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Lower Sixth Physics > Materials > Flashcards

Materials Flashcards

1
Q

What is the density of a material?

A

The density of a material is its mass per unit volume

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2
Q

What is unit of density?

A

kgm^-3

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3
Q

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

A

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

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4
Q

What determines whether an object floats or sinks?

A

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

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5
Q

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

A
  • upthrust of the object = weight of fluid displaced
  • therefore, max upthrust = density of fluid * volume of object * g
  • weight of object = density of object * volume of object * g
  • if the object’s density is >, the weight is always > than upthrust
  • object will sink
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6
Q

What shaped objects does Stokes’s Law apply to?

A

Stokes’s Law only applies to small spherical objects

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7
Q

What type of flow is required for Stokes’s Law to apply?

A

Laminar Flow

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8
Q

What does Stokes’s 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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9
Q

State the Stokes’s Law equation

A

F = 6 π η r v
η = viscosity of the fluid
r = radius of sphere
v = speed of the sphere

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10
Q

What is 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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11
Q

What is plastic deformation?

A

An object has undergone plastic deformation if it doesn’t return to its original shape once the deforming forces are removed. It will have permanent deformation

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12
Q

What is Hooke’s Law

A

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

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13
Q

What is the limit of proportionality?

A

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

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14
Q

What is the the elastic limit?

A

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

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15
Q

What is the order of points on the Force extension graph?

A

LopElYp
- limit of proportionality
- elastic limit
- yield point

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16
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

17
Q

Equation for Hooke’s Law

A

F = k Δx
F = force applied (m)
k = stiffness constant
Δx = extension (m)

18
Q

What is mechanical stress?

A

The force experienced by an object per unit area

19
Q

equation for stress

A

Stress = force / cross-sectional area

20
Q

unit for stress

A

Nm^-2

21
Q

equation for strain

A

Strain = change in length / original length

22
Q

unit of strain

A

none, it is a ratio

23
Q

What does the Young Modulus of a material tell you?

A

It shows a measure of how much force is required for a given extension, regardless to the object’s dimensions

24
Q

equation for Young Modulus

A

Young modulus = Stress/Strain

25
Q

unit for Young Modulus

A

Nm^-2

26
Q

What is breaking stress?

A

The maximum stress that an object can withstand before fracturing.

27
Q

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

A

Elastic potential energy

28
Q

two equations used to calculate the energy stored in a spring

A
  • E = 1/2 F Δx
  • E = 1/2 k Δx^2
29
Q

What does the gradient represent on a force-extension graph?

A

the elastic constant

30
Q

What does the area under the graph mean on a force-extension graph?

A

the elastic potential energy stored

31
Q

What is Archimedes’ Principle?

A

When a body is fully or partially submerged in a fluid, it experiences an upthrust equal to the weight of the fluid it has displaced

32
Q

Define brittle

A

A material that fractures without plastic deformation first.

33
Q

Define ductile

A

A material that can withstand large plastic deformation without breaking, this allows these materials to be stretched into long wires.

34
Q

What is laminar flow

A

A state of flow where layers of fluid move together in parallel with little or no mixing between layers.

35
Q

What is turbulent flow?

A

A state of flow where layers of fluid mix together unpredictably causing a chaotic state.

36
Q

What is viscosity?

A

A quantity measuring the internal friction of a fluid, it acts to reduce the flow of a fluid. It is temperature dependent.

Lower Sixth Physics (13 decks)

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