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A Level Physicsvme > Chapter 6 Springs > Flashcards

Chapter 6 Springs Flashcards

1
Q

Compressive and tensile forces?

A

Compressive forces give rise to compression , tensile to extension

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2
Q

Describe the force / extension graph for a spring

When elastic or plastic ?

A

1) initially a straight line THROUGH ORIGIN to a point called proportionality limit
2) now I’d you extend beyond this to elastic limit , it won’t extend proportionally, but if you let go, it hasnt deformed yet - STILL ELASTIC DEFORMATION and will go back to 0
3) past the elastic limit, it will deform AND PLASTIC DEFORMATION

So hookes law applies only to the proportionality limit

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3
Q

What is hookes law and derrive equation

What is k? How find on graph

A

Force is directly proportional to extension until the proportional limit

so with a constant this becomes
F= KX

2) k is the gradient
Where k is the spring constant or force constant or stiffness

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4
Q

What is elastic deformation and plastic

A 
Elastic = return to original length when force removed
Plastic = permanent structural changed to the spring and does not return to original lemtbh
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5
Q

What is a definition for K

A

The amount of force needed to stretch by 1 meter

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6
Q

What happens to the spring constant with multiple springs in

  • Parallele
  • series

Importsnt

A

1) you add all the spring constants together = harder to pull

2) it is actually easier to extend if you have in series as Both springs experience the SAME FORCE so it is shared and essentially 1/2 needed
= so like resistance in Parallel, 1/ ktot = 1/ k1 + 1/k2 etc

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7
Q

How to investigate spring constsnts in pag and how to make experiment better

A
  • attach spring to clamp boss clamp stand and secure to bench , and also clamp a meter ruler next to.
  • add masses and see change of length

2) - use a set square to make COMPLETELY VERTICAL
- eye level reduce systematic parallax error
- repeats

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8
Q

What assumptions do you make when calculating potential forced

A

Thst the ELASTIC LIMIT , PROPORTIONALITY LIMIT NOT REACHED

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9
Q

Why is in series force constant halved and in parallel doubled?
Importsnt for series

A

In Series, the same force is Applied across BOTH SPRINGS , so both springs will extend each and total extension will be addition of both and that’s just double . Here, force is transmitted across both

  • both springs extend each
    2) in parallel the force is split equally amongst the springs. That’s why half the force given to each and they will both half extend , giving half extension
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10
Q

What happens to energy and extending , when can it be recovered and when lost

A

Energy can be recovered provided it doesn’t go past the elastic limit, if it does, then energy when let go won’t all be recovered as some was used to deform It as moving atoms into permanent new position

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11
Q

What about work done by a force to a extend something by a certain distance

Derrive all equations then for work done by spring / elastic potential energy

A

Just like before, work done = force x distance = force x extension

This is given by the area of the graph
WD= Area = 1/2 F X x
Now f = KX
So WD= 1/2 KX2 by substituting

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12
Q

What is tensile strain

A

Strain defined by the force applied per unit cross sectional area

= F/ m2 = Nm-2 or pa

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13
Q

What is tensile stress

A

This is a ratio between the new extension and the original length

X/L and has no units —> could be a percentage fraction etc

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14
Q

So what is Young’s modulus? Why do we need another property- can’t we use spring constant? (Essentially what’s wrong with spring constant (2))

A

Spring constant is dependent on two things
- increase length = reduce spring constant
- increase area = increase spring constant
= thus spring constant deadened on size but young modulus is not, it is a property Independenzen

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15
Q

What is Young’s modulus then actually
Equation
Units

A 
A ratio between stress and strain 
Stress / strain 
Sigma / epision
= FL/AX flax 
In Nm-2 or Pam
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16
Q

How young modulus Independent of area and length

A

If strain , x / l are both 1 then they are removed and you just have a property different for different materials

17
Q

Need to clarify what are tensile forces and what are compressive

A

Tensile anything that causes to stretch (such as underside of bridge)

Compress is anything that causes to shorten (such as top of bridge ) question

18
Q

Explain the whole stress strain graph from the first plastic limit , why do they dip rise etc

Think about a wire stretching and properties of an alloy

What is Uts

A

An alloy is a combination of metals of different sized atoms

  • when increasing force from the elastic limit, the material plastically deforms but extends
  • comes to a point where after enough force, the locking aspect of the alloy atoms UNLOCKS. DUE TO THIS UNLOCK, THE ATOMS accelerate as they slip past each other = Y1
  • think about it, if they accelerate, it requires less force to cause that extension. They accelerate for a bit until they lock again . = Y2
  • from Y2 they plastically deform like normal, increase f increase x but at a curved rate as not proportional . This happens until UTS
  • UTS is the point where a material takes maximum stress before it starts to break, thus a material with higher UTS = stronger material
  • past the UTS it starts to dip again, this is called necking and basically wire just extending easily and becoming thinner (think of play doh when strech, it thins fro a bit before snapping)
    As a result the force applied to cause extension decreases, so that’s by there is a dip

Finally you reach breaking point, here the object will snap….

