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MED 101- PHYSICS I > 13. CHARACTERISTIC PRESSURES IN THE BODY (PART 1) > Flashcards

13. CHARACTERISTIC PRESSURES IN THE BODY (PART 1) Flashcards

1
Q
  1. Pressures are a very common phenomenon in our lives. What are some examples of pressures?
A
  • Atmospheric Pressure
  • Tire Pressure
  • Blood Pressure
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2
Q
  1. In which states is Pressure used for?
A
  • gases
  • liquid
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3
Q
  1. What is the quantity force per unit area for solids called?
A
  • stress
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4
Q
  1. What is the definition for Pressure?
A
  • the force per unit area
    (in a gas or a liquid)
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5
Q
  1. In which unit is pressure measured?
A
  • it is measured in Newton’s per square metres
    (Pascals)
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6
Q
  1. What is the standard Atmospheric pressure at Sea Level?
A
  • 101kPa
    (760 mm Hg)
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7
Q
  1. What is a common method of indicating pressure in medicine?
A
  • by looking at the height of a column of Mercury
    (mm Hg)
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8
Q
  1. What is 1mmHg equal to in kPa?
A
  • 0.133kPa
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9
Q
  1. What are the two broad categories that materials are classified as?
A
  • solids
  • fluids
    (gases and liquids)
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10
Q
  1. What are the distinguishing features between gases, solids and liquids?
A
  • differences at their molecular levels
  • differences at their macroscopic levels
  • differences at their cosmic levels
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11
Q
  1. What is a fluid?
A
  • a substance that is either in liquid or gas phase
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12
Q
  1. How do fluids react to deformation?
A
  • a fluid deforms continuously under the influence of a sheer stress
  • a fluid never stops deforming
  • instead: it reaches a constant rate of strain
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13
Q
  1. What can be said about the Deformation occurring in this picture.
A
  • this picture shows the deformation of a rubber block placed between two parallel plates
  • it is experiencing the influence of shear force
  • the shear force shown is acting in the rubber
  • there is also an equal shear stress/force of opposite direction acting on the upper plate
  • the stretch is acting in one direction
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14
Q
  1. How does a solid resist an applied shear stress?
A
  • it deforms
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15
Q
  1. In solids, what is proportional to the strain?
A
  • the stress
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16
Q
  1. In fluids, what is the stress proportional to?
A
  • the strain rate
17
Q
  1. How does a solid react to a constant shear force being applied to it?
A
  • the solid will eventually stop deforming
  • it will do this at a fixed strain angle
18
Q
  1. What is the definition of stress?
A
  • it is the force per unit area
19
Q
  1. What is a Normal Stress?
A
  • this is the normal component of a force acting on a surface per unit area
  • it is associated with pressure
20
Q
  1. What is Shear Stress?
A
  • it is the tangential component of a force acting on a surface per unit area
  • it is always written as Force per unit

TANGENTIAL= along a tangent
TANGENT= a straight line that touches a curve or a
curved surface at a point

21
Q
  1. What is Pressure?
A
  • the normal stress in a fluid at rest
22
Q
  1. What is meant by Zero shear stress?
A
  • a fluid at rest is at a state of zero shear stress
23
Q
  1. What develops in a liquid when the liquid is tilted, or the container walls that the liquid was in are removed?
A
  • a shear develops
  • it does this as the liquid moves to re-establish a
    horizontal free surface
24
Q
  1. What can be said about the shear stress and the pressure for fluids at rest?
A
  • the shear stress is zero
  • the pressure is the only normal stress
25
Q
  1. How do we mathematically work out Normal Stress?
A
26
Q
  1. How do we mathematically work out Shear Stress?
A
27
Q
  1. How would we describe the molecular structure of a liquid?
A
  • the molecules can move relative to each other
  • the volume remains relatively constant
  • this is because of the strong cohesive forces between the molecules
  • the liquid takes the shape of the container it is in
  • it forms a free surface in a larger container that is in a gravitational field
  • molecules in a liquid can rotate
  • they can translate freely
  • they have weaker intermolecular bonds than solids
  • they have stronger intermolecular bonds than liquids
  • they have flexibility between the bonds of the
    molecules
  • there is enough intermolecular force to still keep the
    molecules together
28
Q
  1. How would we describe the molecular structure of a gas?
A
  • a gas expands until it encounters the walls of the container
  • it fills up the entire available space
  • this is because the gas molecules are widely spaced
  • the cohesive forces between the molecules are very small
  • a gas in an open container CANNOT form a free surface
  • molecules are far apart from each other
  • there is no existent molecular ordering
  • the molecules have Brownian motion
  • they have random, unorganised motion
  • the intermolecular bonds between gas molecules are the weakest
29
Q
  1. What can be said about the molecular arrangement of Solids?
A
  • molecules are arranged in a pattern
  • this pattern is repeated throughout the solid
30
Q
  1. What is the single most important difference between fluids and solids?
A
  • a fluid must assume the shape of the container in which it is placed
  • a solid is able to sustain its own shape
31
Q
  1. How does a body fluid respond when a shearing force is exerted on it?
A
  • it is not able to resist the shearing force
  • it must keep deforming when it is subjected to this force

EG: the motion in the water in a lake is caused by an
overpassing wind
: it cannot resist the wind
: it can only keep deforming

32
Q
  1. What causes the difference between fluids and solids?
A
  • the intensity of the forces holding the molecules together
  • this forces form a coherent piece of material
33
Q
  1. Can fluids be transformed into solids?
A
  • yes
  • and vice versa
  • this is done by heating
  • or by changing the pressure of the ambient environment
34
Q
  1. How is the pressure of a fluid column mathematically worked out?
A
  • P= p.g.h
  • P= pressure in a liquid column
  • p = the fluid density
  • g = gravitational constant
  • h = height of the column
35
Q
  1. What are the densities of the following fluids:

35.1: Mercury
35.2: Water
35.3: Blood Plasma
35.4: Circulating blood cells
35.5: Whole blood

A

35.1: 13 560 kg/m³

35.2: 1000 kg/m³

35.3: 1025 kg/m³

35.4: 1125 kg/m³

35.5: 1060 kg/m³

36
Q
  1. What is Absolute Pressure (Pabs) ?
A
  • it is the total force per unit area
37
Q
  1. What is commonly cited when referring to pressures of the body?
A
  • the Gauge Pressure
    (Pgauge)
  • the pressure relative to a standard
  • the standard in this case is atmospheric pressure
38
Q
  1. How is Pgauge mathematically calculated?
A
  • Pgauge = Pabs - 1 atm
    (atmospheric pressure)
39
Q
  1. When we discuss blood pressure and the pressure of the lungs, what does the term P refer to?
A
  • it refers to the gauge pressure relative to the local atmospheric pressure

MED 101- PHYSICS I (28 decks)

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