Materials

Question 1

What is density?

Answer 1

A measure of how much mass an object has per unit of volume

Question 2

When might a high density be needed?

Answer 2

When trying to strengthen things such as buildings

Question 3

When might a low density be needed?

Answer 3

When trying to lighten things or insulate them such as air balloons or foam packaging

Question 4

What is an alloy?

Answer 4

It is a mixture of a metal with other elements to help improve its properties

Question 5

Why are alloys created?

Answer 5

To make metals stronger, harder, more resistant to corrosion, or to change their appearence

Question 6

What is Hooke’s law?

Answer 6

It states that the extension of a spring is directly proportional to the force being applied, as long as the elastic limit is not exceeded

Question 7

What does a large spring constant mean?

Answer 7

It means the spring is stiff, so a large force is required to produce a small extension

Question 8

How do springs add up in series?

Answer 8

1/Ktotal = 1/K1 + 1/K2+…

Question 9

How do springs add up in parallel?

Answer 9

Ktotal = K1 + K2 +…

Question 10

What is tensile stress?

Answer 10

The force applied per unit of cross-sectional area of a material (measured in N/m^2 or Pa)

Question 11

What is tensile strain?

Answer 11

The extension/change in length divided by the original length (it has no units)

Question 12

Describe material that has a large stress and a small strain

Answer 12

It requires a large force for a small extension, so the material is strong and stiff

Question 13

Describe a material that has a large strain and a small stress

Answer 13

It requires a small force for a large extension, so the material is flexible and ductile

Question 14

What is elastic strain energy?

Answer 14

The energy stored in a material (like a spring) when it is stretched or compressed, as long as it stays within the elastic limit

Question 15

What does the area under a force-extension graph show?

Answer 15

Elastic strain energy per unit volume

Question 16

What is meant by elastic limit?

Answer 16

The point beyond which the material will no longer return to its original shape once the force is removed, this means permanent deformation begins

Question 17

What is plastic behaviour?

Answer 17

When a material permanently deform after a force is applied it enters a plastic region where it no longer returns to its original shape

Question 18

What is the yeild point?

Answer 18

The point where a material suddenly stretches with little or no extra force (after this point plastic deformation happens easily)

Question 19

What is necking?

Answer 19

When a material under tension starts to narrow at a specific point just before it breaks

Question 20

What is ultimate tensile stress (UTS)?

Answer 20

The maximum stress that a material can withstand before necking begins (the maximum stress a material can withstand)

Question 21

What is breaking stress?

Answer 21

The stress at which a material finally breaks and separates into two peices (fractures)

Question 22

What does it mean for a material to be brittle?

Answer 22

The material breaks or fractures with little plastic deformation (it doesn’t stretch much before it breaks)
e.g. glass, chocolate and ceramics

Question 23

Draw a stress-strain graph for a brittle material

Answer 23

Look in booklet for answer

Question 24

What does it mean for a material to be ductile?

Answer 24

The material can undergo significant plastic deformation before breaking or fracturing (it stretches quite a bit before breaking)
e.g. copper, steel and aluminium

Question 25

Draw a stress-strain graph for a ductile material

Answer 25

Look in booklet for answer

Question 26

What is meant by the Young modulus of a material?

Answer 26

A measure of the stiffness of a material (the ratio of tensile stress to tensile strain)

Question 27

What is the significance of the gradient of a stress-strain graph?

Answer 27

It tells you the Young modulus of the material

Question 28

How is energy conserved during the stretching or compressing of a material?

Answer 28

When a spring is stretched work is done on the spring, if the spring is stretched within its elastic limit then the energy is stored by the spring but if it is stretched past its elastic limit then some energy is stored and some is lost (due to heat)

Question 29

What is the significance of the area under a stress-strain graph?

Answer 29

It shows you the elastic strain energy stored per unit volume

Question 30

How is spring energy transformed into kinetic energy?

Answer 30

When a spring is stretched or compressed, the stored elastic strain energy is conserved into kinetic energy as the spring starts to move up and down

Question 31

How is spring energy transformed into gravitational potential energy?

Answer 31

If a spring pushes an object upwards , the elastic strain energy is partly converted into gravitational potential energy as the spring gains height

Question 32

What conservation laws apply when spring energy is transformed?

Answer 32

Energy conservation still applies the total energy remains constant, the spring energy is transferred to other forms (KE and GPE)

Question 33

What is the role of energy conservation in ethical transport design ?

Answer 33

Ethical transport design aims to reduce waste energy to protect the environment, save resources and benefit society

Question 34

How is the value of Young's modulus affected by changing dimensions?

Answer 34

It isn't because young's modulus is a property of a material