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ALevel Physics NEW > Section 5 - Materials > Flashcards

Section 5 - Materials Flashcards

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1
Q

What is density?

A

Mass per unit volume

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2
Q

Does density vary with size or shape?

A

Neither

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3
Q

What is the density of water?

A

1gcm cubed

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4
Q

What does Hooke’s law say?

A

Extension is proportional to force

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5
Q

What do tensile forces do?

A

Stretch the spring

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6
Q

What do compressive forces do?

A

Squash the spring

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7
Q

When does Hooke’s law stop working?

A

When the force exceeds the limit of proportionality

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8
Q

What is the equation for Hooke’s law?

A

F = k delta L

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9
Q

What is elastic deformation?

A

The material returns to its original shape and size

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10
Q

What is plastic deformation?

A

The material is permanently stretched

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11
Q

What happens to atoms in a material when it is put under tension in elastic deformation ?

A

The atoms are pulled apart from each other

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12
Q

What happens to atoms after the load is removed in elastic deformation?

A

They return to their equilibrium distance part

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13
Q

Is energy conserved while stretching?

A

Yes

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14
Q

Is elastic deformation, what is the work done stored as?

A

Elastic strain energy

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15
Q

What happens in elastic deformation after the stretching force is removed in terms of energy?

A

The elastic strain energy is transferred into other forms

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16
Q

In plastic deformation, what is the work done stored as?

A

Energy is not stored as strain energy. Work is done to separate atoms

17
Q

In terms of energy is transferred, why are crumple zones good?

A

Some energy goes into changing the shape of the vehicle’s body as it deforms plastically, so less energy is transferred to the people inside

18
Q

What does a stress cause?

A

A strain

19
Q

What is the material called when a force can stretch it?

A

Tensile

20
Q

What is the material called when a force cannot stretch it?

A

Compressive

21
Q

Define tensile strain

A

The change in length divided by the original length of the material

22
Q

Define tensile stress

A

Force applied divided by the cross-sectional area

23
Q

What is the unit of strain?

A

It has no unit

24
Q

What is the unit of stress?

A

N/m^2

25
Q

What is breaking stress?

A

A stress big enough to break the material

26
Q

What is the UTS on a graph?

A

The ultimate tensile stress, the max stress that a material can withstand

27
Q

Describe the stress-strain graph for a material where the force is constantly increasing

A

Straight line through the origin, then starting to curve as it exceeds limit of proportionality, then UTS where the curve starts going down

28
Q

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

A

Elastic strain energy

29
Q

What is the Young’s Modulus?

A

Stress/strain

30
Q

What is the unit of Young’s Modulus?

A

N/m^2

31
Q

What does Young’s Modulus measure?

A

The stiffness of a material

32
Q

Describe the experiment for Young’s Modulus

A
  • Get a long and thin wire
  • Measure cross-sectional area multiple times and average
  • Clamp wire to bench and add weights
  • Measure distance between fixed end of wire and marker
  • As weight increases the marker moves
  • Increase weight in steps
  • Calculate stressStrain using FL/A delta L
33
Q

What does the gradient of a stress-strain graph give?

A

Young’s Modulus

34
Q

What are the 3 important points on a stress-strain graph?

A
  • P is the limit of proportionality (when the graph is no longer a straight line)
  • Below P is the straight line through the origin which shows that the material is obeying Hooke’s Law
  • E is the elastic limit, where the material starts to behave plastically
  • Y is the yield point where the material stretches without any extra load
35
Q

What type of line do you get for a brittle material on a stress-strain graph?

A

Straight line (no curves)

36
Q

Describe the stress-strain graph for a BRITTLE material where the force is constantly increasing

A

Straight line through the origin to show the material is obeying Hooke’s law, then a sudden break in the material as it doesn’t deform plastically

37
Q

What is the difference between a force-extension graph and a stress-strain graph?

A

F-E - specific for the tested object and depend on its dimensions
S-S - Describe general behaviour of material, as stress and strain are independent of dimensions

38
Q

Describe the stages for a force-extension graph for a material where the force is constantly increasing

A
  • Straight line through origin
  • Starts to curve when material exceeds elastic limit, and curves even more when the material starts to plastically deform
  • When load is removed, unloading line is parallel to loading line
  • Unloading line finishes at 0 force, but a longer extension as the material has been permanently stretched
39
Q

What does the area between a loading and unloading line on a force-extension graph represent?

A

Work done to permanently deform a wire

ALevel Physics NEW (12 decks)

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