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A level Physics > Unit 1.5 - Solids Under Stress > Flashcards

Unit 1.5 - Solids Under Stress Flashcards

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1
Q

What happens when an object is subject to tensile force (tension)?

A

It stretches

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2
Q

When does an object stretch?

A

When it’s subject to tensile force

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3
Q

Tensile force

A

Tension

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4
Q

What type of force is tension?

A

A tensile force

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5
Q

What does Hooke’s Law state?

A

For most objects, the degree it stretches is directly proportional to the tension (provided the force is not too large)

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6
Q

“For most objects, the degree it stretches is directly proportional to the tension” - which law is this?

A

Hooke’s law

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7
Q

What type of behaviour does an object exhibit under Hooke’s law?

A

Elastic behaviour, meaning that if it’s subject to too great a stress, the object fractures

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8
Q

Under which law does an object exhibit elastic behaviour?

A

Hooke’s law

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9
Q

What type of graph stops being linear before an object fractures?

A

Tension-extension graph

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10
Q

What does a tension-extension graph show before an object that follow’s Hooke’s law fractures?

A

It stops being linear

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11
Q

What type of materials enter a plastic region and what does this occur to happen?

A

Ductile materials, meaning they’re permanently deformed by the tension

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12
Q

In which region are objects permanently deformed under tension?

A

The plastic region

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13
Q

What do ductile materials do to be permanently deformed by tension?

A

Enter the plastic region

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14
Q

What would show a more stiff object on a force-extension graph?

A

A steeper line

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15
Q

What would a steeper line on a force-extension graph show?

A

A more stiff object

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16
Q

How is the force-extension graph set out? Why?

A

Extension on the x-axis, force on the y-axis
Tensile testing machines are usually designed to apply a specific extension and measure the tension produced

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17
Q

What are tensile testing machines usually designed to do?

A

Apply a specific extension and measure the tension produced

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18
Q

What type of machines measure the tension of an object?

A

Tensile testing machines

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19
Q

What does the gradient on a force-extension graph show?

A

The stiffness of the object (spring constant for the spring)

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20
Q

On what type of graph is the gradient the stiffness of the object (spring constant for the spring) ?

A

Force-extension

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21
Q

What shows the stiffness of an object (spring constant for a spring) on a force extension graph?

A

The gradient

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22
Q

Spring constant

A

The force per unit extension

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23
Q

The force per unit extension

A

The spring constant

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24
Q

Hooke’s law equation

A

F = kx

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25
Q

What is the spring constant in Hooke’s Law’s equation?

A

K
(F = kx)

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26
Q

Spring constant unit

A

Nm-1

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27
Q

How do we work out the gradient?

A

Change in y
——————
Change in x

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28
Q

What does the area underneath show on a force-extension graph?

A

The work done stretching the object
(For elastic materials - the elastic potential energy stored)

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29
Q

What shows the work done stretching the object and For elastic materials - the elastic potential energy stored) on a force-extension graph?

A

The area underneath the graph

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30
Q

The area underneath which type of graph show the work done in stretching an object (or the elastic potential energy stored in elastic materials)?

A

Force-extension

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31
Q

For what type of objects does the area underneath a force-extension graph show elastic potential energy stored?

A

Elastic materials

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32
Q

Elastic potential energy

A

The energy possessed by an object when it has been deformed due to forces acting on it

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33
Q

The energy possessed by an object when it has been deformed due to forces acting on it

A

Elastic potential energy

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34
Q

Elastic strain

A

Strain that disappears when the stress is removed - the specimen returns to its original size and shape

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35
Q

Strain that disappears when the stress is removed - the specimen returns to its original size and shape

A

Elastic strain

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36
Q

Plastic strain

A

When a material is permanently deformed
Atoms have been re-arranged
Mainly in ductile materials

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37
Q

“When a material is permanently deformed due to atoms being re-arranged” - what type of strain is this?

A

Plastic strain

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38
Q

What type of materials experience plastic strain?

A

Ductile materials

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39
Q

How does a material become deformed during plastic strain?

