1. Pressure
Week 3

2. Definition of Pressure
Defined as force (F) acting perpendicularly to a surface area (A)
P = F/A
In the atmosphere the gas we breathe (Nitrogen, Oxygen, Co2 and trace gases) are in constant motion, creating kinetic energy and FORCE applied against the surface of the earth. This is the atmospheric pressure

3. Atmospheric pressure
Atmospheric pressure is usually measured by the height of a liquid in a closed, evacuated tube as shown on pages in the text book.
You have already learned the normal values at sea level for one atmosphere in several different pressure scales.
At altitudes above sea level the atmospheric pressure is lower because there is less air pushing down on the surface.
At sea level, 1 ATM = 760 torr, In Denver, 1 mile above sea level, 1 ATM = 680 tor.

4. Atmospheric pressure units
At sea level:
760 mmHg
760 torr
1034 cmH2O
33 ft H2O
14.7 PSI
29.9 inHg
kPa
*in respiratory we will use mmhg/torr

5. Positive pressure
Pressure applied that is above the current atmospheric pressure
In respiratory we do this all the time with devices such as mechanical ventilators
We do this to overcomes a resistance or disruption in normal pressure gradients between the atmosphere and the patients lung

6. Negative pressure
"Negative" pressure is a gauge pressure that is below atmospheric pressure. Since atmospheric pressure measured in gauge pressure is 0, any gauge pressure that is below atmospheric pressure will be negative. It is very important to remember that if you are measuring pressure on an absolute scale, you can not have a pressure that is less than 0 or a negative number.
 Negative is also called vacuum pressure
We use Negative pressure when suctioning patients.
For example: a suction pressure of 60 mmHg is a vacuum, or 60 less that the current atmospheric pressure

7. The air is made up of molecules.

8. Gravity pulls the air molecules toward the earth, giving them weight
Gravity pulls the air molecules toward the earth, giving them weight. The weight of the air molecules all around us is called the air pressure.
Your weight is the result of gravity pulling your mass down on the bathroom scales. Note that weight has units of a force, such as pounds.
Your weight is the result of gravity pulling your mass down on the bathroom scales. Note that weight has units of a force, such as pounds.

9. High altitudes = lower pressure
Air pressure can be thought of as the column of air rising above us. As we go up in altitude, we get closer to the top of the column. Thus there are fewer molecules of air above us to be pulled down by gravity, so the air “weighs” less. Therefore, pressure always decreases as one goes up.
Low altitudes = higher pressure

10. Atmospheric pressure
Air pressure can be thought of as the column of air rising above us. As we go up in altitude, we get closer to the top of the column. Thus there are fewer molecules of air above us to be pulled down by gravity, so the air “weighs” less. Therefore, pressure always decreases as one goes up.

11. Atmospheric Pressure
Gas pressure depends on both density and temperature.
Adding air molecules increases the pressure in a balloon.
Heating the air also increases the pressure.

12. Air pressure is equal in all directions.
Because air is a fluid, force applied in one direction is distributed equally in all directions. Thus the downward pull of gravity on air molecules produces air pressure in all directions.
Because air is a fluid, force applied in one direction is distributed equally in all directions. Thus the downward pull of gravity on air molecules produces air pressure in all directions.
Pressure = force per unit area

