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A-Level Physics [Edexcel] > Materials > Flashcards

Materials Flashcards

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1
Q

What are the fluids?

A

Liquids and gases are both fluids.

Fluids can flow.

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2
Q

What are the units for:

  1. Density
  2. Mass
  3. Volume
  4. Pressure
  5. Force
  6. Area
  7. Weight
A
  1. kgm⁻³
  2. kg
  3. m³
  4. Pa
  5. N
  6. m²
  7. N
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3
Q

What is the formula for the volume of a sphere?

A

V = ⁴/₃πr³

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4
Q

What is the formula for the surface area of a sphere?

A

V = 4πr²

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5
Q

Link Density to mass and volume.

A

Density = mass / volume.

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6
Q

What character is used to show density?

A

ρ (rho)

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7
Q

Show two ways of working out the pressure a fluid exerts.

A

p = mg / A

(∵ ρ=m/V , m=ρV)
(p = ρVg / A)
(V = Area x hight)

p = ρhg

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8
Q

Given that the density of air is 1.24kgm⁻³, estimate the height of the atmosphere.

A

p = ρhg ∴ h = p/ ρg

The density of air is 1.24kgm⁻³ at sea level and virtually 0 at the upper atmosphere, so the average is 0.62kgm⁻³.

Assume that air pressure is 100,000Pa (∵1atm =100kPa)

g = 9.81 on eath which is ≈ 10

100000 / (10 x 0.62)
100000 / 6.2 = 16129.0 …
= 16000km

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9
Q

Derive this relationship from equations on the formula sheet:

W = ρVg

A

W = mg
ρ = m/V → m= ρV
∴ W =ρVg

p = F / A
F = W
∴ p = W / A

W = mg
ρ = m/V → m= ρV
∴ W =ρVg

∴ p = ρVg / A
V and A cancel out to give h (∵ V = lwh = Ah)
∴ p = ρhg

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10
Q

Derive this relationship from equations on the formula sheet:

p = ρhg

A

p = F / A
F = W
∴ p = W / A

W = mg
ρ = m/V → m= ρV
∴ W =ρVg

∴ p = ρVg / A
V and A cancel out to give h (∵ V = lwh = Ah)
∴ p = ρhg

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11
Q

What is upthrust?

A

Weight (a force) of fluid displaced.

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12
Q

What does Archimedes’ principle stare?

A

That when a body is totally or partially immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced.

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13
Q

What is ρᵥᵥₐₜₑᵣ?

A

1000 kgm-3

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14
Q

What are streamlines?

A

Lines to show the path taken by small regions of a fluid.

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15
Q

What streamlines show laminar flow?

A

Streamlines which do not cross over each other.

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16
Q

What streamlines show turbulent flow?

A

Streamlines which cross, leading to the formation of vortices and eddy currents.

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17
Q

What causes turbulent flow?

A

When the speed of laminar flow increases past the critical speed.

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18
Q

What does a fluids critical speed depend on?

A

The fluid and the shape of the area in which it is flowing.

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19
Q

What does Stoke’s Law calculate?

A

A value for the viscous drag of an object moving relative to a fluid.

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20
Q

When can Stoke’s Law be applied?

A

Stoke’s Law applies specifically to:
1. Small spherical objects

  1. Moving at low speeds with laminar flow (or in the absence of turbulent flow)
  2. At constant temperature (viscosity is temperature dependent)
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21
Q

What are each of the values in Stoke’s Law?

A

F = 6πηrv

F = viscous drag acting on a sphere (in a laminar flow of liquid).

η = coefficient of viscosity (the resistance to flow).

r = radius of the sphere.

v = velocity of the sphere relative to the fluid.

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22
Q

Describe the forces on an object falling through a fluid at terminal velocity.

A

At terminal speed, the upwards forces of upthrust and drag and the downward force of the weight are balanced.

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23
Q

What is viscosity?

A

The quantity that describes a fluid’s resistance to flow.

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24
Q

Write an expression for drag in terms of D, U, and W:

1) in a falling object?
2) in a rising object?

A

1) D = U-W

2) D = W-U

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25
Q

When does _____ act on an object in a fluid?

1) Weight
2) Upthrust
3) Drag

A

1) Always
2) Always
3) On moving objects

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26
Q

In what direction does _____ act on an object in a fluid?

1) Weight
2) Upthrust
3) Drag

A

1) Downwards
2) Upward
3) Opposite to the direction of motion

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27
Q

How is _____ calculated when in fluids?

