off
Combined, this means that as temperature varies, the potential difference generated by pyroelectric crystals in the thermometer varies, and therefore temperature can be estimated.
Advantage of this technique include that the equipment is small, portable, readily available, and has a rapid response time.
A key disadvantage is that it relies on the infrared beam reaching the tympanic membrane, which can be affected by wax, abnormal anatomy, and a bad aim.