A

Atoms become re-arranged

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40
Q

Brittle

A

A material that does not deform plastically (snaps before reaching this)

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41
Q

What type of material does not not deform plastically and what does it do instead?

A

Brittle materials
Snap before reaching this

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42
Q

Fracture

A

When the material breaks
Fracture can be ductile or brittle

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43
Q

When a material breaks

A

Fracture

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44
Q

What are the two forms of fracture?

A

Ductile or brittle fractures

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45
Q

Ductile

A

The ability of a material to deform plastically
A ductile material can be drawn into wires

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46
Q

What type of material can be drawn into wires?

A

Ductile materials

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47
Q

The ability of a material to deform plastically

A

Ductility

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48
Q

Deform

A

Change in shape due to a stress

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49
Q

Change in shape due to a stress

A

Deform

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50
Q

Stiffness

A

A measure of the materials resistance to deformation
Is related to Young’s Modulus
(Higher = stiffer)

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51
Q

A measure of a material’s resistance to deformation

A

Stiffness

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52
Q

What does a higher Young’s modulus mean?

A

A stiffer material

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53
Q

What figure would mean a stiffer material if it was higher?

A

Young’s modulus

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54
Q

Hooke’s law

A

The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great

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55
Q

The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great

A

Hooke’s law

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56
Q

What prevents the atoms of an object being pulled apart or pushed together?

A

The forces between the atoms

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57
Q

How much does an object extend by when a force is applied?

A

Δl

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58
Q

If a bar has its cross-sectional area increased to 2A, how much is the total F that needs to be applied for the same Δl?

A

2F

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59
Q

Which ratio must be kept the same if two bars of the same composition and length will be stretched by the same amount?

A

F/A ratio

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60
Q

What is “two bars of the same composition with the same length will be stretched by the same amount if the ratio F/A is the same” the definition for?

A

Tensile stress

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61
Q

What’s the symbol for tensile stress?

A

σ

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62
Q

What’s σ the symbol for?

A

Tensile stress

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63
Q

Tensile stress definition

A

The force per unit area applied when equal forces act on a body

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64
Q

The force per unit area applied

A

Tensile stress

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65
Q

Stress equation

A

Stress (σ) = force
———
Cross sectional area (m^2)

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66
Q

What’s F/A the equation for?

A

Stress

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67
Q

Unit of stress

A

Pa

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68
Q

What’s the total extension if two bars are welded end to end and why?

A

2Δl, as tension has the same value (F) in each half, so each half extends by Δl

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69
Q

Which ratio is the same for two bars of the same composition, same cross-sectional area and same tension?

A

Δl
—
l

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70
Q

Under which conditions is the Δl/l ratio the same?

A

With two bars of the same composition, the same cross-sectional area and the same tension

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71
Q

What is the Δl/l quantity known as?

A

Tensile strain

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72
Q

Tensile strain symbol

A

ε

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73
Q

ε meaning

A

Tensile strain

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74
Q

Strain equation

A

Strain (ε) = extension (Δl)
———————
Original length (l)

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75
Q

What’s extension (Δl). the equation for?
———————
Original length (l)

A

Strain

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76
Q

Units of strain

A

No units (remember to make this clear)

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77
Q

What’s proportional in the elastic region?

A

Force is proportional to extension
(Stress is proportional to strain)

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78
Q

In which region is force proportional to extension (stress proportional to strain)?

A

The elastic region

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79
Q

Young’s modulus in simple terms

A

How stiff a material is

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80
Q

Young’s modulus symbol

A

E

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81
Q

E symbol meaning

A

Young’s modulus

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82
Q

What does a higher Young’s modulus value mean for a material?

A

More stiff = less elastic deformation

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83
Q

What would show that a material is more stiff and what would this lead to?

A

A higher Young’s modulus value
Less elastic deformation

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84
Q

What type of material experiences less elastic deformation?

A

A stiff material

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85
Q

Young’s modulus equation (in data book)?

A

E = σ
—
ε

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86
Q

What’s E = σ the equation for calculating?
—
ε

A

Young’s modulus

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87
Q

How do we actually work out Young’s modulus?

