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Physics AS Rafa > 3.4 Materials > Flashcards

3.4 Materials Flashcards

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1
Q

Define elasticity

A

The property of a body to resume its original shape or size once the deforming force or stress has been removed

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2
Q

Define plastic deformation

A

Material does not return to original length when force is removed

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3
Q

Why don’t plastic materials return to their shapes?

A

Has exceeded its elastic limit

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4
Q

What is A on a force-extension graph?

A

Limit of proportionality

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5
Q

What is B on a force-extension graph?

A

Elastic limit

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6
Q

What is C on a force-extension graph?

A

Plastic behaviour

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7
Q

What is D on a force-extension graph?

A

Fracture

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8
Q

What is elastic limit?

A

Beyond this point it will not show elastic behaviour but plastic

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9
Q

What is the limit of proportionality?

A

The point at which extension is no longer directly proportional to the force
Material behave elastically still
Stops obeying Hookes law

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10
Q

What is fracture?

A

When the material breaks

Before this happens the material undergoes creep

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11
Q

What type of graph is used to show the difference between plastic and elastic behaviour?

A

Force against extension

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12
Q

What is Hookes law?

A

States that extension of an object is proportional to the force that caused it, provided the elastic limit is not exceeded

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13
Q

What is the equation for Hooke’s law?

A

F=kx

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14
Q

What is the unit of the force constant?

A

Nm-1

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15
Q

When do you stop using the force constant?

A

When deformation becomes plastic

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16
Q

Why do we unconventionally plot force on the y axis and extension on the x axis?

A

Because then the gradient of the line is equal to the force constant

17
Q

What does the work required to stretch a wire depend on?

A

Stretching force and extension

18
Q

How do you find work done from a graph?

A

Area underneath

19
Q

Define stress

A

Force per unit cross sectional area.

Nm-2 or Pa

20
Q

Define strain

A

Extension per unit length

No units and is dimensionless

21
Q

What is young modulus?

A

Stress/strain

Or Fl/eA

22
Q

What type of young modulus do stuff materials have?

A

Large

23
Q

What are the two ways to calculate you gs modulus?

A

Gradient of stress/strain graph

Calculate value directly from equation

24
Q

What is ductile?

A

Can be drawn into wires and will show plastic deformation under tensile stress before breaking

25
Q

What is malleable?

A

Can be hammered or beaten into flat sheets and will show extensive plastic deformation when subjected to compressive forces

26
Q

What is brittle?

A

Break with little or no plastic deformation

27
Q

What is a hard material?

A

One that will resist plastic deformation by surface indentation

28
Q

What is stiffness

A

The ability to resist tensile force

29
Q

What is a polymeric material?

A

Made of long chains of polymers and can withstand large strains

30
Q

What is the ultimate tensile strength?

A

The maximum stress it can withstand while being pulled or stretched, before it breaks

31
Q

Precision of micrometer

A

Micrometer to the nearest 0.01mm

32
Q

What’s important when plotting the graph?

A

Through origin

Lobf

33
Q

How to reduce error in Young’s modulus experiment?

A

0 error on micrometer or ruler

Remove by adding or subtracting error

34
Q

Typical Young’s modulus value of a metal?

A

50-100 *10^9 Pa

35
Q

What is the unit of Young’s modulus?

A

Pa

36
Q

What does a stress strain graph for brittle materials look like?

A

Doesn’t curve

37
Q

What does the area under a polymeric material curve?

A

Amount of energy converted to heat per unit volume

38
Q

Why are the losing and unloading curves for rubber different?

A

Energy released when the rubber is unloaded is less than work done to stretch it as some is converted to heat

Physics AS Rafa (12 decks)

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