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A Level Physics > Module 3: Chapter 6 - Materials > Flashcards

Module 3: Chapter 6 - Materials Flashcards

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1
Q

What is a dense material?

A

A material is dense if it has a large mass per unit volume. Solid materials vary in density as elements have different atomic masses but relatively the same size

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2
Q

What is a tough material?

A

A tough material is a material that does not break by snapping cleanly. A tough material is resistant to the propagation of cracks. It is the opposite of brittleness. A tough material will dissipate a large amount of energy per unit area of new fracture surface. It can withstand a lot of kinetic force. It is the area under a stress-strain curve

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3
Q

What is a brittle material?

A

A material is brittle if it breaks by snapping cleanly. The brittleness of a material is caused by fine surface cracks which propagate easily throughout the material

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4
Q

What is a stiff material

A

A material is stiff if it is difficult to stretch or bend the material. The stiffness is indicated by the young modulus

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5
Q

What is a hard material?

A

A material is hard if it is difficult to scratch or dent the surface of the material.

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6
Q

What is a malleable material?

A

A malleable material is a material that is easy to hammer or press a sheet of into a required shape

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7
Q

What is a ductile material?

A

A material is ductile if it is easy to draw into a wire. Metals are ductile as the non-directional metallic bonds allow ions to slide past one another

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8
Q

What is an elastic material?

A

An elastic material is a material that regains its shape after stretching.
- When a metal or ceramic stretches elastically, the bonds between neighbouring atoms extend very slightly.
- In a polymer the atoms rotate about their bonds

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9
Q

What is a plastic material?

A

A material is plastic if it undergoes large permanent streching or distortion before it breaks

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10
Q

What is a strong material?

A

A material which can withstand a lot of static force, it has a high ultimate tensile strength

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11
Q

What is a weak material?

A

A material that cannot withstand much static force, it has a low ultimate tensile strength

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12
Q

How can hardness be measured?

A

The hardness of a material can be measured by dropping a mass and measuring the depth of the indentation. The smaller the depth of the indentation, the harder the material

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13
Q

How do you measure the strength of a material?

A

To test the strength of a material you must find the UTS of the material. A UTS test involves increasing the tension through a material, constantly measuring the extension of the material and plotting a stress-strain graph. The UTS is at the peak of this curve

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14
Q

How do you measure the toughness of a material?

A

A charpy impact test determines the amount of energy absorbed by a material during a fracture. It involved a material with a v-shaped notch in it being struck by a pendulum. A reading then displays the amount of energy absorbed by the material. The more energy absorbed, the tougher the material as it is more resistant to the propogation of a crack through the material. The less energy absorbed, the more brittle the material as it is less resistant to the propogation of a crack through the material

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15
Q

What determines how much a material will stretch when a force acts on them?

A
  • The length
  • The cross-sectional area
  • The young modulus
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16
Q

What is the equation for stress?

A

Stress = force / area
σ = F/A

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17
Q

What is the equation for strain?

A

Strain = extension / original length
ε = e/L

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18
Q

What is stress?

A

The pressure experienced by a material

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19
Q

What is strain?

A

The ratio of the extension of a material compared to its original length

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20
Q

What are the units of stress?

A

Nm⁻² / Pa

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21
Q

What are the units of strain?

A

It has no units as it is a ratio

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22
Q

What is the equation for young modulus of a material?

A

Young modulus = stress / strain
E = σ/ε

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23
Q

What is young modulus?

A

The ratio of stress over strain when they are in direct proportion. It tells you how stiff a spring is

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24
Q

What are the units for you modulus?

A

Nm⁻² / Pa

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25
Q

A metal wire of original length 1.6m, cross sectional area 0.8mm² extends by 4mm when streched by a tensile force of 200N. Calculate the young modulus of the wire.

A

E = 1x10¹¹ Pa

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26
Q

How can young modulus be found from a stress-strain graph?

A

The gradient of the linear section

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27
Q

What does each point on this stress-strain graph represent?

A

P = limit of proportionality
E = elastic limit
Y = yield point
UTS = ultimate tensile strength
B = Breaking point

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28
Q

What is the limit of proportionality?

A

The value of stress on a stress strain graph when the stress is no longer directly proportional to strain

29
Q

What is the elastic limit?

A

The value of stress on a stress-strain graph beyond which elastic deformation becomes plastic deformation, and the material or object will no longer return to its orignial shape and size when the stress is removed

30
Q

What is the yield point?

A

A point on a stress-strain graph beyond which the deformation is no longer entirely elastic

31
Q

What is the difference between elastic limit and yield point?

A

nothing

32
Q

What does the general stress-strain graph of a metal look like? (ductile and tough material)

A
33
Q

What is the area under a stress-strain curve?