A

E = Fl
—
AΔl

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88
Q

Units of Young’s modulus

A

Nm-2 or Pa

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89
Q

Which type of material has the highest Young’s modulus value?

A

Ceramics

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90
Q

Which material has a medium Young’s modulus?

A

Metals

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91
Q

Which type of material has the lowest Young’s modulus?

A

Polymers

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92
Q

Which two types of materials have the highest Young’s modulus values and why?

A

Ceramics and metals
Interatomic bonds (strong)

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93
Q

Which type of material has the lowest Young’s modulus value and why?

A

Polymers
Intermolecular bonds = weak

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94
Q

Which are the strongest - interatomic bonds or intermolecular bonds?

A

Interatomic bonds

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95
Q

How do we calculate elastic potential energy? Why?

A

Tensile force x extension
As work = force applied x distance in that direction

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96
Q

What’s the area underneath a force-extension graph?

A

Energy stored in the material

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97
Q

What shows the energy stored in the material in an extension-force graph?

A

Area underneath

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98
Q

The area underneath which type of graph shows the energy stored in the material?

A

Extension-force

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99
Q

What’s the equation for calculating the energy stored in a material/work done by it?

A

1/2fx OR 1/2kx^2

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100
Q

What are 1/2fx and 1/2kx^2 used for calculating?

A

The energy stored in a material

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101
Q

Which elements go across each axis on an extension-force graph?

A

Extension - x-axis
Force - y-axis

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102
Q

What do we do if the extension and force are along the wrong axes on an extension-force graph?

A

The spring constant is calculated as 1/gradient

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103
Q

When is spring constant calculated as 1/gradient

A

When the extension and force are along the wrong axis on an extension-force graph

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104
Q

What type of samples do we use for stress-strain curves?

A

Samples of uniform cross-sectional area

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105
Q

What do stress-strain curves analyse?

A

Te strength of solids under tension

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106
Q

What does the precise shape of the stress-strain curve vary with?

A

-type of material
-history of the material (e.g - heat or working treatment)

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107
Q

Draw and label a typical stress-strain curve

A

(Check notes)

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108
Q

What comes first on a stress-strain curve - the elastic limit or the limit of proportionality?

A

The limit of proportionality

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109
Q

Where on a stress-strain curve would the gradient be the Young’s modulus of the material?

A

On the limit of proportionality

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110
Q

What does the limit of proportionality show for a material and how on a stress-strain curve?

A

The gradient is the Young’s modulus of the material

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111
Q

How do we find out the Young’s modulus of a material on a stress-strain curve?

A

At the limit of proportionality

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112
Q

The gradient of which part of a stress-strain curve shows the Young’s modulus of the material?

A

The limit of proportionality

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113
Q

In which region on a stress-strain curve is the strain directly proportional to the stress and can deformation be reversed?

A

Elastic region

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114
Q

What is the relationship between stress and strain in the elastic region?

A

Directly proportional

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115
Q

What can occur to a material in the elastic region alone?

A

Deformation can be reversed

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116
Q

What occurs beyond the elastic region?

A

Plastic deformation

117
Q

Beyond which point does plastic deformation occur?

A

Beyond the elastic region

118
Q

What happens if the stress is removed at the elastic limit of a material?

A

The material returns to its normal size

119
Q

Beyond which point is he deformation of a material permanent?

A

Beyond the yield point

120
Q

What does a material show at its yield point?

A

A large increase in strain for little or no increase in stress

121
Q

At which point is a large increase in strain shown for a material for little or no increase in stress?

A

The yield point

122
Q

Which part on a stress-strain curve shows when an object is experiencing necking?

A

Where the curve bends downwards

123
Q

What the curve of the stress-strain bending downwards show?

A

Where the material experiences necking

124
Q

Necking

A

A narrowing of the region where the sample will eventually break

125
Q

A narrowing of the region where the sample will eventually break

A

Necking

126
Q

What does what type of materials does necking occur to?

A

Ductile materials deforming plastically

127
Q

Which type of materials don’t experience necking?

A

Brittle materials that don’t deform plastically

128
Q

What does necking increase on the object?

A

The stress

129
Q

What is necking caused by?

