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a level physics > 04 Materials > Flashcards

04 Materials Flashcards

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1
Q

Accuracy definition

A

How close you are to the true value

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2
Q

Sensitivity definition

A

How small a division a piece of equipment can measure to

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3
Q

Precision

A

How similar repeated values are

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4
Q

What causes upthrust

A

Caused by the displacement of water

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5
Q

When an object is submerged in a fluid, what determines the upthrust experienced?

A

The upthrust of a submerged object is equal to the weight of the fluid that it displaces

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6
Q

How to calculate upthrust (equation)

A

Density of fluid x volume in water x acceleration due to gravity (9.81)

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7
Q

What determines whether an object floats or sinks?

A

The balance between the weight and the upthrust of the object. If the weight exceeds the upthrust, the object will sink

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8
Q

Why will a uniform object, with a density greater than that of the liquid, it is submerged in, always sink

A
  • the upthrust of the object will be equal to the weight of the fluid displaced
  • therefore, the maximum upthrust will be equal to the density of the fluid x volume of object x gravitational field strength
  • the weight of the object is equal to the density of the object x volume of object x gravitational field strength
  • if the objects density is greater, the weight will always be greater than the upthrust and the object will sink
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9
Q

What shaped objects does stokes’ law apply to?

A

Stokes’ law only applies to small spherical objects

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10
Q

What type of flow is required for Stokes’ law to apply

A

Laminar flow

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11
Q

What does Stokes’ Law allow you to calculate

A

The viscous drag force that a small spherical object experiences when falling at low speeds through a viscous fluid with Laminar flow

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12
Q

Stokes’ Law equation

A

F=6πηrv
η= the viscosity of the fluid
r= the radius of the sphere
v = the velocity of the sphere
F= frictional force acting on the interface between the fluid and the particle.

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13
Q

What’s elastic deformation

A

An object has undergone elastic deformation if it returns to its original shape once the deforming forces are removed

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14
Q

What is plastic deformation

A

An object has undergone plastic deformation if it no longer returns to its original shape once the deforming forces are removed. It will have permanent deformation

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15
Q

Express Hooke’s Law in words

A

The extension of an elastic object is directly proportional to the force that is applied to it, up to its limit of proportionality

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16
Q

What is the limit of proportionality

A

The point beyond which the force and the extension will no longer be directly proportional to each other - Hooke’s Law is no longer obeyed

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17
Q

What is the elastic limit

A

The point beyond which the object will no longer elastically deform, and will instead deform plastically

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18
Q

State the defining equation for Hooke’s law

A

F = kΔx
F= force applied (N)
K= stiffness constant
Δx = extension (m)

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19
Q

What is mechanical stress

A

The force experienced by an object per unit area

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20
Q

State the equation for stress

A

Stress = F / A
F = the force applied
A = the cross-sectional area

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21
Q

What is the unit for stress

A

Nm^-2

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22
Q

State the equation for strain

A

ΔL / L

ΔL = the change in length
L = original length

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23
Q

What is the unit for strain

A

Strain is a unitless quantity because it is the ratio of 2 lengths

24
Q

What does the Young Modulus of a material tell you

A

A material’s Young Modulus is a measure of how much force is required for a given extension, regardless of the objects dimensions

25
Q

What equation is used to calculate a materials Young Modulus

A

Young Modulus = stress / strain
Which is the gradient of the stress strain graph with strain on the x axis and stress on the y axis

26
Q

What unit is used for a materials Young Modulus

A

Nm^-2

27
Q

What is breaking stress

A

Breaking stress is the maximum stress an object can withstand before fracturing

28
Q

What is the yield point

A

The point beyond which the object will experience a large extension without substantial increase in the force applied
The point at which the amount of stress the material is at causes the wire to begin to plastically the deform

29
Q

What type of energy is stored in an object that has been stretched

A

Elastic potential energy

30
Q

State 2 equations used to calculate the energy stored in a spring

A

E = 1/2 F Δx
E = 1/2 k Δx^2

x = extension

31
Q

What does the gradient and area represent on a force-extension graph

A
  • the gradient of the linear region represents the elastic constant (k)
  • the area is equal to the elastic potential energy stored in the spring
32
Q

Equation to find out the volume an object is submerged

A

Volume submerged = upthrust / (density x g)

33
Q

What does the area under the line of a of a force/extension graph show and which (force or extension) is on the x axis and which is on the y axis

A

Y axis = force
X axis = Extension

The area under the line shows the work done to stretch

34
Q

what does the gradient of a force extension graph represent and define it

A

The spring constant - a measure of the stiffness of the spring

35
Q

Define upthrust

A

the upward force that a liquid or gas exerts on a body floating in it.

36
Q

Derive the equation of a falling object ( Weight = upthrust + drag) to get it equaling terminal velocity

A

V = 2r^2 g (density of object - density of fluid) / 9η

37
Q

During laminar flow, in what way do the fluid layers move

A

Parallel to each other at different speeds

38
Q

Required conditions for stokes law to apply

A

Small
Spherical
Slower speed ( so it doesn’t go into turbulent flow)
Laminar flowing liquid

39
Q

Why does the spherical object for stokes law have to be small

A

If it’s big, the friction between the fluid and the wall will be too big, disrupting, the viscosity

40
Q

Why can you not use work done = f x d when trying to work out the work done in a spring

A

Because the force is not constant

41
Q

Brittle definition

A

Hard but liable to break easily

42
Q

Ductile definition

A

Able to be deformed without losing toughness

43
Q

Polymeric definition

A

A material that is composed of many monomers

44
Q

Describe the shape of a stress strain graph of a brittle object

A

It will reach its elastic limit quickly and can’t go past it for very long

45
Q

Describe the shape of a stress, strain graph of a ductile object

A

It will be able to be past its elastic limit for longer

46
Q

What does the area under a stress strain line represent?

A

Work per unit of volume

47
Q

How do you work out the strength of an object from a stress strain graph?

A

The highest stress on the line

48
Q

what is the effect of temperature on viscosity and why

A

Viscosity will decrease with increased temperature because as particles move more quickly, they interact for shorter time (shorter interactions) reducing internal friction or stress and therefore decreasing viscosity.

49
Q

Where on a graph would you put the limit of proportionality

A

When it just starts to curve

50
Q

Where on a graph would you put the elastic limit

A

Just beyond the limit of proportionality

51
Q

Where on a graph would you put the yield point

A

After this point, it gets much flatter

52
Q

Compare a ductile material to a brittle material

A

The brittle material has only a linear-elastic region before rupture failure while the ductile materials has a linear-elastic region followed by a region in which plasticity engages.

53
Q

What is breaking stress

A

The maximum stress a material can stand before it breaks is called the breaking stress or ultimate tensile stress

54
Q

If the student had used the larger sphere, the equation for viscosity would not have produced the correct answer.
Explain why.

A

• With the large sphere the speed will be greater so Stokes’ law won’t apply
• The flow is turbulent or not laminar

55
Q

How does viscosity change when temperature in a gas increases

A

viscosity of gases increases with an increase in temperature.

a level physics (6 decks)

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