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physics alevel (theory) > Mod3 : Materials > Flashcards

Mod3 : Materials Flashcards

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1
Q

 What is extension proportional to

A

The load of force

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2
Q

Gives the equation for Hooks law

A

F= kx
Where is the spring constant and X is the extension

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3
Q

What do tensile forces do?

A

They stretch the object

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4
Q

What is the extension or compression proportional to?

A

The force applied

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5
Q

Explain the graph of a an elastic band being stretched

A

First plot a graph of force against extension four the first part of the graph. The elastic band will obey hook law and force will be proportional to extension. However, as it reaches a point graph starts to curve this is the point of limit of proportionality after the limit of proportionality there will be another point where the graph starts to level out and this is the elastic limit. This means the elastic band is permanently stretched and will no longer go back to its original shape.

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6
Q

How do you combine springs in series? What is the equation for it?

A

1/k = 1/k1 + 1/k2 etc
K= spring constant

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7
Q

How do you play spring in parallel what is the equation?

A

K = k1 + k2

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8
Q

Explain what happens within a material when it is under elastic deformation

A

When the material is put under tension , the atoms of the material are pulled apart from one another
Atoms can move slightly relative to their equilibrium positions, without changing their position in the material
And once the load is removed, the atoms can then return to the equilibrium distance. Apart from each other this means the material is not permanently deformed.

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9
Q

Explain what happens within materials when it is plastically deformed

A

Some atoms in the material move position relative to one another, and when the load is removed, the atoms cannot return back to their original position. This means the material is permanently deformed and cannot go back to its original shape.

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10
Q

Describe an experiment to investigate the extension of a spring

A

Set up a clamp stand with a meter ruler placed perpendicular to the floor
Then place a a spring to the clamp
Firstly, measured the unstretched length of the spring, and then add weights one at a time to the bottom of the spring, now record the new length of the spring and calculate the extension by doing extension equals new length minus original length .
Plot a force against extension ,where the line of best fit is straight, spring Constance will be the gradient of the graph and when the limit for proportionality has exceeded the graph will start to curve if you have added that much weight

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11
Q

If forces stretch a material, what are the forces called?

A

Tensile

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12
Q

If forces squash the material, what are the forces called?

A

Compressive

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13
Q

What is tensile stress defined as and what are the units

A

The force applied divided by the cross-sectional area
The units are pascals Pa or Nm^-2

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14
Q

What is tensile strain defined as and what is the equation, and what is the

A

Tinsel strain is defined as the change in length, for example, the extension divided by the original length of the material
The equation is 10 strain equals extension divided by original length.
There are no units for potential strain, and it is only a number

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15
Q

Describe a stress against strain graph and what is happening to the material

A

Put stress on the y axis and strain on the X axis
The effect of stress on a material starts to pull the atoms in the material. Apart from one another event. Eventually, the stress becomes so great that the atoms separate completely and the material breaks. Initially on a stress strain graph, the material will be following hook law. However, the graph starts to curve until the ultimate tensile strength point which is the maximum stress the material can withstand before breaking the graph then comes to a stop and that point is the breaking stress this is where the material has broken.

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16
Q

What is the area under a force extension graph?

A

The elastic potential energy

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17
Q

How do you derive elastic potential energy?

A

The work done on a wire or a material in stretching it is equal to the energy stored therefore work equals force times displacement. However, the force on the material is not constant and it varies from 0 to the force f.Therefore we have to take an average to 0 and the maximum force, this then makes the equation work done equals a half Times force times displacement.
This is the elastic potential energy
However, as hook law is being obeyed by the material, we can say that force equals spring constant times extension which is hook law. You can then stop this into the elastic potential energy which gives us the equation of elastic potential energy. .

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18
Q

Explain a stress strain graph for a typical ductile material, such as a copper wire

A

Initially up until the point, the material will obey owns law and it will be a straight line through the origin. However, as it reaches the point the limit of proportionality, the graph is no longer a straight line but starts to bend at this point the material stopped being hooked along, but it can still return to its original shape if the stress was removed.
As more stress is applied is reached which is the elastic limit. At this point the material starts to behave plastically and cannot go back to its original shape if the stress were removed.
And then reaches the yield point when the material suddenly starts to stretch without any extra load .

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19
Q

What is the yield point?

A

The yield point is the stress, at which a large amount of plastic deformation takes place with a constant or reduced load.

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20
Q

Describe stress , strain graph for brittle materials

A

The graph is a straight line through the origin obeying hook law, however, at a certain point the material snaps and the graph stops abruptly this is because the material does not deform plastically. Therefore, the graph does not curve

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21
Q

What happens when stress is applied to brittle material

A

Tiny cracks at the material surface get bigger and bigger as more stress is applied until the material breaks completely. This is called brittle fracture.