A

An increased number of edge dislocations, causing the wire to lengthen

130
Q

How does necking actually occur?

A

The volume is constant, but the cross-sectional area is decreasing so the stress point increases until the material breaks

131
Q

Which materials are the only ones to experience plastic deformation?

A

Ductile materials

132
Q

What does plastic deformation derive from?

A

Crystalline structure

133
Q

What does the crystalline structure derive?

A

Plastic deformation

134
Q

What happens when a metal crystal forms (to help explain plastic deformation)?

A

Edge dislocations will frequently appear where a plane of atoms will not be complete before the next plane

135
Q

When do edge dislocations frequently appear in a material?

A

When a metal crystal forms

136
Q

How is a dislocation represented on an atomic diagram?

A

A gap

137
Q

What does a gap in an atomic diagram represent?

A

A dislocation in the regular array of atoms

138
Q

What happens in terms of a dislocation of a material when the force is large enough?

A

The bond next to the dislocation is stretched further and will snap, causing the dislocation to move, then bonding to the next atom

139
Q

What happens to the bonds between atoms when a force is applied? Why?

A

The bonds between atoms will stretch as extra stress is caused to the bonds

140
Q

When will the bonds between atoms stretch? Why?

A

When a force is applied, as extra stress is cause to the bonds

141
Q

Give a molecular description of plastic deformation

A

-if the force applied is large enough, the bond next to the dislocation is stretched further, and will snap, causing the dislocation to move
-the free atom bonds with the next
-the process continues until the last bond is formed and the dislocation has moved to the edge of the crystal or grain as each plane has slides over the nearest one

142
Q

What can we see following plastic deformation?

A

When the tensile stress is removed, the changed shape remains, giving us a longer material

143
Q

What do metals contain which results in a large increase in strain with little stress?

A

Edge dislocations

144
Q

Which type of materials contain many edge dislocations an what does this result in?

A

Metals, resulting in a large increase in strain with little stress

145
Q

What does a material containing many edge dislocations cause?

A

A large increase in strain with little stress

146
Q

What would make an object permanently longer?

A

Plastic deformation

147
Q

How are metals strengthened?

A

Impurities are introduced

148
Q

What does introducing impurities to a material do?

A

Strengthens it

149
Q

How do impurities strengthen a material?

A

Create a barrier for dislocation movement

150
Q

What create a barrier for dislocation movement and what does this do to a material?

A

Impurities
Makes them stronger

151
Q

What are the 3 main classifications of solids?

A

Crystalline, amorphous, polymeric

152
Q

What are crystalline, amorphous and polymeric?

A

3 main classifications of solids

153
Q

What do the classifications of solids depen on?

A

The order and structure of he atoms and molecule in the material

154
Q

Crystal

A

A solid in which atoms are arranged in a regular array, with a long-range order

155
Q

A solid in which atoms are arranged in a regular array, with a long-range order

A

Crystal

156
Q

Polycrystalline

A

Consists of many crystals known as grain, arranged randomly

157
Q

What classification of a solid consists of many crystals known as grain, arranged randomly?

A

Polycrystalline

158
Q

What are the many crystals in a polycrystalline structure known as?

A

Grain

159
Q

What type of materials have polycrystalline structures?

A

Metals
Many ionic minerals (e.g - salt)

160
Q

What type of structures do metals and ionic minerals such as salt have?

A

Polycrystalline

161
Q

What’s the name for the space between grains in a polycrystalline structure?

A

Grain boundary

162
Q

Grain boundary

A

Space between grains in a polycrystalline structure

163
Q

Amorphous solid

A

Atoms are arranged randomly, with no regular order

164
Q

In what type of solid are atoms arranged randomly with no regular order?

A

Amorphous solid

165
Q

What type of solids do we use to describe amorphous ones?

A

Brick and glass

166
Q

What type of solids a are back and glass?

A

Amorphous solids

167
Q

Why are brick and glass not perfect examples of amorphous solids?

A

Although there’s no long-range order in the way atoms are arranged, there may be ordered clusters of atoms

168
Q

Polymeric solid

A

Long, chain-like molecules

169
Q

Long, chain-like molecules solid classification

A

Polymeric solid

170
Q

Examples of which type of solid classification are rare?