19
Q

Again what is UTS and what makes a material stronger than another

A

UTS is the maximum stress a material can take before it starts to break.

As a result a more strong material has higher UTS

20
Q

Summary graph very brief

A
  • stress strain Hooke law proportional to proportionality limit
  • then elastic deform still not proportionally to elastic limit
  • now plastically deforms until Y1
  • but then drops due to unlocking acceleration to y2
  • then locks again y2 so past this plastically deform again until UTS
  • after UTS necking, reach breaking point and snap
21
Q

How to calculate young modulus from a graph of stress vs strain

A

Stress proportional to strain until proportionality limit , here stress / strain = gradient = young modulus .

22
Q

What do you get by comparing young modulus of other materials

Why do we use young modulus to do this- what special about it

A

The more young modulus, the more stiffer it is. Here we just using advanced form of spring constant that does NOT BE AFFECTED BY AREA OR LENGTH, just a property

Therefore a thin or thick copper wire will have the same young modulus !

23
Q

How to calculate young modulus of a wire in a lab (PAG)

How to make pag better

A
  • set up two wire to be stretched over a table using clamps at both sides . Here run it over A PULLEY TO MINIMISE THE FRICTION
  • then set up a vernier calliper to measure the slight extension on the other side
  • add Mass known quantity and measure extension,
  • now plot graph f against x and find gradient
  • if you know Orginal length and used micrometer to find diameter average , then can manipulate gradient to find E

2) use repeats and pulley

24
Q

What is stress strain graph for just pure metal

A

Same as alloy without dip

25
Q

What is loading and unloading?

Then what are loading and unloading curves and why are they plotted on same graph

A

Adding force and removing force

2) this is just the graph to show extension when loading snd unloading, they plotted because they might not be the same each time …

26
Q

How does loading unloading look like for a wire

A

This is after elastic limit the loading returns and wire is left slightly extended

Unloading is parallel but thus not same, with area in middle the energy needed to plastically extend it

27
Q

Loading unloading for rubber?
What’s going on? How are lines still different but return to same ?
- what is area

What is this graph called

A

Doesnt follow hookes law, yet when you release force, it returns back to its Orginal length = ELASTIC DEFORMATION

  • but loading and unloading are still different, more work is done by force to extend it then when it de extends ?
  • basically thermal energy is released when the Material is loaded and then unloaded. It kind of stored energy until unloading , does it right at the end.
  • this energy released is shown by the area
  • to do with polymer propertied

This is a hysteresis loop

28
Q

Polystyrene load unload?

A

It takes little force to stretch and they suffer plastic deformation straight away, and so final return is further than initial = shows plastic deformation

29
Q

Is plastic deformation always a bad thing?

A

No for example steel being shaped in car needs to retain its plastic deformed shape so we can use it etc

30
Q

What about the stress strain for brittle materials like glass and cast iron?

A

These show proportional elastic extension until its breaking point - they never plastically deform, elastic and then snap

31
Q

Final summary on all materials in chapter

  • ductile metal, pure metal
  • metal wire load vs unload
  • polymers : rubber load vs unload , polythene
  • brittle materials stress vs strain
A
  • ductile dips when unlock and dips after UTS due to neck and the. Breaks
  • pure metal does same thing except first dip
  • metal wire unloads parallel but shows the permanent extension plastic
  • rubber takes more work to extends vs when under ending, this let out as thermal (stores energy)
  • polythene just deforms hella fast , shown by final extension different to initial
  • brittle materials will extend elasticsllt snd break = never plastic
32
Q

IMPORTANT WHAT IS STRAIN DENSITY AND HOW TO FIND ENERGY OF STRESS STRAIN

A

Energy =1/2 fx

Area = strain density which is amount of energy per m-3

33
Q

Why in a wire when deform is grsdient still the same ?

A

Because of extension the force before are still identical between the binds

A Level Physicsvme (49 decks)

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