Topic 7 Materials

Question 1

Explain what is meant by turbulent flow [1]

Answer 1

[1] Mixing of layers leading to eddies

Question 2

Explain why access to a data logger is useful when tensile testing is carried out [2]

Answer 2

[1] Small extensions can be measured accurately

[1] Large data set/ easy processing of data

Question 3

One assumption when calculating the force required to stretch a single spring [1]

Answer 3

The string obeys Hooke’s Law

Question 4

Finding work done to stretch spring

Answer 4

-Use area under graph

=1/2 * F * x

Question 5

Explanation for why the restoring force is less than the loading force [3]

Answer 5

[1) Energy returned is less than the work done in stretching the cords
[1] Energy must be conserved so internal energy of cords must increase
[1] Rubber cords get warmer

Question 6

Length of copper wire to be used in an experiment to test Youngs Modulus [1]

Answer 6

[1] 2m -6m

Question 7

Definition of Ductile, Elastic and Plastic [3]

Answer 7

[1] Ductile : can be pulled into a long thin shape
[1] Elastic : returns to original shape/size once deforming force removed
[1] Plastic : does not return to original shape/size once deforming force removed

Question 8

Definition of brittle [1]

Answer 8

[1] Snaps / cracks b shatters/ breaks without plastic deformation when subjected to a force

Question 9

Definition of a strong material [1]

Answer 9

[1] Large force/ stress required to break material

Question 10

Assumption made when calculating breaking force [1]

Answer 10

[1] Elastic limit not reached
[1] elastic behaviour
[1] Hooke’s law obeyed
[1] Young Modulus still holds at breaking point
[1] Area remains constant

Question 11

How to make a material suitable for larger weights [2]

Answer 11

[1] Increase area of material, make it thicker
[1] as stiffness would have to be increased/ reference to E=fl/Ax / as it would have to withstand a greater stress / otherwise extension would be much greater

Question 12

Explain the difference between elastic and plastic behaviour in a metal. You should include references to molecular behaviour in your answer. [3]

Answer 12

[1] Plastic =permanent AND elastic = reversible
[1] Elastic : bonds stretch but not broken/ atoms move apart then return
[1] Plastic : bonds broken (when stressed) / atoms do not return to original position (after stress)

Question 13

Define the terms stress and strain [1]

Answer 13

[1] Stress = force / area AND strain = extension / original length

Question 14

Why a metal is tough [2]

Answer 14

[1] Any reference to plastic behaviour

[1] Large area under non-linear part of the graph

Question 15

Explain what is meant by strong, brittle and plastic deformation [3]

Answer 15

[1] Strength - Force/ stress required to break, large force required to break
[1] Brittle- shatters/ snaps/ fractures/ cracks/ breaks with little plastic deformation/ with little strain
[1] Plastic - does not return to original length when deforming force removed

Question 16

What is meant by the term polymer? [2]

Answer 16

[1] long chain

[1] Of repeating units / of monomers / molecules / atoms

Question 17

How does flow differ from high viscosity to low viscosity? [1]

Answer 17

[1] Slower (high viscosity) than low viscosity / greater time taken to flow the same distance / flows less distance in the same time

Question 18

How would you compare viscosities? [1]

Answer 18

[1] measure speed of flow

Question 19

Explain the properties: tough and strong [3]

Answer 19

[1] Tough: absorbs energy (before breaking)
[1] by plastic deformation
[1] Strong: high(er) stress before breaking

Question 20

What property could be determined from the gradient of a Force extension graph? [1]

Answer 20

[1] stiffness of the wire

Question 21

Force extension graph, increase thickness [2]

Answer 21

[1] steeper gradient
[1] more force required to produce the same extension
[1] limit of proportionality at a larger force

Question 22

State what is meant by the term yield strength [1]

Answer 22

[1] The stress at which plastic deformation begins / beyond elastic region

Question 23

State what is meant by Hookes Law [1]

Answer 23

[1] Loading force is proportional to extension

Question 24

Justification of elastic behaviour [1]

Answer 24

[1] proportional line on Force extension graph and hasn’t reached limit of proportionality yet

Question 25

State definition of upthrust [1]

Answer 25

[1] weight of fluid displaced

Question 26

What two properties will affect the speed of a sphere’s t.v in a liquid? [2]

Answer 26

[1] density

[1] temperature

Question 27

What does tough mean? [1]

Answer 27

[1] can withstand dynamic loads / shock/ impact/ repeated deformation

Question 28

What is meant by the terms: hard, brittle and tough [4]

Answer 28

[1] Hard: difficult to scratch and dent
[1] brittle: breaks without plastic deformation/ shatters cracks
[1] Tough: can withstand deformation/ dynamic loads/ shock/ impact
[1] plastic

Question 29

How can electrons be used to examine the arrangement of atoms [3]

Answer 29

any three from

• electrons have wave properties
• beam of electrons directed at the specimen
• electrons diffract by spaces between atoms
• superposing constructively/series of dots seen
• pattern can be used to determine arrangement of atoms
• no (or irregular) pattern indicated an amorphous structure
• pattern seen on a fluorescent screen as electrons hit it

Question 30

State Hooke’s law [2]

Answer 30

[1] force proportional to extension

[1] up to a certain limit of proportionality

Question 31

A material is stiff on a stress strain graph if it has…[1]

Answer 31

[1] high gradient , therefore large young’s modulus

Question 32

A material is tough on a stress strain graph if it has..[1]

Answer 32

[1] large area under graph, therefore large energy density

Question 33

A material is ductile on a stress strain graph if it has a…[1]

Answer 33

[1] greater strain in plastic region

Question 34

Suggest why drag is much greater than Stokes Law? [1]

Answer 34

[1] Stokes law requires laminar flow and a small spherical object

Question 35

Explain what is meant by laminar and turbulent flow [2]

Answer 35

[1] laminar flow is when there is no abrupt change in velocity or mo abrupt change in speed or direction of flow
Or velocity at a point is constant
Or flows in layers/flow-lines/streamlines
Or layers do not mix/cross
[1] Turbulent flow is where layers/flow-lines/streamlines mix
Or contains Eddie currents/vortices/whirlpools
Or abrupt random changes in speed and direction of flow

Question 36

Explain how one design for a truck might use less fuel than another? [4]

Answer 36

[1] New design is more streamline
[1]Reduces turbulent flow with fewer eddy currents
[1] Decreasing air resistance/drag
[1] Less energy transferred to the air Or less power/work/energy needs to be supplied

Question 37

Explain how an object heated up will rise in a liquid [3]

Answer 37

[1] Upthrust > weight (+drag)
[1] This is because greater volume/mass of liquid displaced
[1] Upthrust increased (and the mass of object remains constant