A

Amorphous solids

171
Q

Examples of polymeric solids

A

Rubber, wood, synthetic polymers (e.g - nylon and polythene)

172
Q

What are rubber, wood and synthetic polymers such as nylon and polythene examples of?

A

Polymeric solids

173
Q

Example of a brittle material

A

Glass

174
Q

What type of material is glass?

A

Brittle

175
Q

What are proportional for brittle materials?

A

Stress and strain

176
Q

Do brittle material’s obey Hooke’s law?

A

Yes

177
Q

Which region on the stress-strain graph to brittle materials remain in?

A

Elastic region

178
Q

Compare the breaking stress of ductile and brittle materials

A

Much smaller for brittle materials

179
Q

What type of material has the smallest breaking stress?

A

Brittle materials

180
Q

What type of material tend to have higher Young’s modulus? What does this mean for it?

A

Brittle material - they’re stiffer

181
Q

Compare the Young’s modulus of brittle and ductile materials

A

Higher for brittle materials

182
Q

Can brittle materials be deformed plastically? Why?

A

No, since they do not have a crystalline structure (amorphous)

183
Q

What structure do brittle materials have?

A

Amorphous

184
Q

What type of materials are amorphous?

A

Brittle ones

185
Q

What type of material cannot be deformed plastically? Why?

A

Brittle materials, as they don’t have a crystalline structure

186
Q

What happens to a brittle material when the elastic limit is reached?

A

They break

187
Q

What type of material breaks when the elastic limit is reached?

A

Brittle

188
Q

At which point does a brittle material break?

A

At the elastic limit

189
Q

Describe how brittle materials break and give a reason why

A

“Cleanly” due to small imperfections (scratches) on the surface that cause stresses to be concentrated on particular bonds

190
Q

What type of materials break “cleanly” and why?

A

Brittle materials due to small scratches/imperfections on the surface that cause stresses to be concentrated in on area

191
Q

What do scratches on the surface of a brittle material do?

A

Cause a material to break “cleanly” as stresses are concentrated on particular bonds

192
Q

Where do the bonds break in a brittle material why?

A

By the tip of the crack due to the stress being high here

193
Q

How does a crack elongate in a brittle material?

A

As the bonds break at the tip of the crack (stress here is high), the stress is transferred to place more tension in the next bond along (the crack elongates, resulting in even higher stress at the tip) and the material breaks in the same direction (but not along a plane)

194
Q

What happens when a crack elongates in a brittle material?

A

There’s an even higher stress at the tip and the material breaks in the same direction

195
Q

When is there even higher stress at the tip of a crack in brittle materials?

A

When it elongates

196
Q

What increases at the tip of a crack as it elongates in a brittle material?

A

Stress

197
Q

How does a material break during a brittle fracture?

A

In the same direction, but not along a plane

198
Q

What prevents crack propagation in a brittle material?

A

Increasing the breaking stress

199
Q

What prevents crack propagation in a brittle material?

A

Increasing its breaking stress

200
Q

In which way does a compression force move on a concrete block?

A

Inwards

201
Q

In which direction does the tension force move on a concrete block?

A

Ouwards

202
Q

How does tension affect normal concrete?

A

Cracks
Fails at a lower force

203
Q

Which force is responsible for making concrete crack and in which direction does this act?

A

Tension, outwards

204
Q

What happens when pouring concrete over steel rods under tension?

A

No cracks (at lower forces)
Fails at approx. 2x the load

205
Q

When does concrete fail when poured over steel rods under tension in comparison to normal concrete?

A

At approx. 2x the load

206
Q

What enables concrete to be able to last approx. 2x the original load?

A

Pouring it over steel rods under tension

207
Q

Draw the forces acting on normal concrete v.s concrete poured over a steel rod under tension

A

(Check notes)

208
Q

Name 2 ways of increasing the breaking stress of a brittle material

A
  1. Reduce the number of surface cracks
  2. Form the material under compression
209
Q

Example of reducing the number of surface cracks on a material to increase its breaking stress

A

Thinner glass fibres have less cracks per unit area as thy have cooled more quickly - do not propagate as readily

210
Q

What type of glass do not propagate as readily and why?

