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Practical help

  1. Apr 1, 2007 #1
    Sorry i ditched the template but as this is an experimental question i wasnt sure that it was needed.

    FOr Physics i am currently writing up an experiment which i had to do i class, the experiment was based upon finding te spring constants of springs by hanging masses on them and measuring the extension.

    I had recorded the results is a table and am now graphingt them... however i was under the impresseion that the graph (force extension) should be a straight line (gradient giving spring constant) however mine is not.

    My graphy begins with a very high gradient and then turns into a "straightish" line afterwards. Is this simply because te masses to begin with were too small to create a linear like extension of teh spring? or is there something wrong with my graph/prac?

    Thanks for any help, and sorry for ditching the template, also9 sorry for the non technical vocab haha...


    Last edited: Apr 1, 2007
  2. jcsd
  3. Apr 1, 2007 #2

    what was the slope of the line (should be= -k) after things looked right to you, and what was the range of masses where it seemed to behave weirdly. Scan it if you can, otherwise the above should help.
  4. Apr 2, 2007 #3
    hey thanks for the reply,

    Im not sure what the actual slope is, i havent checked the gradient yet lol, but its pretty damn high. Te range of masses were 0.1, 0.2, 0.3, 0.4, 0.5 and 1 Kg's

    They seem to become linear after the first few masses, is that because the force is not great enough to extend the spring properly, and if so how do i overcome that obstacle when writing up my prac? do i just discount them?


  5. Apr 2, 2007 #4
    no, never discount them. anomalous behavior is often where discoveries lie hidden--tho in this instance i'm doubtful anything revolutionary will emerge. Now you can attempt to explain them away with good reasoning, but I guess I still don't have a good sense of which data is the good data.

    Look at this and let us know which curve it looks like if any;
  6. Apr 2, 2007 #5
    hey, my graphs dont really look much like any of those ones.. for the singular springs it is almost like a log graph, as in it is stepp, sorry STEEP!!!, to begin with but then levels off into a straight line (which is what i wanted!!)

    I also had to springs set up in parallel, so te new gradient should hvae benn K1 + K2 = new K, however i got a graph which slightly resembled the rubber graph which you supplied (thanks for that)

    Im not sure how u attach documents and so on, if someone could explain this i have all the relevant information in an excel document.

    Thanks again,

  7. Apr 2, 2007 #6
    well from my reading Hookean is only relevant over a narrow range of displacement, it by flat you mean a horizontal line, I would say at this point you're out of the zone and the Steep data was the good stuff. assuming you're plotting mass on y and displacement on x
  8. Apr 3, 2007 #7
    i never said taht the graph was flat, i said it went into a straight line, or at least "straightish".

    I dont really know what is going on with it but it is my suspiscion that the masses i used to begin with i.i the 0.1's and 0.2's were not massive enough, and thus did not apply a high enough force on the spring to get the actual spring constant, instead the spring was barely stretched and i measured that small distance?

    is this correct?
  9. Apr 3, 2007 #8
    who knows? springs tend to be more linear under small displacements, and unless you have really small weights for the spring constant in question, or poor resolution, or both... its just crappy science,
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