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AS Physics > Materials (topic 11) > Flashcards

Materials (topic 11) Flashcards

1
Q

Density (definition)

A

Mass per unit volume

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2
Q

Why are gases much less dense than solids or liquids?

A

Average separation between molecules is greater

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3
Q

How to measure mass/volume for a regular solid

A

mass => top pan balance
Volume => dimensions using vernier calipers or micrometer

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4
Q

How to measure mass/volume for a liquid

A

mass => measure total mass in a cylinder and then take away mass of cylinder
Volume => measure directly from measuring cylinder

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5
Q

How to measure mass/volume for an irregular solid

A

mass => top pan balance
Volume = use thread to fully emerge in eureka can setup

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6
Q

Density of alloys equation

A

(mass of A + mass of B)/total volume

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7
Q

How is the force needed to extend an object related to it’s tension

A

Equal and opposite

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8
Q

What is Hooke’s law?

A

The force needed to stretch a spring is proportional to the extension of the string

F = k x (delta L)

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9
Q

What is k in F = kL?

A

Spring/stiffness constant; larger k means stiffer spring

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10
Q

What can Hooke’s Law sometimes be represented as in exam questions?

A

F = (lambda x delta L) / L

where lambda is the spring modulus

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11
Q

What happens to k when springs are in parallel?

A

Effective k = k(1) + k(2)

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12
Q

What happens to k when springs are in series?

A

Effective 1/k = 1/k(1) + 1/k(2)

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13
Q

In terms of energies, what happens when a stretched spring is suddenly released?

A

Elastic energy (transferred from the work done to stretch the spring) is suddenly transferred to kinetic energy

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14
Q

What does the area under a force/extension graph represent?

A

Elastic potential energy

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15
Q

Elasticity (definition)

A

Ability to regain shape after being deformed or distorted

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16
Q

Tensile deformation (definition)

A

Stretching of an object

17
Q

Compressive deformation

A

Compressing of an object

18
Q

How to test elasticity of materials?

A
  1. hold at upper end and load with hanging weights
  2. use set square to measure extension
  3. draw tension-extension graph
19
Q

How to measure extension of strained wire? (Searle’s apparatus)

A

Micrometer attached to control wire and levelled with test wire. Test wire is loaded to extension so that “spirit level” drops and extension can be measured.

20
Q

Tensile stress (definition)

A

Tension force per unit area (N/m^2)

21
Q

Tensile strain (definition)

A

Extension per unit of original length (ratio - no units)

22
Q

What happens between 0 and the yield point on the stress/strain graph for a wire.

A

Limit of proportionality = stress/strain no longer constant

Elastic limit = wire will no longer return to original shape

Yield point = wire temporarily weakens; local maxima on curve

23
Q

What happen between the yield point and breaking point on the stress/strain graph of a wire?

A

Y2 = plastic flow changes graph shape; local minima

Ultimate tensile stress (UTS) = local maxima; wire loses strength and narrows at weakest point

Breaking stress = wire breaks

24
Q

What is the gradient on a stress/strain curve

A

stiffness (Young’s modulus)

25
Q

Brittle (definition)

A

snaps without noticeable yield

26
Q

Ductile (definition)

A

Can be drawn into a wire, large plastic flow before breaking

27
Q

Strength of material (definition)

A

The maximum tensile stress it can reach (UTS)

28
Q

How does the loading/unloading curve look for a METAL WIRE?

A

Unloading line is parallel to loading line due to permanent extension

29
Q

How does the loading/unloading curve look for a RUBBER BAND?

A

Change in length during loading is greater than unloading for any one tension point. Low limit of proportionality.

30
Q

How does the loading/unloading curve look for a POLYETHENE STRIP?

A

extension during loading is greater than unloading. low limit of proportionality AND A LOT OF PLASTIC DEFORMATION.

31
Q

Strain energy (definition)

A

Work done to deform an object

32
Q

Strain energy for metal wire equation

A

1/2(T x extension)

As long as limit of proportionality is not reached

33
Q

Calculating strain energy for a RUBBER BAND

A

Area between curves - useful energy when unloading

Total area under curve - work done to stretch

34
Q

Calculating strain energy for POLYETHENE

A

Does not regain initial length, hence area between curves represents work done AND internal energy retained

35
Q
A

AS Physics (13 decks)

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