Materials (UNFINISHED)

Question 1

Density =

Answer 1

Mass / volume

Question 2

Density

Answer 2

Mass per unit volume

Question 3

Volume of a sphere

Answer 3

4/3 pi x r^3

Question 4

Volume of a cylinder

Answer 4

pi x r^2 x l

Question 5

Hooke’s Law

Answer 5

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

Question 6

Hooke’s Law equation

Answer 6

Force = Spring constant x Extension

Question 7

Spring constant

Answer 7

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

Question 8

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

Answer 8

Straight line through the origin

Question 9

Limit of proportionality

Answer 9

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

Question 10

What does the limit of proportionality look like on a graph

Answer 10

Where the line starts to curve (flatten out)

Question 11

Elastic limit

Answer 11

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

Question 12

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

Answer 12

After the limit of proportionality

Question 13

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

Answer 13

The spring constant

Question 14

Tensile forces

Answer 14

Forces which stretch the object

Question 15

Tensile stress

Answer 15

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

Question 16

Tensile stress (sigma) =

Answer 16

Force applied / cross-sectional area

Question 17

Ultimate tensile stress

Answer 17

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

Question 18

Units for tensile stress

Answer 18

Pa

Question 19

Tensile strain

Answer 19

Extension per unit length

Question 20

Tensile strain =

Answer 20

Change in length / Original length

Question 21

Why does strain have no units

Answer 21

Because it is a ratio of lengths

Question 22

What do stress-strain curves describe

Answer 22

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

Question 23

Yield stress

Answer 23

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

Question 24

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

Answer 24

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

Question 25

Breaking point

Answer 25

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

Question 26

Elastic region

Answer 26

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

Question 27

Plastic region

Answer 27

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.

Question 28

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

Answer 28

1/2 x Force x Change in Length

Question 29

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

Answer 29

Work done

Question 30

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

Answer 30

It is ALL stored as elastic strain energy

Question 31

What is the second equation for elastic strain energy

Answer 31

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

Question 32

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

Answer 32

Stress increases

Question 33

Breaking stress

Answer 33

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

Question 34

When is a material considered ductile

Answer 34

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

Question 35

Examples of a ductile material

Answer 35

Copper

Question 36

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

Answer 36

Kinetic energy and Gravitation potential energy

Question 37

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

Answer 37

Only KE

Question 38

Elastic deformation

Answer 38

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

Question 39

Plastic deformation

Answer 39

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

Question 40

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

Answer 40

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

Question 41

Brittle materials

Answer 41

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

Question 42

Ductile materials

Answer 42

Larger plastic region e.g. rubber and copper

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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

Question 45

What does the area between loading and unloading line represent

Answer 45

Work done to permanently deform the wire

Question 46

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

Answer 46

Plastic deformation

Question 47

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

Answer 47

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

Question 48

How is energy conserved when a car goes over a bump

Answer 48

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

Question 49

What is the Young Modulus

Answer 49

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

Question 50

Why is the Young Modulus useful

Answer 50

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

Question 51

Definition of Young Modulus

Answer 51

Ratio of tensile stress and tensile strain

Question 52

Young modulus =

Answer 52

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

Question 53

Gradient of a linear stress-strain graph

Answer 53

young's modulus

Question 54

Area under linear stress-strain graph

Answer 54

Energy stored per unit volume