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22
Q

Describe the graph for a stress strain graph for polythene

A

Initially, the material behaves according to hook law, however, at a certain point, the material will behave plastically, therfore The material will stretch into a new shape. Polythene is a ductile material. Initially the graph is a straight line and then there is a small curve going into a loading phase which is a straight horizontal line and then unloading phase which is the same gradient as the initial part of the graph law line.

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23
Q

Describe the graph of a stress, strain graph of a rubber

A

Rubber, behaves, elastically,
However, the loading and unloading curves for rubber are different. The energy released when the rubber is unloaded is less than the work done to stretch the rubber. This is because some of the elastic potential energy stored in the stretched rubber is converted to heat which is why the gradient of the unloading line is shallow than the loading line .
The graph looks like a toothpaste symbol with the loading curve going from an increase to a decreasing to an increased ingredient and the unloading curve going from a decreasing to a slightly increasing to a decreasing curve .

24
Q

On a rubber stress strain graph of a rubber, what represents the energy transferred to the thermal store of the rubber

A

The area between the loading and unloading curves

25
Q

What does a material experience as a load is applied to stretch it

A

It experiences, tensile, stress, and tensile strain

26
Q

What is the relationship between stress and strain of material up to the point of limit of proportionality

A

Up until the limit of proportionality, stress and strain are proportional to each other

27
Q

Explain young modulus and give the equation

A

Up until the limit of proportionality we can say young modulus equals tensile stress divided by tensile strain
Units of young modulus is the same as stress which is pascals and newtons per metres. Squared
Young modulus is a measure of the stiffness of a material
The equation is
E = FL/xA
Where is the unstretched length and X is the extension?

28
Q

Describe an experiment to find the young modulus

A

To find young modulus, you need a very thin and very long wire as the longer the wire, the more the way I can extend for the same force. This reduces the uncertainty in the measurements taken.
First, find the cross-sectional area of the wire by using a micrometre to measure the diameter of the wire in several places, and taking an average, then use the formula for the area of the circle to find the cross-sectional area
Clamp the wire to a bench and attach some weight at the end of the wire, then place the wire over a pulley so that the weights are hanging off the bench
Then measure the distance between the fixed end of the wire, and a mark made on the wire.This is the unstretched length.
The more you increased the weight the more the wire stretches and the marker will move as the mark is on the wire
Increase the weight and increments and record the distance of the wire each time, then find the extension and use the young modulus formula to find the young modulus .

29
Q

On a stress strain graph for the wire in the young modulus experiment, which represents the young modulus

A

The gradient of the graph represents the young modulus as it is stress over strain stresses on the Y axis

30
Q

What is an equation, linking energy, stress and strain and how is it derived?

A

The area under a stress strain graph is the elastic potential energy per unit volume. Therefore we can use the equation energy per unit volume equals to half times stress times strain.

31
Q

State Hook law

A

Force is directly proportional to extension provided it does not exceed elastic limit

32
Q

A stress strain graph for the material X is a straight line through the origin with a breaking point. There is no curve describe the property of this material.

A

Since it has no curve, then it is a brittle material at it breaks abruptly
There is no plastic deformation therefore it is elastic as there is no curve
The material obeys hook law

33
Q

A stress strain graph for the material Y is a hysteresis graph this is when the gradient of the loading is greater than the gradient of the unloading part of the graph states the properties of this material

A

This material is a polymer, as it is a rubber graph. It is elastic as there is no plastic deformation and the graph does not obey hook law.

34
Q

A stress strain graph for a wire is a straight line through the graph from point A up until point. B, which is when it starts to curve until point B graph is obeying hook law what will happen to the section of A to bwhen the sample of the same wire is twice, the original length used.

A

There will be no change as the gradient would be the same. This is because the modulus of the material would be the same and the gradient under a stress graph is the young modulus.

35
Q

A stress drain graph for rubber is given describe the main physical properties of this material

A

So it is a polymer, and it is elastic
Graph does not obey hook law, or the material doesn’t obey hook law
And the loading and unloading parts of the graph are different gradients

36
Q

What were the stress and strain graph look like if the material is stiff and difficult to stretch or compress

A

There will be a larger gradient as these materials usually have large young modulus

37
Q

What will a stress and strain graph look like if the material is very strong

A

There will be a high breaking stress, so the Wyker wouldn’t would be very high

38
Q

Define elasticity

A

The property, which all allows a body to return to its original shape once the load causing deformation has been removed

39
Q

Explain the difference between compressive and tensile forces

A

Compressive forces are the forces that result in a material to be compressed
10 of forces are the forces that result in springs to be stretched

40
Q

What is meant by the spring constant

A

The four supplied per unit extension

41
Q

Explain the difference between two springs A and B when a has A greater spring constant than B

A

He has a greater spring constant. Therefore, it will be stiffer than B as it has a greater gradient.

