C6 (Materials)

Question 1

Equation for young modulus

Answer 1

E = stress / strain = Fx/a change in x

N/m^2

Question 2

Equation for stress

Units

Answer 2

Force/ area

N/m^2

Question 3

Strain equation

Answer 3

Change x / x
(Change in length/ o.g length)
Unit less

Question 4

In stress-strain graphs the steeper (higher) the gradient the greater the…

Answer 4

Greater the young modulus

Question 5

In a stress-strain graph what does the ‘P’ stand for?

Answer 5

P is the limit of proportionality, where the linear relationship between stress and strain ends

Question 6

In a stress-strain graph what does the ‘E’ stand for?

Answer 6

Elastic limit

Below the elastic limit the wire would have returned to its original shape

Question 7

In a stress-strain graph what does the ‘Y’ stand for?

Answer 7

Yield point

Where plastic deformation begins. A large increase in strain is seen for a small increase in stress

Question 8

In a stress-strain graph what does the ‘UTS’ stand for?

Answer 8

Ultimate tensile stress

The materials maximum resistance to fracture

Question 9

In a stress-strain graph what does the ‘S’ stand for?

Answer 9

The point where the wire snaps (called breaking stress).

Question 10

Tensile forces

Answer 10

Forces that produce extension

Question 11

Compressive forces

Answer 11

Those that shorten an object

Question 12

When do helical springs undergo tensile deformation

Answer 12

When tensile forces are exerted on it

Question 13

When does a helical spring undergo compressive deformation

Answer 13

When compressive forces are exerted

Question 14

How does the force extension graph look like

Answer 14

A straight like from the origin up to the elastic limit (directly proportional). The linear region where the spring is undergoing elastic deformation (meaning that it will return to its original length). Beyond this point the spring begins to undergo plastic deformation (permanent structural changes).

Question 15

When does Hookes law apply

Answer 15

For forces less than the elastic limit of the spring

Question 16

Hookes law states:

Answer 16

The extension of the spring is directly proportional to the force applied. Only true if the elastic limit isn’t exceeded.

Question 17

For a spring obeying Hookes law, the applied force F is directly proportional to

Answer 17

The extension, x
F directly proportional to x
F=kx

Question 18

In Hookes law what does the constant k stand for

Answer 18

The spring constant

This is the measure of the stiffness of a spring.

Question 19

What else can you use the equation F=kx for

Answer 19

For a compressible spring (x then represents the compression of the spring).

Question 20

In a force-extension how can you find the value of the spring constant, k

Answer 20

The gradient of the linear region

Question 21

Hooke’s law can be applied to almost any object that…

Answer 21

Can be elastically squashed or extended

Question 22

When a material is compressed or extended without going beyond elastic limit, what can happen to the work done on the object

Answer 22

It can be fully recovered

Question 23

If the material has gone through plastic deformation, then what happens to the work done?

Answer 23

So of the work done on the material has gone into moving it’s atoms to new permanent positions, this energy is not recoverable.

Question 24

The work done equation by a force in extending the spring

Answer 24

Work done = force x change in x

Question 25

What is the area underneath a force-extension graph equal to?

Answer 25

Work done

Question 26

What’s the equation for elastic potential energy

Answer 26

E= half Fx

You can also interpret the equation as work done = average force x final extension

Question 27

What’s another equation for elastic potential energy (after substituting hookes law)

Answer 27

E= half kx^2

Question 28

For a given spring E is directly proportional to extension squared. So doubling the extension does what to the extension stored?

Answer 28

Quadruples it

Question 29

Metal wire (loading and unloading graph)

Answer 29

Loading graph follows hookes law until the elastic limit. Unloading graph will be identical for forces less then the elastic limit. However beyond the limit its parallel to the loading graph but not identical.

Question 30

Rubber bands (loading and unloading graph)

Answer 30

Rubber bands do not obey Hookes law. The rubber band will return to its original length after the force is removed (elastic deformation), but the loading and unloading graphs are both covered in a different.

Question 31

Polythene (loading and unloading graph)

Answer 31

A polythene strips don’t obey Hooke’s law. Thin strips of polythene very easy to stretch and they suffer plastic deformation under relatively little force, they do not return to their original size after being stretched.

Question 32

Brittle

Answer 32

Material that fractures with plastic deformation first (just snaps)

Question 33

Strong

Answer 33

Resists both deformation and failure (withstands a lot of force).

Question 34

Ductile

Answer 34

Deforms before it breaks

Question 35

Hard

Answer 35

Resists dents, scratches and other permanent changes under compressive force

Question 36

Weak

Answer 36

Low UTS (opposite to strong)

Question 37

Tough

Answer 37

Can take lots of Kinetic force

Question 38

Soft

Answer 38

Easily dented/ scratched

Question 39

Malleable

Answer 39

Can easily change shape