13. Barometric pressure goes down.
As elevation goes up
Barometric pressure goes down.
This is an inverse relationship.

14. A Barometer
is used
to measure air pressure.

15. Torricelli’s barometer used a glass column suspended in a bowl of mercury. The pressure of the air molecules pushed the mercury up into the glass tube.
The weight of the mercury in the tube was equal to the weight of the air pressing down on the mercury in the dish.
The abbreviation “Hg” is the chemical symbol for mercury. Some kinds of pressure reading instruments, including some barometers, use the abbreviation “mmHg,” meaning “millimeters of mercury.” 760 mmHg is considered the standard “normal” atmospheric pressure at sea level. This unit is called a “torr,” after Torricelli.
To construct a mercury barometer, fill a tube with a liquid. Invert then tube in a dish of liquid holding your thumb over the top of the tube until the the tube is immersed in the bowl of liquid, the atmospheric pressure will keep the liquid in the tube from emptying such that the weight of the liquid in the tube equalize with the atmospheric pressures. (Do not do this with mercury because of its toxicity)
Mercury was used because it is a very heavy liquid, so the tube could be relatively short. The tube in a mercury barometer still has to be over a meter long. Students may want to try building a barometer using colored water. How high would the tube need to be? Merucy is about 11 times more dense than water. What if they used milk or some other liquid, would the height be the same?

16. As atmospheric pressure increases…
The mercury in the tube rises.

17. The Mercury Barometer Good: Bad: Simple to construct Highly accurate
Glass tube is fragile
Mercury is very toxic!
Although mercury has been used for hundreds of years, its toxic effects have only been fully realized in the last few decades. Students should NEVER handle mercury or broken mercury thermometers or barometers. Mercury should also never be thrown in the trash or washed down the drain, since it moves easily up the food chain from fish to humans. A local health department or environmental professional can assist with disposal of old or broken mercury instruments. GLOBE instrument specifications call for organic-fluid (non-mercury) or digital thermometers, except for the analog min/max thermometer, which is mounted in a shelter and is not handled by the students.
Although mercury has been used for hundreds of years, its toxic effects have only been fully realized in the last few decades. Students should NEVER handle mercury or broken mercury thermometers or barometers. Mercury should also never be thrown in the trash or washed down the drain, since it moves easily up the food chain from fish to humans.

18. The Aneroid Barometer No fragile tubes! No toxic chemicals!
No batteries!
Never needs winding!

19. An aneroid barometer uses a cell which has had most of the air removed.
MILLIBARS
As the air pressure around the cell increases, it presses on the cell, which causes the needle to move.
The word “aneroid” means “no air,” and refers to the partial vacuum inside the cell. The aneroid cell is shaped like a bellows, so that it can flex as air pressure changes. Increasing air pressure compresses the cell, causing the needle to register a change. Decreasing pressure allows the cell to expand, causing the needle to move in the opposite direction.
The use of inches of mercury is a hold-over from the days of mercury barometers. It refers to the actual height of mercury in the glass tube. Millibars are metric system units, and as such are readily understood by scientists around the world.
Television weather forecasters usually give barometric pressure in inches of mercury. However, meteorologists measure atmospheric pressure in millibars.

20. As we have noted earlier, higher elevations have fewer air molecules pressing downward, and so atmospheric pressure is lower. This means a barometer will read lower as it is carried to a higher elevation. Airplanes use a special type of barometer, called an altimeter, to measure altitude.

21. Most aneroid barometers have a needle which can be set to remember the previous reading.
Knowing how the air pressure is changing is as important as knowing the actual barometric reading. The set needle allows students to compare the current reading to the previous one. If the current reading is less than the previous one, the barometric pressure is falling. If the current reading is more than the previous one, the pressure is rising. If it is the same as the previous reading, the pressure is said to be steady. Weather forecasters often use the phrases “falling barometer,” “rising barometer,” or “steady barometer” as a way of referring to the change in atmospheric pressure.

22. Atmospheric Pressure
Although pressure varies with altitude, the concentration of gases do not change.
Meaning there is 21% O2 and 78% Nitrogen everywhere in the atmosphere.
The difference is the pressure. Less pressure= less pressure change from in the lung to the outside.
High altitudes = increased work of breathing

23. Changing Pressure A rising barometer = increasing air pressure.
This usually means:
Rising barometer readings indicate that a high pressure system is approaching. Higher atmospheric pressure is usually associated with fair weather and clearing skies.
Rising barometer readings indicate that a high pressure system is approaching. Higher atmospheric pressure is usually associated with fair weather and clearing skies.

