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Fluid Mechanics > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

Give the two conditions that qualify as a “static situation” in FM.

A
  1. The fluid is at rest.
  2. The fluid is moving in such a manner that there is no relative motion between adjacent particles.

Ref: Pg 31

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2
Q

True or False

In a static situation, there will be no shearing stresses in the fluid.

A

True

Ref: Pg 31

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3
Q

True or False

In a static situation, the only forces that develop on the surfaces of the particles are due to viscous forces.

A

False
In a static situation, the only forces that develop on the surfaces of the particles are due to pressure forces.

Ref: Pg 31

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4
Q

True or False
If a closed volume of fluid moves as a rigid body, with no relative motion between particles, the “no shearing stress” assumption is still valid for static analysis.

A

True

Ref: Pg 31

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5
Q

True or False

Assuming that there is no shearing, the pressure in a fluid at rest or in motion is independent of direction.

A

True

Ref: Pg 32

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6
Q

Give the definition for Pascals Law.

A

The pressure at a point in a fluid at rest or in motion is independent of direction as long as there are no shearing stresses present.

Ref: Pg 32

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7
Q

Consider an infinitesimal fluid element subject taken from a static fluid mass. What two forces act on the element and what generates those two forces?

A

Surface Forces: Generated due to the pressure on the element.
Body Forces: Due to gravity. Equal to the weight of the element.

Ref: Pg 33

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8
Q

True or False

The pressure will NEVER vary across a fluid particle.

A

False, pressure can vary across a fluid element.

Ref: Pg 33

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9
Q

Assuming no shearing is present, the resultant force acting on a small fluid element depends only on ______.

A

The pressure gradient.

Ref: Pg 33

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10
Q

For liquids or gasses at rest, the pressure gradient in the vertical direction at any point in a fluid depends only on_______ of the fluid at that point.

A

The specific weight.

Ref: Pg 34

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11
Q

What is the definition of an “incompressible fluid?”

A

A fluid with constant density.

Ref: Pg 35

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12
Q

True or False

For liquids, the variation of density is usually large, even for small changes in pressure.

A

False
Generally, for liquids, the variation of density is negligible even for large changes in pressure.

Ref: Pg 35

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13
Q

What is a “hydrostatic distribution?”

A

A hydrostatic pressure distribution is encountered in fluids when the pressure increases linearly with depth.

Ref: Pg 35

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14
Q

What is the physical interpretation of a hydrostatic “pressure head?”

A

A pressure head is interpreted as the height of a column of fluid of specific weight (gamma) required to give a pressure difference p1 - p2.

Extra Note: For example, a pressure of 10 psi can be specified in terms of a pressure head as 23.1 feet of water.

Ref: Pg 36

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15
Q

What is typically chosen as the reference plane in hydrostatic analysis?

A

The free surface.

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16
Q

True or False
The pressure in a homogeneous, incompressible fluid at rest depends only on the depth of the fluid relative to some reference plane and it is NOT influenced by the size or shape of the container in which it is held.

A

True

Ref: Pg 36

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17
Q

What is the principle on which many hydraulic devices are designed?

A

The transmission of pressure through a stationary fluid.

Ref: Pg 37

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18
Q

For a hydraulic actuator with input area A1 and output area A2, what is the relationship between input and output force?

A

F2 = (A2/A1)(F1)
where A2 > A1

Ref: Pg 37

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19
Q

True or False

The specific weights of common gases are small when compared with those of liquids.

A

True

Ref: Pg 37/38

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20
Q

True or False
Since the specific weights of gasses are comparatively large, it follows from Eq 2.4 in the book that the pressure gradient in the vertical direction is correspondingly large.

A

False
Since the specific weights of gasses are comparatively SMALL, it follows from Eq 2.4 in the book that the pressure gradient in the vertical direction is correspondingly SMALL.

Ref: Pg 38

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21
Q

True or False
Typically, due to the specific weights of gasses, the pressure gradient in the vertical direction is small even over distances of several hundred feet the pressure will remain practically constant.

A

True

Ref: Pg 38

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22
Q

True or False
If the specific weight of a fluid varies significantly as we move from point to point, the pressure will no longer vary linearly with depth.

A

True

Ref: Pg 38

23
Q

If the temperature is constant throughout an elevation change, the conditions are termed ______.

A

Isothermal

Ref: Pg 38

24
Q

Absolute pressure is measured relative to ____.

A

A perfect vacuum.

Ref: Pg 41

25
Q

Gauge pressure is measured relative to _____.

A

Local atmospheric pressure.

Ref: Pg 41

26
Q

True or False

A gauge pressure of zero corresponds to local atmospheric pressure.

