Topic 7 Materials Flashcards
Explain what is meant by turbulent flow [1]
[1] Mixing of layers leading to eddies
Explain why access to a data logger is useful when tensile testing is carried out [2]
[1] Small extensions can be measured accurately
[1] Large data set/ easy processing of data
One assumption when calculating the force required to stretch a single spring [1]
The string obeys Hooke’s Law
Finding work done to stretch spring
-Use area under graph
=1/2 * F * x
Explanation for why the restoring force is less than the loading force [3]
[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
Length of copper wire to be used in an experiment to test Youngs Modulus [1]
[1] 2m -6m
Definition of Ductile, Elastic and Plastic [3]
[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
Definition of brittle [1]
[1] Snaps / cracks b shatters/ breaks without plastic deformation when subjected to a force
Definition of a strong material [1]
[1] Large force/ stress required to break material
Assumption made when calculating breaking force [1]
[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
How to make a material suitable for larger weights [2]
[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
Explain the difference between elastic and plastic behaviour in a metal. You should include references to molecular behaviour in your answer. [3]
[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)
Define the terms stress and strain [1]
[1] Stress = force / area AND strain = extension / original length
Why a metal is tough [2]
[1] Any reference to plastic behaviour
[1] Large area under non-linear part of the graph
Explain what is meant by strong, brittle and plastic deformation [3]
[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
What is meant by the term polymer? [2]
[1] long chain
[1] Of repeating units / of monomers / molecules / atoms
How does flow differ from high viscosity to low viscosity? [1]
[1] Slower (high viscosity) than low viscosity / greater time taken to flow the same distance / flows less distance in the same time
How would you compare viscosities? [1]
[1] measure speed of flow
Explain the properties: tough and strong [3]
[1] Tough: absorbs energy (before breaking)
[1] by plastic deformation
[1] Strong: high(er) stress before breaking
What property could be determined from the gradient of a Force extension graph? [1]
[1] stiffness of the wire
Force extension graph, increase thickness [2]
[1] steeper gradient
[1] more force required to produce the same extension
[1] limit of proportionality at a larger force
State what is meant by the term yield strength [1]
[1] The stress at which plastic deformation begins / beyond elastic region
State what is meant by Hookes Law [1]
[1] Loading force is proportional to extension
Justification of elastic behaviour [1]
[1] proportional line on Force extension graph and hasn’t reached limit of proportionality yet
State definition of upthrust [1]
[1] weight of fluid displaced
What two properties will affect the speed of a sphere’s t.v in a liquid? [2]
[1] density
[1] temperature
What does tough mean? [1]
[1] can withstand dynamic loads / shock/ impact/ repeated deformation
What is meant by the terms: hard, brittle and tough [4]
[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
How can electrons be used to examine the arrangement of atoms [3]
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
State Hooke’s law [2]
[1] force proportional to extension
[1] up to a certain limit of proportionality
A material is stiff on a stress strain graph if it has…[1]
[1] high gradient , therefore large young’s modulus
A material is tough on a stress strain graph if it has..[1]
[1] large area under graph, therefore large energy density
A material is ductile on a stress strain graph if it has a…[1]
[1] greater strain in plastic region
Suggest why drag is much greater than Stokes Law? [1]
[1] Stokes law requires laminar flow and a small spherical object
Explain what is meant by laminar and turbulent flow [2]
[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
Explain how one design for a truck might use less fuel than another? [4]
[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
Explain how an object heated up will rise in a liquid [3]
[1] Upthrust > weight (+drag)
[1] This is because greater volume/mass of liquid displaced
[1] Upthrust increased (and the mass of object remains constant
