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Physics and Math Correct Deck > Ch. 4: Fluids > Flashcards

Ch. 4: Fluids Flashcards

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1
Q

defn: fluids

A

characterized by their ability to flow and conform to the shapes of their containers (liquids and gases)

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2
Q

defn: solids

A

do not flow, are rigid enough to retain a shape independent of their containers

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3
Q

aka: tangential forces

A

shear forces (only withstood by solids)

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4
Q

defn + scalar or vector: density

A

ratio of mass to volume

scalar quantity –> has no direction

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5
Q

what is a milliliter equivalent to?

A

a cubic centimeter

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6
Q

how many liters are in a cubic meter?

A

1000!

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7
Q

defn + unit: specific gravity

A

the density of a fluid as compared to that of pure water at 1 atm and 4 deg C

unitless

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8
Q

what can specific gravity be used as?

A

a tool for determining if an object will sink or folat in water

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9
Q

defn + SI unit + scalar v. vector: pressure

A

a ratio of the force per unit area

SI unit: pascal (Pa)

scalar, magnitude but no direction

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10
Q

what are 3 commonly used units of pressure other than Pa?

A

mmHg
torr
atm

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11
Q

why is pressure a scalar and not a vector?

A

place a surface inside a closed container filled with gas

the individual molecules will exert pressure that is the same at all points within the container

pressure applies in all directions at any point

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12
Q

is atmospheric pressure the same everywhere in the world?

A

no! it changes with altitude

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13
Q

defn + aka: absolute pressure

A

aka: hydrostatic pressure

the total pressure that is exerted on an object that is submerged in a fluid

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14
Q

defn + aka: incident pressure

A

aka: ambient pressure

the pressure at the surface of a fluid

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15
Q

defn: gauge pressure

A

the difference between the absolute pressure inside the tire and the atmospheric pressure outside the tire

AKA

the amount of pressure in a closed space above and beyond atmospheric pressure

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16
Q

defn: hydrostatics

A

the study of fluids at rest and the forces and pressures associated with standing fluids

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17
Q

defn: incompressible fluid

A

fluids with volumes that cannot be reduced by any significant degree through application of pressure

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18
Q

defn: Pascal’s principle

A

for incompressible fluids, a change in pressure will be transmitted undiminished to every portion of the fluid and to the walls of the containing vessel

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19
Q

defn: hydraulic systems

A

systems that take advantage of the near-incompressibility of liquids to generate mechanical advantage

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20
Q

how do hydraulic systems generate output force?

A

by magnifying an input force by a factor equal to the ratio of the cross-sectional area of the larger piston to that of the smaller piston

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21
Q

are the volumes of fluid displaced by piston 1 and piston 2 equal or different in a hydraulic system?

A

equal!

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22
Q

defn + layman’s: Archimedes’ principle

A

a body wholly or partially immersed in a fluid will be buoyed upwards by a force equal to the weight of the fluid that it displaces

in layman’s terms: any object placed in a fluid will cause a volume of fluid to be displaced equal to the volume of the object that is submerged

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23
Q

how can we visualize the buoyant force?

A

it is the force of the liquid trying to return to the space from which it was displaced, thus trying to push the object up and out of the water

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24
Q

is the buoyant force due to the liquid or the object?

A

the liquid!

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25
Q

will an object float no matter what it is made of and its mass if its average density is less than or equal to the density off the fluid into which it is placed?

A

yes!

26
Q

talk about objects being submerged in relation to the specific gravity of water

A

if we express the object’s specific gravity as a percent, this directly indicates the percent of the object’s volume that is submerged (when the fluid is pure water)

object SG < or = 1 –> object floats
object SG > 1 –> object will sink

object SG = 1 –> 100% of the object will be submerged but it will not sink

27
Q

effect: surface tension

A

causes the liquid to form a thin but strong layer like a “skin” at the liquid’s surface

28
Q

defn: cohesion

A

the attractive force that a molecule of liquid feels toward other molecules of the same liquid

the force behind surface tension

29
Q

explain the process of surface tension in terms of the intermolecular forces between the separate molecules of liquid water and how it differs for molecules below the surface and molecules on the surface

A

molecules below the surface: there are attractive intermolecular forces coming from all sides (they balance out)

molecules on the surface: molecules only have these strong attractive forces from the molecules below them –> pulls the surface of the liquid toward the center –> establishes tension in the plane of the surface of the water

when there is an indentation on the surface (like a bug’s foot), then the cohesion can lead to a net upward force

