Module 3.4 - Materials Flashcards

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1
Q

How does energy transfer when stretching a spring then releasing?

A
  1. As you stretch, the pulling force transfer energy to the ELASTIC store
  2. When you release, the energy transfers from the elastic to the KINETIC.
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2
Q

Define deformation

A

The change in shape/size of an object (stretching/squashing/thrusting)

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3
Q

What is elastic deformation?

A

When a material RETURNS to its original length when a load is removed

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4
Q

What is plastic deformation?

A

When a material DOES NOT return to its original length when a load is removed - permanent

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5
Q

Describe extension

A

> Caused by TENSILE forces
Equal and opposite tension forces when stretching
Causes INCREASE in length
POSITIVE extension

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6
Q

Describe compression

A

> Caused by COMPRESSIVE forces
Equal and opposite but facing EACH OTHER
Causes DECREASE in length
NEGATIVE extension

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7
Q

What happens if a object obeys Hooke’s law?

A

Its extension will be DIRECTLY PROPORTIONAL to the force applied to deform it, up to its elastic limit

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8
Q

What is Hooke’s law in equation form?

A

F = kx

F - N
k - N/m
x - m

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9
Q

What does the distance the spring moves whilst stretching equal?

A

The extension of the spring

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10
Q

How do you found the work done of a spring (energy stored) on a F-x graph?

A

The area UNDER the graph

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11
Q

How do you work out the Elastic potential energy, E of a material if it obeys Hooke’s law?

A

E = 1/2Fx = 1/2kx^2

E - J
k - N/m
x - m
F - N

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12
Q

Which - spring, rubber band, plastic strip - has elastic deformation?

A

Spring and rubber band

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13
Q

Which - spring, rubber band, plastic strip - obey’s Hooke’s law

A

Spring

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14
Q

For which - spring, rubber band, plastic strip - does all its energy come back out when unloaded?

A

Spring

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15
Q

Which - spring, rubber band, plastic strip - has plastic deformation?

A

Plastic strip

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16
Q

Which - spring, rubber band, plastic strip - does not obey Hooke’s law?

A

Rubber band and plastic strip

17
Q

For which - spring, rubber band, plastic strip - does some energy remain as thermal?

A

Rubber band and plastic strip

18
Q

For which - spring, rubber band, plastic strip - has some of its energy used to break bonds so doesn’t come back out?

A

Plastic Strip

19
Q

What happens to force and extension for a spring of fixed length and thickness?

A

Force and extension remain DIRECTLY PROPORTIONAL

20
Q

What happens to force and extension as the length of the spring is changed?

A

Force is directly proportional to extension ÷ length - x/L

21
Q

What happens to force and extension as the thickness of the spring is changed as well as length?

A

Force ÷ area is now directly proportional to extension ÷ length

22
Q

How is stress worked out?

A

Stress = Force ÷ area

Stress - N/m^2
Force - N
Area - m^2

23
Q

How is strain worked out?

A

Strain = extension ÷ length of material

Strain - no units
Extension - m
Length - m

24
Q

How do you work out Young’s modulus?

A

E = stress ÷ strain

=  (Force x Length) ÷ (Area x Extension)
25
Q

When is Young’s modulus valid?

A

When the limit of proportionality is not exceeded

26
Q

How do you work out Young’s modulus from a stress-strain graph?

A

The GRADIENT of the ELASTIC region of the graph

27
Q

Define Ultimate tensile stress/strength (UTS)

A

MAXIMUM stress that a material can withstand

28
Q

What is the Breaking stress?

A

The stress at the FRACTURE point

29
Q

Describe a strong material

A

> Can withstand a LARGE FORCE

> HIGH UTS

30
Q

Describe a stiff material

A

> DIFFICULT to bend

> HIGH Young’s Modulus

31
Q

Describe a ductile material

A

> Can be DRAWN out into a WIRE

> Experiences a lot of PLASTIC deformation before snapping

32
Q

Describe a brittle material

A

> Snaps easily

> Experiences NO or LITTLE plastic deformation before snapping

33
Q

Describe a polymeric material

A

> Made of long chain molecules called POLYMERS

> Experiences PLASTIC deformation and NECKS before snapping

34
Q

What does it mean when an object necks?

A

When stress decreases by a greater proportion than strain