24. Changing Pressure A falling barometer = decreasing air pressure.
This usually means:
Falling barometer readings usually indicate the approach of an area of low pressure. Low pressure readings are usually associated with storm systems. Tornadoes and hurricanes can produce very low barometric readings.
Falling barometer readings usually indicate the approach of an area of low pressure. Low pressure readings are usually associated with storm systems. Tornadoes and hurricanes can produce very low barometric readings.

25. Air Movement and Flow

26. Fluids (air and water) flow from areas of high pressure to areas of low pressure.
Change in pressure across a horizontal distance is a pressure gradient.
Greater the difference in pressure and the shorter the distance between them, the steeper the pressure gradient and the high the velocity of flow
In the lung, flow travels to the alveoli based on the diameter of the airway and also the pressure gradient. We will learn about this in another lecture
6-1

27. Pressure gradient in lung

31. speed, velocity, and flow.
Speed is a measurement of an object’s movement in units of distance or length /time, (ie cm/sec, miles per hour).
Velocity is the speed of an object with its direction at a given instant, (ie 50 miles/hour South).
Fluid flow is a special kind of velocity expressed in units of volume/time, ie ml/sec, l/min. Remember that a fluid is a substance capable of flowing ---a gas or liquid.

32. Kinetic Theory of Matter
The Kinetic Theory of Matter is the theory that all molecules are in constant motion resulting in kinetic energy. This theory applies to all three states of matter -- solids, liquids and gases.

33. States of Matter
Solids – have a high degree of internal order; their atoms have a strong mutual attractive force
Liquids – atoms exhibit less degree of mutual attraction compared with solids, they take the shape of their container, are difficult to compress, exhibit the phenomenon of flow
Gases – weak molecular attractive forces; gas molecules exhibit rapid, random motion with frequent collisions, gases are easily compressible, expand to fill their container, exhibit the phenomenon of flow

34. States of Matter Internal energy of matter
All matter possesses energy. There are 2 types of internal energy:
The energy of position, and the energy of motion.
Internal energy of matter
Potential energy (Position) The strong attractive forces between molecules that cause rigidity in solids
Kinetic energy (Motion) Gases have weak attractive forces that allow the molecules to move about more freely, interacting with other objects that they come in contact with
Internal energy and temperature
The two are closely related: internal energy can be increased by heating or by performing work on it.
Absolute zero = no kinetic energy

35. Physical properties of a solid:
Possess the least amount of KE
Mostly Potential Energy in intermolecular forces holding particles together
Can maintain their volume & shape

36. Physical properties of a liquid:
Intermolecular, cohesive forces are not as strong
They exhibit fluidity (particles sliding
They exhibit a buoyant force
Essentially incompressible
Assume the shape of their container

37. Physical properties of a gas:
Extremely weak – if any – cohesive forces
Possess the greatest amount of KE & the least amount of Potential Energy
Motion of atoms & molecules is random
Do not maintain their shapes & volumes but expand to fill the available space
Exhibit the phenomenon of flow
Exhibits the least thermal conductivity
Uses: Gas therapy (Oxygen, Heliox, Nitrous oxide…HHN/SVN…)

38. Change of State Liquid-solid phase changes (melting and freezing)
Melting = changeover from the solid to the liquid state
Melting point = the temperature at which melting occur.
Freezing = the opposite of melting
Freezing point = the temperature at which the substance freezes; same as its melting point

39. Change of State (cont.) Properties of liquids
Pressure – depends on the height and weight density.
Buoyancy – occurs because the pressure below a submerged object always exceeds the pressure above it
Viscosity – the force opposing a fluid’s flow. The greater the viscosity of a fluid, the greater the resistance to flow.
Blood has a viscosity five times greater than that of water