A

Thinner glass fibres, have cooled more quickly and therefore have fewer cracks per unit area

211
Q

How do thin glass fibres have few cracks per unit area? What does this lead to?

A

Have been cooled more quickly - do not propagate as readily

212
Q

Examples of materials formed under compression

A

Toughened glass and prestressed concrete

213
Q

What does forming a material under compression do?

A

Stops cracks opening up and propagating

214
Q

How is concrete pre-stressed?

A

Poured around steel rods under tension and when the tension is released, the concrete will be under compression

215
Q

What does compression do to a crack?

A

Stress acts to close the crack

216
Q

What does a crack do under …
Compression
Tension

A

Stress acts to close crack
Concentrated stress - the crack propagates

217
Q

Why does the crack propagate on a brittle material under tension?

A

The stress is concentrated

218
Q

Rubber

A

A polymer, formed of long chains of bonded carbon atoms

219
Q

Name a polymer formed of long chains of bonded carbon atoms

A

Rubber

220
Q

Which atoms bonded is rubber made of?

A

Bonded carbon atoms

221
Q

What structure does rubber have?

A

Polymeric

222
Q

Which bond can rotate in rubber and what does this allow it to do?

A

C-C bond, so the polymer molecule can assume a huge number of random shapes

223
Q

What can the C-C bond in rubber do and what does this lead to?

A

Rotate so the polymer molecule can assume a huge number of random shapes

224
Q

How can a rubber molecule assume a large number of shapes?

A

The C-C bond can rotate

225
Q

What IS polymer?

A

Polymerised isoprene

226
Q

Polymerised - what? Is rubber?

A

Isoprene

227
Q

Draw isoprene’s molecular structure

A

(Check notes)

228
Q

What happens during the polymerisation of isoprene?

A

The two double bonds are opened up, enabling repeating units to link together to produce poly-isoprene, where the 2 central carbons are double bonded

229
Q

Draw poly-isoprenes molecular structure

A

(Check notes)

230
Q

What are double bonded in poly-isoprene?

A

The 2 central carbons

231
Q

What’s significant about the 2 central carbons in poly-isoprene?

A

Double bonded

232
Q

What is poly-isoprene?

A

Rubber

233
Q

What’s the difference between C=C and C-C bonds?

A

C=C —> not free to rotate
C-C —> free to rotate

234
Q

Which type of bond is free to rotate C-C or C=C bonds?

A

C-C bonds

235
Q

Describe the structure of a rubber molecule

A

“Tangled up”

236
Q

Why is the structure of rubber all tangled up?

A

When the molecule is close to other parts of the chain, weak cross linkages are formed

237
Q

What forms cross linkages in rubber?

A

The molecule with other parts of the chain

238
Q

What happens when a stress is initially applied to rubber?

A

The bonds are being stretched and are rotated so that the molecules become straighter

239
Q

Describe the force needed to extend rubber compared to crystalline and amorphous solids

A

Much lower

240
Q

Crystalline material example

A

Metal

241
Q

Amorphous solid example

A

Glass

242
Q

When does rubber become slightly more difficult to stretch?

A

When the molecules are under such stress that they’re more or less straight

243
Q

Draw rubber’s stress-strain curve

A

(Check notes)

244
Q

Describe the first section of the loading curve of rubber

A

Steeper due to weak cross molecular bonds being overcome

245
Q

What makes rubber hard to stretch initially?

A

Weak cross molecular bonds being overcome

246
Q

Describe the second part of the loading section on rubber’s stress-strain curve

A

Gradient decreases since the stress is simply rotating the single C-C bonds as the molecules straighten

247
Q

When does it take little force to extend rubber?

A

When rotating C-C bonds as the molecules straighten

248
Q

Describe the last part of the loading section of rubber’s stress-strain curve

A

Molecules are now straight so more stress is required per unit strain to extend the stronger covalent bonds in the straight chain

249
Q

What is required to extend rubber after the molecules have been straightened and why?

