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Materials Flashcards

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0
Q

What is the equation for density?

A 
Density = mass/ volume  
P = m/v
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1
Q

Define Density

A

Mass per unit volume

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2
Q

In words what does hooks law state?

A

That the extension of a wire, change in l is proportional to the force applied.

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3
Q

As an equation what does hooks law state?

A

F= k x change in length .

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4
Q

What is an objects stiffness constant ?

A

The force needed to extend it by 1m , it depends on the objects size an shape.

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5
Q

Does hooks law work for compression?

A

Yes

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6
Q

How do you calculate extension

A

New length - old length

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7
Q

On a graph how do you know hooks law is being obeyed?

A

A straight line through the origin.

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8
Q

What is the limit of proportionality?

A

The point beyond which the force is no longer proportional to the extension. The hooks law limit.

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9
Q

What is the elastic limit?

A

The point at which the material will be permanently stretched and not return to the same size.

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10
Q

If a material is stretched past its elastic limit it deforms …..

A

Plasticly

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11
Q

Something that has undergone plastic deformation has …? What does this mean?

A

Gone past the elastic limit and so will not return to its original shape.

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12
Q

Elastic deformation means that …

A

The material will return to its original shape.

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13
Q

Why can materials stretch?

A

The atoms in the material can move small distances relative to their equilibrium positions without changing the structure of the material.

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14
Q

Tensile stress is calculated by

A

Stress = force/ area

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15
Q

What is strains units?

A

It has no units

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16
Q

What is the equation for strain?

A

Tensile strain =

Change in length/ starting length

17
Q

What are the units for stress?

A

Nm^-2 or pascals, Pa

18
Q

What is breaking stress?

A

Stress that I large enough to break apart the material

19
Q

What is the maximum strength a material can withstand called?

A

Ultimate tensile stress (UTS)

20
Q

When an item is stretched, before the elastic limit where is the energy stored?

A

As elastic potential energy

21
Q

When a material is stretched what is the elastic potential energy called?

A

Elastic strain energy

22
Q

What is elastic strain energy?

A

the name for when a material is stretched and energy is stored as the elastic potential energy.

23
Q

What is the area under a stress strain graph?

A

Energy per unit volume

24
Q

How would you find the energy stored (work done) using a force/ extension graph

A

Find the area under the line,

1/2 x force x change in length

25
Q

What is the equation. For energy stored in a stretched/compressed object? What is necessary for this to be true? (Graph)

A

Energy= 1/2 x force x change in length.

The material must be obeying hooks law.

26
Q

How can the energy stored equation also be written?

A

E=1/2k x L^2

* F is replaced by Kl (hooks law)

27
Q

Points on how 1/2xFx delta L is derived. (Energy stored)

A 
Energy stored = work done 
Work done = Fx delta L
Graph is F by change in L 
area under graph is Energy 
Line is proportional and through 0 
Triangle equation for area 0.5BH 
So energy stored is 1/2 x F x delta L
28
Q

What is the point where the material stretches without extra load being added called?

A

The yield point

29
Q

What is the youngs modulus of a material?

A

It is a measure of how stiff a material is, it makes it useful for comparing materials and calculating extension.

30
Q

What is the symbol for youngs modulus?

A

E

31
Q

How is Young’s modulus calculated ( 2 equations)!

A

Stress / strain

FL/ A x change in length

32
Q

Describe an experiment to find the Young’s modulus of a wire.

A

Set up a wire, fixed to a bench at one end and a pulley at the other.

Make sure the wire is thin and long, so it extend more.

Place a marker in the wire. And a mm rule underneath this.

Start with the smallest possible weight to make the make the wire straight with no slack.
This is the un-stretched length.

Increase the weight in steps,recording the change in length from the marker to the start each time.

Use a micrometer to measure the diameter if the wire. Take repeats and take an average to calculate the CS area.

Use this data to calculate Young’s modulus, E

33
Q

What could you use to calculate the cross sectional area?

A

Use a micrometer to find the diameter and then use pieR^2

34
Q

Energy per unit volume =

A

1/2x stress x strain

Area under a stress strain graph.

35
Q

How can you recognise a graph of a brittle material?

A

It follows hooks law with a straight line through the Pravin and then stops, it does not curve of deform plasticly, it snaps.

36
Q

What is 1mm^2 in metres

A

1 x 10 ^-6 M^2

37
Q

Describe the structure of a brittle material.

A

The atoms are often in a crystalline structure. In a brittle material the strong bonds and arrangement means that the atoms can not move much from their equilibrium position.

38
Q

Brittle fracture is when?

A

When stress is applied to a brittle material and tiny cracks at the materials surface get bigger and bigger until the material breaks.

39
Q

When stress is applied to a brittle material and the cracks grow and grow as the atoms can not move much, it is called?

A

A brittle fracture

Physics (12 decks)

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