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PHSI > Module 2: Solids & Fluids > Flashcards

Module 2: Solids & Fluids Flashcards

1
Q

Describe molecule movement in solids (3)

A

Molecules oscillate about fixed centres

Vibration is small

Fixed centres form a repeated spacial pattern (long-range order)

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2
Q

Describe movement of molecules in liquids (5)

A

Centres of molecules are free to move

Material take shape if container

Intermolecular distances are slightly larger than solids

Amplitudes of vibration are slightly larger than solids

Regularity of structure is shown only between close molecules (short-range order)

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3
Q

Describe the movement of gas molecules (4)

A

Great kinetic energy

Widely separated

Experience small attractive forces

Move in straight lines until they collide

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4
Q

When is an object said to behave elastically/ be elastic?

A

When it returns to its original shape after being subjected to equal and opposite forces which change its size/ shape

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5
Q

Stress = ?

A

F/A

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6
Q

Units of stress

A

N m^-2 or Pascal Pa

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7
Q

Describe stress

A

The effect of a force’s uniform distribution over an object

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8
Q

Describe strain

A

The relative response of a material to stress

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9
Q

Tensile strain =

A

ΔL/L(subscript o)

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10
Q

Units of strain

A

No units

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11
Q

Young’s modulus

A

Stress over strain

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12
Q

Units of Young’s modulus

A

Nm^-2 / Pa

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13
Q

What does and does not determine Young’s modulus?

A

Depends on material of object

Does not depend on size, shape or volume

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14
Q

What is Young’s modulus a measure of? What does a higher Young’s modulus mean?

A

Stretchiness

A higher Young’s modulus means the material is less elastic

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15
Q

Shear strain

A

Deformation by slippage across a plane parallel to imposed stress

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16
Q

Symbol for shear modulus

A

S (or G)

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17
Q

Symbol for young’s modulus

A

γ

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18
Q

Symbol for bulk modulus

A

B

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19
Q

When does bulk strain occur?

A

When a volume is subject to an increase in pressure, it experiences a change in volume/ volume strain/ bulk strain

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20
Q

Why is bulk modulus negative?

A

The volume shrinks

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21
Q

Describe a stress-strain curve for a ductile material

A

Steep gradient for elastic area: minimal change in strain for a large amount of stress

Fracture occurs shortly after the elastic area stops

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22
Q

Describe the stress-strain curve for a soft tissue

A

Strain increase dramatically per increase in stress

J shaped curve

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23
Q

ρ = ?

A

ρ = mv

Density

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24
Q

Units for density

A

kg cm^-3

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25
Q

Pressure

A

A kind of stress that acts in all directions

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26
Q

How does atmospheric pressure arise?

A

The motion of molecules in the atmosphere exerts a force on the body

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27
Q

P = ?

A

P = F/A

Pressure

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28
Q

How does fluid exert its pressure across its volume? (3)

A

Equally in all directions

Acts perpendicular to the surface in contact with it

The same at equal depths in a container, regardless of shape

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29
Q

How can the volume of a liquid be changed?

A

By applying pressure

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30
Q

What does the equation describe:

P2-P1 = -pg (y2-y1)

A

Difference in pressure at two different points

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31
Q

Absolute pressure

A

Pressure relative to a vacuum

Atmospheric pressure + any extra

32
Q

Gauge pressure

A

Measured relative to atmospheric pressure

Only any extra pressure

33
Q

Minimum absolute pressure?

A

0 Pa

34
Q

How to calculate gauge pressure?

A

Subtract atmospheric pressure from total pressure

35
Q

How to calculate absolute pressure?

A

Add atmospheric pressure and gauge pressure

36
Q

Manometer

A

Device which measures gauge pressure

37
Q

What does gauge pressure depend on?

A

Density of fluid
Gravitational acceleration
Height

38
Q

Archimedes principle (object in fluid)

A

When a body is immersed in a fluid, the fluid exerts an upward force on the body which is equal to the weight of fluid displaced by the body

Basically, buoyant force = weight of displaced fluid

39
Q

When does a body come to rest in a fluid, and what is this state called?

