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UNIT 5 PHYSICS > C2 Physics > Flashcards

C2 Physics Flashcards

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1
Q

Define density

A

The density of a material is defined as the mass per unit volume of the material

Density (p) ( kg m -2) = mass (m) (kg) / volume (v) (m3)

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2
Q

Define elasticity

A

When a force is applied, it can be deformed but it can return back to its original shape

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3
Q

Define soft

A

Can be easily deformed, cut, bent or pressed

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4
Q

Define flexible

A

Can easily bend without breaaking

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5
Q

Define plastic deformation

A

Permanent change in shape or size after stress exceeds the yield strength. It does not return to original shape.

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6
Q

Ductile

A

Material can be stretched into wires or cables or put under tension without breaking. It is deformed under tensile stress.

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7
Q

Brittle

A

Easily shatters after elastic limit, cant be permanently stretched. Strong under compression, weak under tension.

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8
Q

Malleable

A

When force is applied, can be hammered into shape or extended easily. Not all malleable materials are ductile

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9
Q

Strong

A

Takes a huge amount of force to break/deform.

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10
Q

Hard

A

Able to withstand a high amount of force without deformation or scratching.

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11
Q

Stress Strain Curve

A

Shows relationship between stress and strain by gradually adding weight and measuring deformation.

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12
Q

Elastic limit

A

Point on stress curve where plastic deformation occurs so will not return back to original shape.

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13
Q

Strength

A

Maximum stress the material can bear before material fails (fractures).

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14
Q

Yield point

A

Point where solid material that is being stretched, starts to change permanently.

Point on a stress - strain curve that indicates elastic limit and start of plastic deformation.

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15
Q

Creep

A

Solid material under stress permanently deforms over time, moving at a slow rate. More severe when heat is applied.

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16
Q

Fatigue

A

Progressive and structural damage leading to weakening of a material due to low levels of stress if theres repeated loading and unloading.

17
Q

Elastic Hysterisis

A

The difference between the strain energy needed to generate a given stress in a material and the materials elastic energy at that stress.

E.g. Elastic bands - stretching elastic band transfers kinetic energy to the band. Energy is needed to stretch the bands molecules, which is then stored as thermal energy increasing the temperature.

18
Q

Define Hookes Law

A

The extension produced by a force in a wire or spring, is directly proportional to the force applied, up to the limit of proportionality

Force (f) (N) = spring constant (k) (Nm-3) x extension (change in x) (m)

19
Q

Define strain energy

A

The area under a force / extension graph for an elastic material represents work done in stretching the material

Work done ( W) = 1/2 x Force (F) x change in x

20
Q

Equation to work out tensile stress

A

Stress (Pa) = force (N) / cross sectional area (m2)

21
Q

Equation to work out tensile strain

A

Strain = extension (change in length) (m) / original length (m)

22
Q

Define youngs modulus

A

How difficult it is to change shape of material. Measure of stiffness.

Ratio of stress to strain for a material (how material will behave when force is applied).

YM (Pa or Nm -2) = tensile stress (f/a) (Pa) / tensile strain (e/original l)

  • Always convert to metres
  • High numbers mean stronger
  • equation for area of a circle = pie r squared
23
Q

What does the straight line in the stress - strain curve represent?

A

Shows material is obeying hookes law (straight line thru origin)

24
Q

What is the limit of proportonality?

A

Point where material stops obeying hookes law, point where the line starts to bend. It will return to its original shape if stress is removed.

25
Q

What is the elastic limit?

A

Highest point of stress on a material where it will return back to its original shape.

26
Q

What is yield strength?

A

The point where a material begins to deform permanently.

27
Q

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

A

Stress - strain graphs show general bhv of a material.

Force - extension graphs are specific for tested objects and depends on dimensions.

28
Q

Define ultimate tensile strength

A

Highest stress a material can sustain just before it fails.

29
Q

What happens when a stress strain graph is showing a brittle material?

A

When the stress reaches a certain point, the material suddenly fractures and does not go thru plastic deformation. Straight line.

30
Q

What makes a material malleable and ductile?

A

Atoms are arranged in regular layers and can roll over eachother without breaking bonds.

31
Q

Why do materials like rubber produce heat during elastic hysterisis?

A

Repeatedly stretching and releasing rubber band will cause it to heat up due to hysterisis, this is because the rubber is transferring energy to its molecules, resulting in heating.

32
Q

What happens when a graph is showing a ductile material?

A

Line will start bending as material is undergoing plastic deformation. Line will be up and down.

33
Q

What happens when a graph is showing a strong material?

A

Line will be straight with a tiny bend at the end.

34
Q

What happens when a graph is showing a plastic material?

A

Loading line will start bending almost straightaway, as plastic deformation is seriously occurring.
Then the unloading line will go diagonally straight down

35
Q

What type of material has a large force before fracture?

A

Strong material.

36
Q

What type of material has a small plastic region?

A

Brittle material.

37
Q

What type of material has a large plastic region?

A

Ductile material.

38
Q

What type of material has a steep gradient before limit of proportionality?

A

Stiff material.

39
Q

What happens when a graph is showing an inelastic material?

A

Loading line will stay straight until right at the end
Unloading line will go parallel underneath from where line curved off

UNIT 5 PHYSICS (3 decks)

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