A

The energy absorbed by the material before fracture (the toughness)

34
Q

What is the typical stress strain graph for a brittle material?

A
35
Q

Describe each material by its stress-strain curve

A

Red = Brittle
Black = Ductile
Blue = Plastic

36
Q

What is breaking stress?

A

The stress value at the point of fracture

37
Q

What is ultimate tensile strength?

A

The maximum stress that a material can withstand before it breaks

38
Q

What is elastic deformation?

A

Deformation that is reversed once the force deforming it is removed

39
Q

What is a compressive force?

A

A force that acts through a material, shortening it

40
Q

What is a tensile force?

A

A force which acts through a material and produces extension

41
Q

What is plastic behaviour?

A

When the material deforms irreversibly and does not return to its original shape and size, even when the load is removed

42
Q

What is hookes law?

A

The extension of a spring is directly proportional to force applied until the limit of proportionality is exceeded

43
Q

What is the equation for hookes law?

A

F = kx

44
Q

What is k in F = kx?

A

The force/spring constant. It has the units Nm⁻¹. It is the force per unit extension of a spring

45
Q

How do you find the force constant from a force-extension graph?

A

It is the gradient of the linear section

46
Q

What is the area under the graph for a force-extension graph of a spring?

A

The elastic potential energy stored in the spring

47
Q

What is the equation for elastic potential energy?

A

Ee = 0.5ke²
or
Ee = 0.5Fe

48
Q

What is the loading curve?

A

The curve on a force extension diagram as force is being applied to a material

49
Q

What is the unlaoding curve?

A

The curve on a force extension diagram as force is being removed from a material

50
Q

How can you determine the work done to stretch a rubber on a force extension diagram?

A

The area under the loading curve

51
Q

The loading and unloading curves for a rubber are different, what does this mean in terms of work done?

A

When the rubber is unloaded, only the energy equal to the area under the unloading curve is returned. Therefore the area between the loading and unloading curve is the energy transferred to internal energy and lost to heating the rubber

52
Q

Explain how connecting springs in series affects the effective spring constant:

A

For springs in series, each spring experiences the same load. Therefore each spring will extend the same amount as an individual spring would. Therefore the combination is “more stretchy” and the effective spring constant for the combination would be half that for 2 identical spring in series, a third for 3 identical springs in series etc etc

53
Q

What is the equation for effective spring constant of springs in series?

A
54
Q

Explain how connecting springs in parallel affects the effective spring constant:

A

For springs in parallel, the load is shared between each spring and therefore each spring is not stretched as much as they would individually. The combination is therefor “less stretchy” and the effective spring constant for the combination will be twice that of a single spring for 2 identical springs in parallel, 3 times for 3 identical springs etc etc

55
Q

What is the equation for effective spring constant for springs in parallel?

A

Keff = K1 + K2 + K3…

56
Q

What does the stress-strain curve of a polymeric material look like?

A

It is immeditelly deformed plastically

57
Q

What is tensile deformation?

A

deformation from tension

58
Q

What is compressive deformation?

A

Deformation from compression

59
Q

What is the typical loading and unloading curve for a metal wire?

A
60
Q

What is the typical loading and unloading curve for a rubber band?

A
61
Q

What is the typical loading and unloading curve for polythene?

A
62
Q

What is a hysteresis loop?

A

A loop-shaped plot obtained when, for example, loading and unloading a material produce differenet deformations

63
Q

Explain the loading and unloading curve for a metal wire:

A

The loading curve follows hookes law until it reaches the elastic limit. The unloading curve will be identical to the loading curve if it elastic limit is not reached, however if it is reached the unlaoding curve will then be parallel to the loading curve but not identical. There is permanent deformation

64
Q

Explain the loading and unloading curve for rubber:

A

Rubber does not obey hookes law, therefore the loading and unloading curves are not linear but the rubber only undergoes elastic deformation. The only way to achieve plastic deformation is to break the material. More work is done loading the rubber than is dun unloading the rubber, therefore the area within the hysteresis loop is the thermal energy released.

65
Q

Explain the loading and unloading curves for polythene:

A

Polythene does not obey hookes law, it immediately suffers plastic deformation. As it is plastically deformed the unloading curve does not go back to the origin, there is permanent extension

66
Q

What are polymeric materials?

A

Materials that consist of long molecular chains

67
Q

What are 2 examples of polymeric materials and how do they behave differently?

A
  • Rubber - behaves elastically
  • Polythene - behaves plastically
68
Q

What occurs between the UTS point and the breaking point in a metal?

A

the material begins to get longer and thinner at its weakest point, this process is called necking. The material eventually snaps due to this

A Level Physics (29 decks)

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