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Physics > Materials (UNFINISHED) > Flashcards

Materials (UNFINISHED) Flashcards

1
Q

Density =

A

Mass / volume

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2
Q

Density

A

Mass per unit volume

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3
Q

Volume of a sphere

A

4/3 pi x r^3

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4
Q

Volume of a cylinder

A

pi x r^2 x l

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5
Q

Hooke’s Law

A

The extension of the material is directly proportional to the applied force(load) up to the limit of proportionality

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6
Q

Hooke’s Law equation

A

Force = Spring constant x Extension

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7
Q

Spring constant

A

Measures the stiffness of a material. The larger the spring constant, the stiffer the material

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8
Q

What does a material obeying Hooke’s Law look like on a force-extension graph

A

Straight line through the origin

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9
Q

Limit of proportionality

A

The point beyond which Hooke’s law is no longer true when stretching a material. The extension is no longer proportional to the applied force

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10
Q

What does the limit of proportionality look like on a graph

A

Where the line starts to curve (flatten out)

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11
Q

Elastic limit

A

The maximum amount a material can be stretched and still return to its original length (above which the material will no longer be elastic)

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12
Q

Where on the force-extension graph is the elastic limit found

A

After the limit of proportionality

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13
Q

What is the gradient of a force-extension graph, with force on the y-axis and extension on the x-axis

A

The spring constant

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14
Q

Tensile forces

A

Forces which stretch the object

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15
Q

Tensile stress

A

The force exerted per unit cross-sectional area of a material

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16
Q

Tensile stress (sigma) =

A

Force applied / cross-sectional area

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17
Q

Ultimate tensile stress

A

Maximum force per original cross-sectional area a wire is able to support until it breaks

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18
Q

Units for tensile stress

A

Pa

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19
Q

Tensile strain

A

Extension per unit length

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20
Q

Tensile strain =

A

Change in length / Original length

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21
Q

Why does strain have no units

A

Because it is a ratio of lengths

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22
Q

What do stress-strain curves describe

A

The properties of materials, e.g. whether they are brittle, ductile, have elastic and or plastic behaviour

23
Q

Yield stress

A

Force per unit area at which the material extend plastically for no/ a small increase in stress

24
Q

What does the area under the Hooke’s Law (straight line) region of the graph represent

A

The elastic strain energy stored per unit volume (only for Hooke’s Law) / work done (for both Hooke’s law and not)

25
Q

Breaking point

A

The stress at this point is the breaking stress. The maximum stress a material can stand before it fractures

26
Q

Elastic region

A

The region of the graph until the elastic limit. In this region, the material will return to its original shape when the applied force is removed

27
Q

Plastic region

A

The region of the graph after the elastic limit. In this region, the material has deformed permanently and will not return to its original shape when the applied force is removed.

28
Q

Equation for the energy stored under a force-extension graph (obeying Hooke’s Law)

A

1/2 x Force x Change in Length

29
Q

What does the area under a force-extension graph which does not obey Hooke’s law represent

A

Work done

30
Q

What happens to the work done before a material reaches its elastic limit

A

It is ALL stored as elastic strain energy

31
Q

What is the second equation for elastic strain energy

A

E = 1/2 x k x (change in length)^2

32
Q

What happens to stress as the force applied to the material increases

A

Stress increases

33
Q

Breaking stress

A

Maximum stress a material can stand before it fractures(breaks)

34
Q

When is a material considered ductile

A

Materials with a high breaking stress are considered ductile, this means it can extend more before breaking because of plastic deformation

35
Q

Examples of a ductile material

A

Copper

36
Q

What is spring energy transformed to when a vertical spring is extended and contracted

A

Kinetic energy and Gravitation potential energy

37
Q

What is elastic potential energy / spring energy transformed to for a horizontal spring

A

Only KE

38
Q

Elastic deformation

A

When the load is removed, the object will return to its original shape

39
Q

Plastic deformation

A

The material is permanently deformed. When the load is removed, the object won’t return to its original shape or length

40
Q

Where on a stress-strain graph does the plastic region start and end

A

Start - At the elastic limit
End - At the point of fracture

41
Q

Brittle materials

A

Very little to no plastic region e.g. glass and concrete

42
Q

Ductile materials

A

Larger plastic region e.g. rubber and copper

43
Q

How to identify a brittle material on any graph up to their breaking point

A

A straight line through the origins with no or negligible curved region

44
Q

How to identify a DUCTILE material on any graph up to their breaking point

A

Straight line through the origin then curving towards the X-axis

45
Q

What does the area between loading and unloading line represent

A

Work done to permanently deform the wire

46
Q

When a metal wire is loaded and stretched beyond its limit of proportionality what does it undergo

A

Plastic deformation

47
Q

After the wire is plastically deformed and the force is removed, what happens

A

The extension decreases and the unloading line is parallel to the loading line (since k is the same) but it does not go through the origin

48
Q

How is energy conserved when a car goes over a bump

A

The energy is absorbed by shock absorbers.
KE is converted to thermal energy which is then dissipated

49
Q

What is the Young Modulus

A

The measure of the ability of a material to withstand changes in length with an added load

50
Q

Why is the Young Modulus useful

A

It gives info about the stiffness of a material
Useful for engineer to make sure the materials used can withstand sufficient forces

51
Q

Definition of Young Modulus

A

Ratio of tensile stress and tensile strain

52
Q

Young modulus =

A

Tensile stress / Tensile strain = Force x original length / cross sectional area x extension

53
Q

Gradient of a linear stress-strain graph

A

young’s modulus

54
Q

Area under linear stress-strain graph

A

Energy stored per unit volume

Physics (10 decks)

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