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Volume of a spring

  1. Oct 19, 2010 #1
    Hi

    I am new to the mechanics and material stuff Can anybody tell me that wheather the volume of a spring( Spiral coil ) cahnges with compresson or decompression or not ?
     
  2. jcsd
  3. Oct 19, 2010 #2
    If you mean the volume of the coil of material forming the spring then no.

    I may be looking at this wrongly but the expansion / compression of the outer / inner edges of the spring should be equal and so no volume change occurs.
     
  4. Oct 19, 2010 #3
    Ya i was thinking of the same thing, but can we somehow prove it mathematically or with some simulation software that actually this is the case that there is no volume change
     
  5. Oct 19, 2010 #4
    I've only really used solidworks for modelling, not sure if you can do it in there.

    Why do you need to do this?

    Here is another similar thread you may be interested in, it will save having a to repeat past topics:

    https://www.physicsforums.com/showthread.php?t=322910
     
  6. Oct 19, 2010 #5
    humnn, actually i want to put a spring in a airtight chamber witht a known pressure then i want to compress and decomprss to see weather the pressure inside changes or not, and the only way the pressure is going to change keeping all other fcators constant is that the volume of the spring itself varies with compression or decompression
     
  7. Oct 19, 2010 #6
    I wouldn't think you'd get a (noticeable) pressure change due to volume issues with the spring.

    Have a look at the above thread and see what you think. They are talking about virtually exactly the same experiment as you.
     
  8. Oct 19, 2010 #7
    ya i looked at thread and its quiet helpful, maybe i'll be able to prove something using the math
     
  9. Oct 19, 2010 #8
    The volume of the spring material remains constant, it's shape will change slightly. You certainly won't pick up any meaningful results, even if the spring did chagne in volume.

    The experiement itsself is flawed becuase any change in pressure due to expansion of metal will be well below the precision of a commerical pressure probe. Any change in pressure is more likely due to something else.

    You would be better measuring electrical resistance (although even that is likely to be a poor measure) if directly measuring the spring. I'd simply use a strain gauge to measure how the cross section changes along the spring.
     
  10. Oct 19, 2010 #9
    measuring the crossection can certainly help, but the core idea of the experiment is to translate the change into pressure change ! so if not using spring for pressure chnage i still have to go for the same idea maybe using something else.
     
  11. Oct 19, 2010 #10
    Why pressure change though? I agree with Chris, your best bet is electrical resistance but I'm doubtful even that would give you a readable result.
     
  12. Oct 19, 2010 #11
    yes i think i may have to change my idea of sensing the pressure change but am not givving up yet.
     
  13. Oct 19, 2010 #12
    If there's no volume change within the airtight container, you're looking to measure pressure, that only leaves a temperature change.

    Now unless you plan on compressing and decompressing this spring constantly for a fairly long period of time it isn't going to gain enough energy to change the temperature.

    Even if you did somehow manage to get a pressure change, how would you read it without extremely accurate instruments (we're talking better than x10^-5 accuracy here).
     
  14. Oct 19, 2010 #13
    humnn, well that is also a factor to be considered, i think i'll jump to electrcial resistance and start work there
     
  15. Oct 19, 2010 #14
    I'd still say it's a long shot. What exactly is the purpose of such a test? What are you trying to achieve (I don't mean knowing if volume change occurs, but why are you completing this - class project etc)?

    Also, I just thought about this, a change in resistance can be down to many factors, it would produce a result but wouldn't indicate if the volume had changed.
    For a volume change the density of the material has to change. You'd be better off looking at the factors which would cause the density to change in your spring material and then looking into whether or not such conditions arise during compression/extension (within elastic limit).

    Now that would be a good thing to do a project on, it would give you a far more definitive answer.
     
  16. Oct 19, 2010 #15

    Mapes

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    Loaded compression springs are in a state of torsion. Torsion creates shear stress only (as opposed to normal stress). Shear stress causes shear strain. Shear strain is equivalent to a change in shape, not a change in size. Therefore, compression springs do not change in volume when loaded.
     
  17. Oct 19, 2010 #16

    sophiecentaur

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    Whilst we can't exactly say that there's no such thing as an incompressible solid, considering the conditions under which a spring operates, we can treat steel as incompressible.

    If, of course, it gets hot due to hysteresis, then you could expect some expansion.
     
  18. Oct 19, 2010 #17
    Thankyou all of you for your Interest and knowledged insights into the matter. I have worked and found out that the change in volume may not occur with simple compression or stretching in a spring upto a definite noticeable extent.
     
  19. Oct 19, 2010 #18
    With a steel spring, it is, for all practical purposes incompressible within the limits of elastic deformation. Thus, the change in volume is so miniscule your experiment as you've designed it is not likely to produce measurable results.

    Instead of conducting an experiment that's likely beyond the limits of measurability, why not instead get behind the math and leverage the computational power behind a computer?

    All solids have a http://hyperphysics.phy-astr.gsu.edu/hbase/permot3.html" [Broken](K), which is the pressure increase needed to cause a given decrease in volume. Thus, all solids are compressible.

    As explained in the link above, itself taken from Halliday, Resnick, Walker's 5th ed:

    "A common statement is that water is an incompressible fluid. This is not strictly true, as indicated by its finite bulk modulus, but the amount of compression is very small. At the bottom of the Pacific Ocean at a depth of about 4000 meters, the pressure is about 4 x 107 N/m2. Even under this enormous pressure, the fractional volume compression is only about 1.8% and that for steel would be only about 0.025%. So it is fair to say that water is nearly incompressible. Reference: Halliday, Resnick, Walker, 5th Ed. Extended."​
     
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