A

When the weight of the body = buoyant force

(mg = pVg)
- p refers to density of fluid

Equilibrium

40
Q

When will a body sink in a liquid?

A

When it’s weight force is larger than the buoyant force

41
Q

Cohesion

A

Attraction between like substances

42
Q

Adhesion

A

Attraction between unlike substances

43
Q

Because there are attractive forces between liquid molecules, ______?

A

A net force pulls at the molecules at the top of the liquid (surface tension)

44
Q

How does surface tension act on surface area of bubbles and balloons?

A

Minimises it

A sphere gives the smallest surface area possible for a volume

45
Q

The smaller the bubble, the ______ the pressure

A

Larger

46
Q

Do molecules move to where pressure is lowest or highest? What does this mean for bubbles?

A

Lowest

Small bubbles get smaller (molecules move inwards)
Large bubbles get larger (molecules move outwards)

47
Q

In a bubble, what is the equation for pressure?

A

P = 4γ / r

γ = surface tension

48
Q

Capillarity

A

Balance between cohesive and adhesive (between liquid and small pore or tube) forces

49
Q

How do we achieve a negative meniscus?

A

Adhesive forces outweighs cohesive forces

50
Q

How do we achieve a positive meniscus?

A

Cohesive forces outweigh adhesive forces

51
Q

Incompressible fluid

A

A fluid which has constant density throughout

52
Q

Viscosity

A

Internal friction in the fluid

53
Q

Laminar flow, and what fluid characteristic does it suggest?

A

Layers of fluid slide smoothly past each other in a steady state pattern.

Usually fluids have lower viscosities like honey

54
Q

Turbulent flow, and when does it occur?

A

Irregular complex flow with mixing and eddies- no pattern

Occurs at high velocities or when there is a large change in velocity

55
Q

Equation of continuity

A

Mass flowing in = mass flowing out

A1v1 = A2v2

56
Q

What condition must the fluid fulfil for the equation of continuity to be correct?

A

Must be incompressible (constant fluid density)

57
Q

What is the term for Av in a fluid?

A

Flow rate

58
Q

Bernoulli’s equation (pressure in a fluid)

A

Pressure + kinetic energy + potential energy is constant at every point in a fluid

P + 0.5pv^2 + pgh = constant

(Where p = density of fluid)

59
Q

Streamline

A

A line whose tangent- at every point - is in the direction of fluid velocity

60
Q

What happens in places where streamlines converge?

A

Velocity increases

61
Q

In a pipe, how do particles in the middle, and particles at the sides differ? What can we conclude from this?

A

Particles in contact with the pipe have lower velocity

The particles in the centre have the highest velocity, and they drag the other particles along

Velocity is dependant on distance from the wall of the pipe

62
Q

η (liquids)

A

Viscosity

63
Q

Stress over rate of strain = ?

A

Viscosity

64
Q

Equation for η

A

η = (F/A) / (v/L)

65
Q

Which requires more force to move: a low or high viscosity fluid?

A

High viscosity

66
Q

Units for η viscosity

A

N s m^-2

67
Q

Fluid flows from ____ to ____ pressure

A

High to low

68
Q

What increases volume flow rate?

A

A higher difference in pressure between two points

69
Q

What resists laminar flow?

A

Friction within the fluid

and friction between the fluid and container walls

70
Q

What increases resistance to flow? (4)

A

Friction increase
Viscosity increase
Tube length increase
Radius decrease

71
Q

What does a Reynolds number of <2000 suggest?

A

Flow is likely laminar

72
Q

Which Reynolds number suggests turbulent flow?

A

> 3000

73
Q

Free diffusion

A

Slow movement of a substance from area of high concentration to area of low concentration

74
Q

What concept is xrms = √2Dt referring to?

A

Diffusion- average distance travelled by molecules

75
Q

Ficks law (diffusion)

A

Free diffusion is proportional to the change of concentration with distance

76
Q

What does osmosis cause at the membrane?

A

A pressure difference

77
Q

Osmotic pressure

A

Minimum pressure that needs to be applied to prevent osmosis

PHSI (6 decks)

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