1) Weight
2) Upthrust
3) Drag

A

1) W = mg
2) U = ρVg
3) D = 6πηrv

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28
Q

How would you calculate the terminal velocity of a ball, given the following information?

A lead ball of diameter 7.65 mm dropped through oil reaches terminal velocity. Lead has a density of 11400 kgm-3.

Oil properties
ρ = 915 kgm-3
η = 0.0385 Pas

A

1) Draw a free body force diagram for the ball
2) Calculate the weight of the ball
3) Calculate the upthrust acting on the ball
4) Find the drag acting on the ball
5) Calculate the terminal velocity of the ball
6) State any assumptions that you have made

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29
Q

What is hardness?

A

how difficult it is to scratch the surface.

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30
Q

What is stiffness?

A

how much it deforms under large forces.

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31
Q

What is toughness?

A

how much energy from impacts it can absorb without breaking.

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32
Q

What is brittleness?

A

how much it will shatter or crack when subjected to a shock.

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33
Q

What is strength?

A

how much breaking stress it can withstand.

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34
Q

What is malleability?

A

how easily it can be formed into thin sheets.

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35
Q

What is ductility?

A

how easily it can be drawn into a wire.

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36
Q

What is Hooke’s Law?

A

The extension of a stretched wire is directly proportional to the force acting on the wire.

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37
Q

What is Hooke’s Law quantitively and what do each of the values mean?

A

ΔF = kΔx

ΔF: Forces acting.

k: is the force constant (stiffness of the wire).

Δx: extension.

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38
Q

When can Hooke’s Law be applied?

A
  • To all solids.

- Up to their limit of proportionality.

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39
Q

What happens to the spring constant and extension when springs are added in series?

A

1/k = (1/k₁) + (1/k₂) + …

  • k is smaller
  • Δx is larger
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40
Q

What happens to the spring constant and extension when springs are added in parallel?

A

k = (k₁) + (k₂) + …

  • k is larger
  • Δx is smaller
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41
Q

What is elastic deformation?

A

The material will return to its original shape when the deforming force is removed.

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42
Q

What is plastic deformation?

A

The material will remain deformed when the deforming force is removed.

43
Q

What is the limit of proportionality?

A

The point where Hooke’s Law ceases to be obeyed.

The maximum extension (or strain) that an object (or sample) can exhibit, which is still proportional to the load (or stress) applied.

44
Q

What is Hooke’s Law applied on a graph?

A

The points which show direct proportionality

  • A straight line.
  • Passing through the origin.
45
Q

What is the elastic limit?

A

The point beyond which the wire will not regain its original shape when the deforming force is removed.

Often the same point as the limit of proportionality

46
Q

What is the yield point?

A

Where plastic deformation begins.

A large increase in strain/extension is seen for a small increase in stress/Force.

47
Q

What is the elastic region?

A

The region where the material deforms elastically.

Between origin and elastic limit.

48
Q

What is the plastic region?

A

The region where the material deforms plastically.

Between elastic limit and snapping point.

49
Q

What is the ultimate tensile stress?

A

The maximum stress that is applied to a wire without its snapping.

Beyond the UTS, the force required to snap the wire is less.

50
Q

On a force-extension graph, what does an upwards slope represent?

A

Loading.

51
Q

On a force-extension graph, what does a downwards slope represent?

A

Unloading.

52
Q

On a force-extension graph, what does a linear section of the graph show?

A

Linear (un)loading.

53
Q

On a force-extension graph, what does a curved section of the graph show?

A

Non-linear (un)loading.

54
Q

How is unloading show on a force-extension / stress-strain graph?

A

A dotted/dashed line if the material snaps.

A line below if not.

55
Q

What happens inside the material, during the elastic region?

A
  • The bonds between atoms increase in length, due to the forces on the material.
  • But revert to their usual length when the force is removed, and the atoms return to their equilibrium positions.
56
Q

What happens inside the material, beyond the elastic limit (in the plastic region)?

A
  • The arrangement of atoms has changed and the material has undergone permanent (plastic) deformation.
  • It may contract when the force is removed, but not to its original shape.
57
Q

What happens inside the material, beyond the yield point (still in the plastic region)?

A
  • The atoms move as layers, which slide over each other with no restorative forces.
  • The material will not contract when the force is removed.
58
Q

What is Elastic strain energy?

A

The ability of a material to do work as it returns to its original dimensions.

59
Q

How is Elastic strain energy calculated?