40. Change of State (cont.) Heat transfer
Conduction – transfers heat in solids
Convection – transfers heat in liquids and gases
(Example: heating homes or infant incubators)
Radiation – occurs without direct contact between two substances - example: microwave oven
Evaporation/Condensation: requires heat energy to occur
Sublimation - change from a solid to a gas without an intermediate change to a liquid - example dry ice turning into CO2

41. Heat Transfer Conduction: https://www.youtube.com/watch?v=9joLYfayee8
Convection
Radiation iQ
Condensation/evaporation
eature=related

42. Change of State (cont.)
Pascal’s Principle. Liquid pressure depends only on the height and weight density of the liquid and not the shape of the vessel or total volume of a liquid.

43. Pascal's law
Pascal's law states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same.
Pascal’s Law states that when you apply pressure to confined fluids (contained in a flexible yet leak-proof enclosure so that it can’t flow out), the fluids will then transmit that same pressure in all directions within the container, at the same rate. The simplest instance of this is stepping on a balloon; the balloon bulges out on all sides under the foot and not just on one side. This is precisely what Pascal’s Law is all about – the air which is the fluid in this case, was confined by the balloon, and you applied pressure with your foot causing it to get displaced uniformly.

44. Change of State (cont.) Cohesion and adhesion
The attractive force between like molecules is cohesion.
The attractive force between unlike molecules is adhesion.
The shape of the meniscus depends on the relative strengths of adhesion and cohesion.
H20: Adhesion > Cohesion
Mercury: Cohesion > Adhesion
Mercury
H20

45. Cohesion and Adhesion
Cohesion: Water is attracted to water Adhesion: Water is attracted to other substances
Adhesion and cohesion are water properties that affect every water molecule on earth and also the interaction of water molecules with molecules of other substances. Essentially, cohesion and adhesion are the "stickiness" that water molecules have for each other and for other substances.
The water drop is composed of water molecules that like to stick together, an example of the property of cohesion. The water drop is stuck to the end of the pine needles, which is an example of the property of adhesion. Notice I also threw in the all-important property of gravity, which is causing the water drops to roll along the pine needle, attempting to fall downwards. It is lucky for the drops that adhesion is holding them, at least for now, to the pine needle.

46. Change of State (cont.) Liquid to vapor phase changes
Boiling – heating a liquid to a temperature at which its vapor pressure equals atmospheric pressure.
Saturation – equilibrium condition in which a gas holds all the water vapor molecules that it can.
Dew point – temperature at which the water vapor in a gas begins to condense back into a liquid.
Evaporation – when water enters its gaseous state at a temperature below its boiling point.

47. The Gas Law
Ideal Gas follows kinetic molecular theory, made up of large number of molecules that are in rapid random motion following perfect elastic collitions losing no momentum
How the Kinetic Molecular Theory Explains the Gas Laws
The pressure of a gas results from collisions between the gas particles and the walls of the container.
Each time a gas particle hits the wall, it exerts a force on the wall.
An increase in the number of gas particles in the container increases the frequency of collisions with the walls and therefore the pressure of the gas.
Avogadro's Hypothesis
As the number of gas particles increases, the frequency of collisions with the walls of the container must increase.
This, in turn, leads to an increase in the pressure of the gas.
Flexible containers, such as a balloon, will expand until the pressure of the gas inside the balloon once again balances the pressure of the gas outside.
Thus, the volume of the gas is proportional to the number of gas particles.

48. The Gas Laws Charles Law Boyle’s Law
The volume of a gas increased with the temperature
The volume of a given amount of dry ideal gas is directly proportional to the Kelvin Temperature provided the amount of gas and the pressure remain fixed.
When we plot the Volume of a gas against the Kelvin temperature it forms a straight line.
V1 / T1 = V2 / T2
Boyle’s Law
the product of the pressure and volume are observed to be nearly constant.
The product of pressure and volume is exactly a constant for an ideal gas.
p * V = constant

50. WATER VAPOR

51. (9.8oC)