A

More stress per unit strain due to the stronger covalent bonds

250
Q

Does rubber obey Hooke’s law?

A

Only when the force/stress is small

251
Q

What does rubber obey when the stress is small?

A

Hooke’s law

252
Q

Describe the first part of the unloading of rubber on its stress-strain curve

A

Less energy is released than was taken in during loading (heat lost to surroundings)

253
Q

Why is less energy released when unloading rubber than loading it?

A

Heat is lost to surroundings

254
Q

Describe the second part of the unloading part of rubber’s stress-strain curve

A

Similar curve for loading, just lower (less energy)

255
Q

Why is the curve lower for unloading rubber compared to loading it?

A

Energy loss

256
Q

Describe the last part of the stress-strain graph of rubber when its unloaded

A

Curve returns to the origin as the cross-linking weak bonds reform randomly within the polymer chains

257
Q

What happens at the end of stretching rubber?

A

Cross-linking weak bonds reform

258
Q

What is the area under the curve equal to on a stress-strain curve?

A

Work done

259
Q

Is more work done loading or unloading rubber? What evidence backs this up?

A

Loading - work is the area under the graph and this line is higher

260
Q

Elastic hysteresis

A

The extra energy used to stretch a material that’s transferred to vibrational energy

261
Q

The extra energy used to stretch a material that’s transferred to vibrational energy

A

Elastic hysteresis

262
Q

How do we work out hysteresis?

A

The loop inside the curve is the difference between loading and offloading the rubber and is the energy converted into heat during the whole loading/offloading cycle

263
Q

What represents hysteresis on the stress-strain graph?

A

The loop inside the curve

264
Q

What does the loop inside the curve represent on a stress-strain curve?

A

Hysteresis

265
Q

What are the intermolecular bonds that are initially broken upon stretching rubber known as?

A

Van der Waal forces

266
Q

Why is the area under the loading curve greater than the area under the unloading curve on a hysteresis graph?

A

When energy is put into the band when extending it, it also heats up the rubber.
This energy isn’t available as we de-stress the rubber = lower curve

267
Q

When does a rubber band heat up?

A

Only when being stretched

268
Q

Does a higher Young’s modulus mean a stiffer material?

A

So long as the materials are the same size, yes

269
Q

What rule has to apply for a material to be stiffer with a higher Young’s modulus value?

A

The materials have to be the same size

270
Q

What is concrete weak in?

A

Tension

271
Q

What is a steel rod strong in?

A

Tension

272
Q

Name something that’s weak in tension

A

Concrete

273
Q

Name something that’s strong in tension

A

Steel rod

274
Q

Permanent set

A

Where a material is stretched/compressed and doesn’t return to its original length

275
Q

Where a material is stretched/compressed and doesn’t return to its original length

A

Permanent set

276
Q

How is accuracy preserved when drawing a gradient?

A

Drawing a larger triangle

277
Q

Example of a crystalline structure

A

Diamond

278
Q

Diamond structure

A

Crystalline

279
Q

Glass structure

A

Amorphous

280
Q

Material with an amorphous structure

A

Glass

281
Q

What does an increased temperature do to the value of Young’s modulus and why?

A

Increases
Molecules become entangled as vibrations increase, making the material stiffer

282
Q

What causes the value of Young’s modulus to increase?

A

Increase in temperature

283
Q

Explain and show where on a stress-strain curve a sample exhibits necking

A

The largest strain on a stress-strain curve that typically bends downwards
(The end of the stress-strain curve)

284
Q

Why is it useful that the concrete is under compression when pre-stressed?

A

Inhibits crack propagation and they’re forced to close

285
Q

Describe the process by which a brittle material fractures

A

Small imperfections (scratches) on the surface
Causes stresses to be concentrated on particular bonds when under tension

286
Q

Does adding carbon atoms make a material more or less ductile? Why?

A

Less ductile
Create barriers for dislocation movement

287
Q

Does the value for Young’s modulus depend on the size of the material?

A

No

288
Q

Relationship between spring constant and extension

A

Inversely proportional

A level Physics (29 decks)

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