A

work done = average force x distance moved

W = FₐᵥΔx

60
Q

How is Elastic strain energy calculated, in objects that obey hook’s law?

A

Elastic strain energy = ¹/₂ x force x distance moved

Eₑₗ= ½F∆x

61
Q

How is Elastic strain energy calculated from a graph?

A

The area under a graph.

62
Q

How would you determine which material is stiffer from graphs?

A

Stiffer → steeper gradient.

63
Q

How would you determine which material is tougher from graphs?

A

Tougher → greater area under graph.

64
Q

How would you determine which material is more brittle from graphs?

A

More Brittle → Less/no plastic deformation when it breaks.

65
Q

What is tension?

A

A force acting within a material in a direction that would extend the material.

66
Q

What is extension?

A

An increase in the size of ta material sample caused by a tension force.

67
Q

What is compression?

A

A force acting within a material in a direction that would squash the material.

Also, the decrease in size of a material sample under a compressive force.

68
Q

What is hysteresis?

A

Where the extension under a certain load will be different depending on its history of past loads and extensions.

69
Q

Why does stress, strain and Young Modulus better compare objects than Force-extension?

A

Because Force-extension, although individual, depends on the dimensions of the objects.

70
Q

What is stress?

A

A measure of the force acting within a material.

71
Q

What does tensile stress cause?

A

Stretching.

72
Q

What does compressive stress cause?

A

Squashing.

73
Q

What is the formula for stress?

A

Force (N) / cross-sectional area (m²)

σ = F/A

74
Q

How are stress and pressure different?

A

Pressure is external.

Stress is internal.

75
Q

What is the unit for stress?

A

Nm⁻²

76
Q

What is strain?

A

The extension of the material compared to its original length.

77
Q

What cuases strain?

A

Stress

78
Q

What is the formula for strain?

A

strain = extension / original length

ε = Δx / x

79
Q

What is the unit for stress and why?

A

No units.

∵ it is a ratio

You can also give it as a %

80
Q

How is strain different to extension?

A

Starin shows the difference in extension from the original length.

81
Q

Why would we use strain instead of extension?

A

It is comparable.

82
Q

What happens when a material deforms elastically?

link to stress-strain

A

The stress is proportional to the strain.

83
Q

What is Young modulus?

A

A constant of proportionality that shows the stiffness of the material.

84
Q

Why is Young modulus used for comparing different materials?

A

It is a property of the material.

So, different shaped objects made from the same material will have the same Young modus.

Therefore it means you can use it to compare any material despite its dimensions

85
Q

How is Young modulus calculated?

A

Young Modulus = stress / strain

E = σ / ε

86
Q

How else can E = σ / ε be shown?

A

Fx / AΔx

87
Q

What is the unit for Young modulus?

A

Pascals (Pa)

88
Q

What does the gradient of a stress-strain graph show?

A

Young modulus.

89
Q

What does the area under a stress-strain graph show?

A

Toughness.

90
Q

What is breaking stress?

A

The stress in a material when it breaks.

91
Q

Materials with a high breaking stress are ______.

A

Strong.

92
Q

Why isn’t the breaking stress the same as the ultimate tensile strength?

A

The ultimate tensile stress is the maximum amount of stress an object can store before it breaks.

Whereas, the breaking stress can be smaller than this.

93
Q

A steep gradient shows that a material is ______.

A

Stiff.

94
Q

A large area under a graph shows that a material is ______.

A

Tough.

95
Q

What is elastic strain energy?

A

The energy stored when a material is deformed.

96
Q

How is elastic strain energy show in a graph?

A

The area under a force-extension graph.

97
Q

What is a loading line?

A

Work done per unit volume on the band as it stretches

98
Q

What is a unloading line?

A

Work done per unit volume by the band as it contracts

99
Q

What might happen during hysteresis?

A

Some energy has been transferred into internal energy of the band, making it warmer

100
Q

What is energy density?

A

the work done (elastic energy stored) per unit volume of the sample.

101
Q

High energy density shows a material is ______.

A

Tough.

102
Q

How is Young modulus calculated (for a wire that obeys Hooke’s law)?

A

energy density = work done / volume

103
Q

Use equations for stress and strain to prove that this can be found by calculating the area under a stress-strain graph.

A 
energy density = work done / volume
= ΔW / V
= ΔW / As
= Fₐᵥ Δs / As
= ¹/₂FΔs / As
= (¹/₂F / A) x (Δs / s)
= ¹/₂ stress x strain
(which is the area under a stress-strain)

A-Level Physics [Edexcel] (9 decks)

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