30
Q

defn: adhesion

A

the attractive force that a molecule of liquid feels toward the molecules of some other substance

31
Q

defn: meniscus

+ why does it form

A

a curved surface in which the liquid “crawls” up the side of the container a small amount

forms when the adhesive forces are greater than the cohesive forces

32
Q

defn + why does it form: backwards (convex) meniscus

A

meniscus with the liquid level higher in the middle than at the edges

occurs when the cohesive forces are greater than the adhesive forces

33
Q

defn: fluid dynamics

A

the study of fluids in motion

34
Q

defn: viscosity

A

the resistance of a fluid to flow

35
Q

defn: viscous drag

A

a nonconservative force that is analogous to air resistance

increases with increased viscosity of a fluid

36
Q

defn: inviscid

A

ideal fluids with no viscosity

37
Q

defn: laminar flow

A

smooth, orderly

modeled as layers of fluid that flow parallel to each other (the layers will not necessarily have the same linear speed)

38
Q

defn: Poiseuille’s law

A

a way to calculate the rate of laminar flow through a pipe or confined space

39
Q

what is the relationship between the radius and pressure gradient of laminar flow through a pipe or confined space as described by Poiseuille’s law

what does this translate to tangibly

A

inverse exponential to the fourth power

even a very slight change in the radius of the tube has a significant effect on the pressure gradient assuming a constant flow rate

40
Q

defn: turbulent flow

A

rough, disorderly

causes the formation of eddies

41
Q

defn: eddy

A

swirls of fluid of varying sizes occuring typically on the downstream side of an obstacle

42
Q

when can turbulence arise in unobstructed fluid flow?

A

when the speed of the fluid exceeds a certain critical speed which depends on the physical properties of the fluid

43
Q

defn: boundary layer

A

the thin layer of fluid adjacent to the wall where laminar flow occurs even when the rest of the fluid has complex flow patterns due to the critical speed of the fluid being exceeded

44
Q

defn: Reynolds number

A

a dimensionless constant that depends on factors such as the size, shape, and surface roughness of any objects within the fluid

45
Q

defn: streamlines

A

indicate the pathways followed by tiny fluid elements as they move

46
Q

what is the relationship between the velocity vector of a fluid particle and the streamline?

A

the velocity vector of a fluid particle will always be tangential to the streamline at any point

47
Q

do streamlines cross each other?

A

no, never!

48
Q

defn + char for closed system: flow rate

A

volume per unit time

constant, independent of changes in cross-sectional area

49
Q

defn: linear speed

A

a measure of the linear displacement of fluid particles in a given amount of time

50
Q

does linear speed change relative to cross-sectional area?

A

yes!

51
Q

impact: continuity equation

A

tells us that fluids will flow more quickly through narrow passages and more slowly through wider ones

52
Q

what are the two principles of conservation that lead to Bernoulli’s equation?

A
  1. continuity equation arises from the conservation of mass of fluids –> for a constant flow rate, there is an inverse relationship between the linear speed of the fluid and the cross-sectional area of the tube: fluids have higher speeds through narrower tubes
  2. fluids that have low viscosity and demonstrate laminar flow can also be approximated to be conservative systems
53
Q

defn: dynamic pressure

A

the pressure associated with the movement of a fluid (essentially the kinetic energy of the fluid divided by the volume)

54
Q

defn: term pgh of Bernoulli;s equation

A

the pressure associated with the mass of fluid sitting above some position

55
Q

defn: energy density

A

a ratio of energy per cubic meter

essentially pressure

56
Q

defn: static pressure

A

essentially absolute pressure

57
Q

defn: Bernoulli’s equation

+ defn in terms of energy conservation

A

the sum of the static pressure and the dynamic pressure will be constant within a closed container for an incompressible fluid not experiencing viscous drag

energy conservation: more energy dedicated toward fluid movement means less energy dedicated toward static fluid pressure (and less movement means more static pressure)

58
Q

defn: pitot tube

A

specialized measurement devices that determine the speed of fluid flow by determining the difference between the static and dynamic pressure of the fluid at given points along the tube

59
Q

defn: Venturi effect

A

as the tube narrows, the linear speed increases

thus, the pressure exerted on the walls decreases, causing the column above the tube to have a lower height at this point

60
Q

describe the circulatory system in terms of fluid dynamics

A

it is a closed loop that has a nonconstant flow rate

61
Q

defn: pulse

A

the feeling and measurement of the nonconstant flow rate of the circulatory system

Physics and Math Correct Deck (12 decks)

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