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PHYSICS > SOLIDS UNDER STRESS > Flashcards

SOLIDS UNDER STRESS Flashcards

1
Q

Whose law states that extension of a spring is directly proportional to the force applied?

A

Hooke’s law

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2
Q

When you double the force on a spring what happens to the extension?

A

It doubles

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3
Q

What is the equation given by Hooke’s law?

A

Force = spring constant x extension (F = k x)

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4
Q

What does k represent in Hooke’s law?

A

spring constant

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5
Q

What does it mean if a spring has a high spring constant?

A

Very stiff

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6
Q

What unit is used for spring constant?

A

Nm⁻¹ or Ncm⁻¹

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7
Q

How do you find the extension of a spring?

A

Extension = Stretched length - Original length

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8
Q

How can you find the work done in stretching a spring?

A

Area under force-extension graph (W=1/2 F x)

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9
Q

What does the gradient (steepness) of a force-extension graph represent?

A

Spring constant

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10
Q

What are the 3 types of solid?

A

Crystalline, Amorphous and Polymers

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11
Q

What is the definition of a crystal?

A

Solid in which atoms are arranged in a regular array with long range order

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12
Q

What is the definition of a crystalline solid?

A

Solid consisting of a crystals with short and long range order

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13
Q

Give 2 examples of crystalline solids

A

Metals (polycrystalline) and Quartz

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14
Q

What is the definition of an amorphous solid?

A

Atoms arranged randomly. No long range order

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15
Q

Give 2 examples of amorphous solids

A

Brick and Glass

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16
Q

What is the definition of a polymeric solid?

A

Solid made up of chain-like molecules

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17
Q

Give 2 examples of polymers

A

Rubber and Nylon

18
Q

What is the definition of a ductile material?

A

A material that can be drawn out into a wire

19
Q

What is the difference between plastic and elastic materials?

A

Elastic materials return to original size and shape when a force is removed, Plastic materials are permanently deformed

20
Q

Sketch the stress-strain graph for a crystalline material

A

Straight line then curve. Elastic limit, elastic and plastic regions labelled.

21
Q

What is another name for a ductile fracture?

A

Necking

22
Q

What type of deformation do crystalline materials undergo?

A

Plastic deformation (necking)

23
Q

How can metals be strengthened?

A

Smaller grains or introducing foreign atoms

24
Q

Sketch the stress-strain graph for an amorphous material

A

Straight line. Elastic region only.

25
Q

What type of fracture does an amorphous material undergo?

A

Brittle fracture / Crack propagation

26
Q

How fast can cracks propagate in amorphous materials?

A

Speed of sound

27
Q

How can amorphous materials be strengthened?

A

Reduce imperfections (thin fibres) or put under compression (pre-stressed concrete)

28
Q

Sketch the stress-strain graph for a polymeric material

A

Steep straight line, long flat line, steep straight line

29
Q

Why is it hard to stretch a rubber band initially?

A

Van der Waals forces act over short distances to keep the molecules stuck together

30
Q

Why is it easy to stretch a rubber band after the initial section?

A

Molecule untangles and straightens out

31
Q

Why is it hard to stretch a rubber band in the final section?

A

Stretching/breaking strong covalent bonds requires a lot of force

32
Q

What is elastic hysteresis?

A

When the graphs of increasing and decreasing stress form a loop

33
Q

What is the area inside a hysteresis curve equal to?

A

Work done

34
Q

How can polymers be strengthened?

A

Cross-links (e.g. vulcanized rubber)

35
Q

What is stress?

A

Stress = Force / Area (σ = F/A)

36
Q

What are the units of stress?

A

Pa or Nm⁻²

37
Q

What is strain?

A

Strain = extension/original length (ε = Δl/l)

38
Q

What are the units of strain?

A

None

39
Q

What is Young modulus?

A

Young modulus = stress/strain (E = σ/ε)

40
Q

What are the units of Young modulus?

A

Pa or Nm⁻²

PHYSICS (11 decks)

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