42
Q

Define elastic deformation

A

In elastic deformation, the extension or compression is directly proportional to force when the elastic limit is not met, and it is a reversible change in an object shape. It is caused by compressive or tense of forces.

43
Q

What is meant by the elastic limit?

A

The applied force which result in plastic deformation

44
Q

Define plastic deformation

A

In plastic deformation, when the applied force is removed, the material will not return to its original shape

45
Q

Define a ductile material

A

A ductile material can be drawn into long wires and still stay strong. An example of a ductile material is copper.

46
Q

Define brittle

A

A material which shows elastic behaviour up to its breaking point when it snaps suddenly, and it does not have any plastic deformation. An example of this is glass.

47
Q

What is a polymeric material, and given example

A

A polymeric material is a polymer, which is made up of long chains, and they behave differently, depending on the temperature, and then molecular structure to examples is polythene and rubber

48
Q

A bridge is being built and the engineer needs to choose the right material for the suspension cables, using his knowledge of young modulus state and explain whether a high or young modulus is required for the suspension cab

A

The suspension cables need to have a high young modular, so that it will only slightly deform under elastic loads

49
Q

A student uses a spring and a weight and a clamp to investigate the extension of a spring. However, the student cannot use a larger mass without the spring, plastically deforming they then attached three springs in parallel and are now able to use a larger mass explain why the springs will not become plastically deformed

A

As the springs are placed in parallel, the total force constant of this system is the sum of the force constant of the three springs. Therefore, the system has three times the spring constant of a single spring. This means it is less likely for the springs to exceeded the elastic limit under a larger weight.

50
Q

A student places three springs in parallel for one system and then they placed one spring on its own for another system. The springs are identical. When recording the extension of the springs, they have a percentage uncertainty, which system will have the larger uncertainty and explain why.

A

The system with three springs will have a larger percentage uncertainty. This is because as the three springs are placed in parallel, the spring constant increases. Therefore, the extensions of the springs were decreased. However, the absolute uncertainty of every spring will stay the same. This means a larger uncertainty is that being divided by eight smaller extensions, which leads to a larger outcome.

51
Q

A student carries out an experiment to determine the young modulus of a thin wire. They measure the tense of stress. However, they have uncertainties explain changes the student could make to decrease this uncertainty.

A

Tensile stress is equal to the fourth divided by the area
Therefore to reduce the uncertainty of tensile stress, we can reduce the uncertainty of the force and area to do this. We can use an accurate balance to weigh masses with a higher resolution. We can also use a micrometre to find the diameter of the wire. This will reduce uncertainty of the cross-sectional area.

52
Q

Wires of the same material are used to make a cable, cable one has less wires. However cable two has multiple wires together. Which cable to have a higher modulus. Explain your answer.

A

No, why are you will not have a higher modulus as young modulus is a property of the material and it does not depend on the size or shape of the material. Therefore, the young modulus will remain unchanged.

53
Q

Describe the difference between the limit of proportionality and the elastic limit of a material

A

Before the elastic and the limit of proportionality, the force will be directly proportional to extension for the material. However, after the limit of proportionality is reached force may not be directly proportional to extension for all points before the elastic limit.

54
Q

The graph of a ductile material is given it has points XYZ on the graph in that order. Describe how the materials behaviour changes as stress increases. And explain how these properties make it suitable for production of thin wires.

A

X is the limit of proportionality and up two point X the young modulus of the material is constant. Therefore the material obeys hooks law up until point why the material is still elastic however past point. X. The material does no longer a base hooks law city graph starts to curveand the material begins to be plastically deformed at point Y at point Z which is the yield point the metal will suddenly stretch without any extra loot. This means small increases of stress will result to a large increase of strain. This is because the natural is ductile, these properties are good for wires as a small increase of force will lead to a large increase in extension.

55
Q

Stress is plotted against strain and a line of Best fit is drawn for a material graph. The graph Also has the 2 lines of worst fit with one with a higher gradient and one with a lower ingredient. How can you figure out the percentage uncertainty from this

A

First, calculate the gradient of the highest line of Worst fit, and then the lowest line of worst fit. Then determine which gradient is higher use the higher gradient. Then to calculate the uncertainty from this use the line of worst fits gradient and substract the line of best fit of the original line
Then, to find the percentage uncertainty to divide the answer by the gradient of the original line and multiplied by 100

56
Q

What is are the units for k (spring constant)

A

Nm^-1

physics alevel (theory) (22 decks)

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