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IAL Physics > 1.4 Materials > Flashcards

1.4 Materials Flashcards

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1
Q

Fluids

A

A fluid is defined as any substance that can flow and whould normally be a liquid or a gas

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2
Q

Key properties of a fluid

A

Density, temperature, internal energy, pressure

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3
Q

Density

A

Is a measure of the mass per unit of volume of a substance

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4
Q

Density equation

A

Density= mass/ volume

  • Mass is measured in kg
  • Volume is measured in m^3
  • Density is measured in kg/m^3
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5
Q

When does an objet float or sink?

A
  • If an object has a density less than water, it floats
  • If it has the same density as the medium it suspends
  • If an object has a density greater than water, it sinks
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6
Q

Upthrust

A
  • A fluid will exert a force upward on a body if it is partly or wholly submerged within it
  • This difference in pressure between the top and the bottom of the object produces an upward force on it. This is called upthrust.
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7
Q

Archimedes’ Principle

A

The size of the upward force (upthrust) is equal to the weight of the fluid that has been displaced by the object

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8
Q

Upthrust of an object is equal…

A

to the weight of the fluid displaced

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9
Q

Fluid flows in two ways:

A
  • Laminar flow (streamline flow)
  • Turbulent flow
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10
Q

Laminar flow

A

The word laminar means flow in layers, and it is as if there are layers of fluid sliding over each other. In laminar flow, the layers towards the middle tend to flow faster

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11
Q

Turbulent flow

A
  • Turbulent flow occurs at higher velocities or with non streamlined objects
  • The flow lines become unstable and cross
  • Eddies -small whirbools- from where the flow gets mixed up
  • The fluid velocity in any given place changes
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12
Q

Streamlining

A
  • The lines of laminar flow are called streamlines
  • At any point on any one of these stramlines, the velocity of the flow will be constant over time
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13
Q

Viscosity

A
  • Viscosity is a measure of the magnitude of internal friction in a fluid (resistance between adjacent layers in laminar flow)
  • The visosity of a fluid relates to its stickness and thus to its resistance to flow
  • Syrup and engine oil are viscous while runny liwuids hae low viscocities
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14
Q

Viscous drag

A
  • In a fluid, each layer exerts a force of friction on another ‘layer’
  • This frictional force is also present when object moves through a liquid
  • This force is termed viscous drag
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15
Q

Coefficient of viscosity:

A
  • The size of the viscous drag in a fluid depends on the (coefficient of) viscosity of that fluid. The coefficient of viscosity is given the letter η and is measured in Pa s
  • Viscosity is inversly proportional to the rate of flow of a fluid
  • The greater the viscosity, the greater the viscous drag
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15
Q

Viscosity and temperature

A
  • Viscosity is directly related to fluid temperature
  • In general, liquids have a lower coefficient of viscosity of a higher temperature
  • For gases, viscosity increases with temperature
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16
Q

Is viscous drag greater in Turbulent flow or laminar flow?

A

Viscous drag is greater in Turbulent flow to laminar flow

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17
Q

Terminal velocity

A

The velocity reached in a falling object when weight and air resistance are balanced

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18
Q

Viscous drag equation

A

Fd = 6πηrv

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19
Q

Weight equation

A

Weight = upthrust + viscous drag
m(object)g = m(fluid)g + 6πηrv

20
Q

What happens when a force acts on a material?

A
  • Whenever a force acts on a material sample, the sample will be deformed to a different size or shape.
  • If it’s made longer, the force is referred to as tension, and the extra length is known as the extension.
21
Q

Compression

A

For a material being squashed to a smaller size, both the force and decrease in size are called compression.

22
Q

Hooke’s Law:

A
  • Tension or tensile force increases a material’s volume
  • Compression decreases a material’s volume
  • Extension (Δx) is the difference in length in a given direction (is negative for compression)
23
Q

Hooke’s law

A

Hooke’s law states that the force needed to extend a spring is proportional to the extension of the spring

24
Q

Spring/stiffness constant (k)

A

Measures stiffness: it tells you what force (N) is needed for each metre of extension

25
Q

ΔF =

A

kΔx

  • F = Change in force (N)
  • k = spring spring constant in (nm^-1)
  • x = change in length (m)
26
Q

Limit of proportionality

A
  • Limit beyond which Hooke’s law no longer applies. Non-linear extension after this point.
  • A material only obeys Hooke’s Law if it has not passed what is called the limit of proportionality
27
Q

Elastic limit

A

Limit beyond which object no longer returns to original shape. Plastic deformation

28
Q

The yield point

A

Stress or strain value at which a material undergoes a
sudden or large plastic deformation

29
Q

Elastic deformation

A

is a change of shape where the material will return to its original shape when the load is removed

30
Q

Plastic deformation

A

occurs after the elastic limit, it is a change of shape where the material will not return to its original shape when the load is removed

31
Q

Brittle

A

material without plastic deformation or with very small plastic deformation before fracture. (e.g. glass)

32
Q

Ductile

A

material with large plastic deformation before
fracture. (e.g. steel, copper – which can which can be drawn into wire)

33
Q

When two springs are connected in series…

A

the result is essentially a longer and flimsier spring

34
Q

When two springs are connected in parallel…

A

the result is essentially two springs working together

35
Q

Series equation

A

1/Keq = 1/K1 + 1/K2

36
Q

Parallel equation

A

K1 + K2

37
Q

Energy in a spring

A

ΔE = 1/2k(Δx)^2

38
Q

Hysteresis

A

where the extension under a certain load will be different depending on its history of past loads and extension.

39
Q

Hysteresis:

A
  • When we load a natural rubber band, we put in elastic strain energy.
  • When we unload the rubber band, we don’t get as much energy back as we put in.
  • The area X represents the thermal energy dissipated in the material (energy absorbed!)
40
Q

Hysteresis (key fearures):

A
  • The curve for contraction is always below the curve for stretching
  • Energy absorbed will deform elastic strands in the elastomer
  • The area X + Y is the minimum energy required to stretch the material to extension e
  • The area X represents the thermal energy dissipated in the material (energy absorbed!)
41
Q

Do wires obeys Hooke’s Law?

A

Yes, just like a spring. This is because bonds between atoms stretch just like springs

42
Q

Strain energy

A

is the energy stored when a material is under stress.

43
Q

Stress equation

A

stress = force / area

  • Stress is measured in Newtons per square metre (N m-2) or Pascals (Pa).
  • This allows us to take into account the thickness of a wire.
  • The equation for stress is the force per unit area, and so the units are N m−2, or Pascals, the
    same unit as pressure
44
Q

Stress:

A
  • A tensile stress would refer to an extension force and a compressive stress refers to a compressive force.
  • The ultimate tensile stress is the maximum force per original cross-sectional area a wire is able to support until it breaks
45
Q

Strain

A
  • Strain is the extension per unit length
  • Strain = extension / length
  • There are no units to strain
  • Both extension and length must be in metres for the equation to work
46
Q

Young’s Modulus

A

The Young’s Modulus is the measure of the ability of a material to withstand
changes in length with an added load i.e. how stiff a material is (how hard it is to extend) in elastic deformation.

47
Q

Young’s Modulus equation

A

Young modulus = Stress/strain

48
Q

How can Young’s Modulus be worked out of a graph?

A

Young’s Modulus, E, can be
worked out from the gradient of a stress-strain graph.

IAL Physics (5 decks)

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