A

True

Ref: Pg 41

27
Q

True or False

Absolute pressures are always positive.

A

True

Ref: pg 41

28
Q

True or False

Gauge pressures can never be negative.

A

False. Gauge pressures can be either positive or negative depending on whether the pressure is above atmospheric pressure (positive value) or below atmospheric pressure (a negative value).

Ref: Pg 41

29
Q

Vacuum pressure coresponds to ______.

A

Negative gauge pressure.

Ref Pg 41

30
Q

True or False

Manometers use vertical or inclined liquid columns to measure pressure.

A

True

Ref: Pg 43

31
Q

What is the fundamental equation for describing a manometer’s function?

A

p = (specific weight)(depth) + (initial pressure)

Ref: Pg 43

32
Q

What is the simplest type of monometer?

A

The piezometer tube.

Ref: pg 43

33
Q

True or False

A gauge fluid in a U-Tube manometer has a higher specific weight than the fluid in the container.

A

True

Ref: pg 44

34
Q

Give the manometer equation rules.

A
  1. Write the pressure at either end of the manometer.
  2. Proceed through the manometer, adding (gamma)(h) if moving to a greater depth or subtracting (gamma)(h) if moving to a lesser depth.
  3. Stop at the far end, or any point in between, and set the expression equal to the local pressure.

Ref: Pg 44

35
Q

True or False

The contribution of gas columns in manometers is usually negligible since the weight of the gas is so small.

A

True

Ref: Pg 44

36
Q

True or False
In a U-Tube manometer, increasing the density of the gauge fluid allows practical measurement of much larger pressures but sacrifices resolution.

A

True

Ref: pg 44

37
Q

True or False
In a U-Tube manometer, decreasing the density of the gauge fluid allows measurement of larger pressures but at the expense of resolution.

A

False. Decreasing the density of the gauge fluid limits the practical range of pressure measurement but increases the resolution.

Ref: Pg 44

38
Q

If small pressure changes need to be measured, which equipment would be better suited?

  1. U-Tube manometer
  2. Inclined Tube Manometer
A

2

Ref: Pg 46

39
Q

True or False

When an object is submerged, the force due to pressure is perpendicular to the surface of the object.

A

True

Ref: Pg 50

40
Q

The resultant force of a static fluid on a plane surface is due to ____________.

A

Thy hydrostatic pressure distribution on the surface.

Ref: Pg 50

41
Q

The magnitude of the resultant force on an object submerged in a static fluid depends on what factors?

A

The depth and is equal to the pressure (h*specific weight) acting at the centroid of the area multiplied by the total area.

Ref: Pg 51

42
Q

True or False

The resultant force on a submerged object in a stationary fluid acts through the centroid of the object.

A

False, the resultant force acts through the center of pressure.

Ref: Pg 52

43
Q

Ture or False

The center of pressure is located lower than the centroid for a body submerged in a stationary fluid.

A

True

Ref: Class lecture notes

44
Q

With respect to pressure prisms, the magnitude of the resultant static force on a submerged object is equal to ____.

A

The volume of the pressure prism.

Ref: Pg 56

45
Q

True or False

The resultant hydrostatic force passes through the centroid of the pressure prism.

A

True

Ref: Pg 56

46
Q

What is the equation for the buoyant force?

A

Fb = (Specific weight)(volume)

Ref: Pg 61

47
Q

What is the physical interpretation of the magnitude of the buoyant force?

A

The buoyant force has a magnitude equal to the weight of the fluid displaced by the body and is directed vertically upward. This is commonly referred to as Archimedes’ principle.

Ref: Pg 62

48
Q

True or False

The buoyant force passes through the CG of the displaced volume.

A

False. The buoyant force passes through the centroid of the displaced fluid volume.

Ref: Pg 62

49
Q

The point through which the buoyant force acts is called ________.

A

The center of buoyancy.

Ref: Pg 62

50
Q

True or False

Buoyancy effects can also be seen within fluids alone, as long as a density difference exists?

A

True

Ref: Pg 64

51
Q

Define “stable equilibrium” with respect to FM.

A

If the body is displaced, it will return to its equilibrium position.

Ref: Pg 64

52
Q

True or False
As long as the center of gravity is below the center of buoyancy, the body will be in stable equilibrium with respect to small rotations.

A

True

Ref: Pg 64

53
Q

True or False
A completely submerged body with its center of gravity above its center of buoyancy is in an unstable equilibrium position.

A

True

Ref: Pg 65

54
Q

True or False

The pressure distribution in a fluid mass that is accelerating along a straight path is hydrostatic?

A

False, it is NOT hydrostatic.

Ref: Pg 67

Fluid Mechanics (7 decks)

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