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let's get physical! > 4. 'cause we are living in a material world and I am a material girl [NTF] > Flashcards

4. 'cause we are living in a material world and I am a material girl [NTF] Flashcards

materials

1
Q

density =

A

mass / volume

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2
Q

archimedes pricipal is…

A

upthrust = weight of fluid displaced

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3
Q

fluid

A

a substance that can flow

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4
Q

density

A

is a measure of the mass per unit volume of a substance.

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5
Q

upthrust

A

is an upwards force on an object caused by the object displacing fluid

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6
Q

hydrometer

A

is an instrument used to determine the density of a fluid

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7
Q

when is viscous drag exerted?

A

when an object is in laminar flow

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8
Q

what does viscous drag depend on?

A

vicousity of fluid
speed of body
surface area

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9
Q

mass

A

the amount of matter in an object

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10
Q

Viscous drag

A

a resistive force acting on an object travelling through a fluid

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11
Q

stokes law

A

F = 6πrηv

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12
Q

units of coefficiant of viscosity, η

A

Nm^-2s or Pas

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13
Q

What does stokes law apply to

A

small spherical objects travellling at slow speeds with laminar flow

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14
Q

viscosity equation proof proof steps.

A
  1. sum of forces W = U + F
  2. W = m(s)g, U = m(f)g, F = 6πrηv
  3. m=ρV
  4. V = 4/3πr^3
  5. cancel like terms in each expression
  6. rearrange for η
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15
Q

uses for stokes law

A

alcohol testing, food, sports, car design, medicine, comestics

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16
Q

How to measure the volume of irregular objects

A

measure how much water it displaces

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17
Q

upthrust is…

A

weight of fluid displaced

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18
Q

Laminar flow properties

A
  • streamlines

- no mixing of layers

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19
Q

Turbulent flow properties

A
  • dissapation of energy
  • eddy currents
  • mixing of layers
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20
Q

What forces act when a material is stretched

A
  • the stretching force

- interatomic forces

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21
Q

Hookes law

A

the force is directly proportional to the extension (and compression)
F = kx

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22
Q

Gradient of a force extension graph

A

the stiffness

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23
Q

limit of proportionality on a force extension graph

A

where the gradient stops being constant

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24
Q

yield point on a force extension graph

A

where the gradient levels out

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25
Q

elastic limit on a force extension graph

A

between the limit of proportionality and yield point

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26
Q

breaking point on a force extension graph

A

where the gradient drops off at the end

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27
Q

elastic deformation

A

material returns to its original shape once the deforming force has been removed

28
Q

plastic deformation

A

material does not return to its original shape once the deforming force ha been removed

29
Q

yield point

A

Where there is a large increase in extension for a small increase in force

30
Q

The steeper the gradient of a force extension graph…

A

the stiffer the object

31
Q

elastic potential energy

A

the work done to stretch a spring

32
Q

calculate elastic potential energy from a force extension graph

A

area underneath the graph (up to the limit of proportionality)

33
Q

elastic potential energy =

A

= 1/2Fx

34
Q

properties of materials

A
  • stiff/flexible
  • elastic/plastic
  • ductile/malleable
  • tough/brittle
35
Q

felxible

A

small force for large extension

36
Q

ductile

A

can be drawn into wires, Produces a large plastic deformation under tension.

37
Q

malleable

A

can be hammered into shape

38
Q

tough

A

absorbs a lot of energy before they snap

39
Q

brittle

A

can’t absorb energy, the crack/shatter immediately

40
Q

How does area effect how much a wire stretches

A
  • thin wires stretch more

- thick wires stretch less

41
Q

tensile stress =

A

= force/area

42
Q

stress unit

A

Pascal

43
Q

difference between stress and pressure

A
  • stress only happens to solids

- pressure applies to a surface stress occur throughout the solid

44
Q

Ultimate tensile stress

A

the measure of strength. Its the stress when a material breaks or yields.

45
Q

Tensile strain =

A

extension / original length

46
Q

unit of strain

A

no unit (its a ratio/ fraction)

47
Q

young modulus =

A

stress/strain

48
Q

young modulus

A

a property of a material that measures how difficult it is to change the shape of a material

49
Q

young modulus unit

A

Pascals

50
Q

find the young modulus experiment

A
  1. measure the diameter of the wire. Measure the original length of the wire.
  2. attach the wire to the desk and thread it over a pulley with hanging masses on the end. Put a sticky label on the wire at the end of the metre ruler.
  3. Add the masses to the hanger and record the distance movement of the sticky marker.
  4. plot extension against the weight (mg). The gradient is equal to length/area*young modulus.
51
Q

area under stress strain graph

A

the energy stored per unit volume

52
Q

hard

A

resistant to indentation/scratching
Or
surface is resistant to plastic deformation

53
Q

stiff

A

large force for small extension

54
Q

high tensile strength

A

undergo a large stress/force before breaking.

55
Q

linear relationship

A

increase in x is constant for fixed increases in y

56
Q

what happens wire a wire passes its limit of proportionality

A

there is a large increase in extension for a small increase in mass. It will no longer return to its original shape as it has been plastically deformed.

57
Q

how to make extension more accurate (5)

A
  • use a pointer on the wire/ masses to make it easier to read
  • read at eye level to avoid parallax
  • use a set square to ensure the rulers vertical
  • wait for extension to finish
  • add masses gently
58
Q

laminar flow

A

where the layers of flow are parallel and do not mix/cross, no abrupt change in speed or direction of flow.

59
Q

turbulent flow

A

where the layers of flow mix forming eddy currents and causing energy to be dissipated. Random changes in speed or direction.

60
Q

F in stokes law

A

viscous drag

61
Q

spring constants in parallel

A

Kt = K1 + K2

62
Q

spring constants in series

A

1/Kt = 1/K1 + 1/K2

63
Q

viscosity equation

A

(2gr^2 (ρs - ρf))/9v

64
Q

finding drag on an object

A

drag = +- upthrust +- weight

measure radius + mass of object & use known densities

65
Q

area under stress strain graph

A

toughness (energy it can absorb before it snaps)

66
Q

compressive strain vs tensile strain

A

compression decreases in length tensile increases in length

let's get physical! (20 decks)

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