Let us say we have a 1KG mass that is hung from a hook on the ceiling. If we run a force probe , it shows us a value like 9.8 N. But if we hang the mass using a 5 foot (1.5 m) chain, the force probe shows a slightly higher value like 9.92N. Why is this ?

I thought of tension in the chain, versus the fact that there is no distance between the hook and the mass when it is directly hung. But in the case of the chain, there is a length factor of 5 feet. I am not sure if that is the reason the force probe is showing a higher value. If some one can please help and explain. Thanks.

  • $\begingroup$ The difference would just be the weight of the chain, or am I misunderstanding the setup? $\endgroup$
    – M. Enns
    Mar 9, 2018 at 3:41
  • $\begingroup$ The chain's massless? $\endgroup$ Mar 9, 2018 at 3:41
  • $\begingroup$ Sir, The chain is not massless. My confusion is as follows. The same mass of 1kg is directly attached to a hook, then it is showing 9.8 N. If we use the same hook and attach a metal chain , then it is showing this higher value. The doubt is , will the length of suspension be a factor. Let us say we take another chain or string that is longer, say 10 feet, because at this point the force probe is actually calculating the tension , am I right. So the question is will there be a variation in force, because of the length of the chain? Thank you. $\endgroup$
    – KudmiSubba
    Mar 9, 2018 at 4:07
  • $\begingroup$ What happens if you hang just the chain on the force probe? $\endgroup$
    – Mark H
    Mar 9, 2018 at 5:28
  • 1
    $\begingroup$ If the chain is not massless, then there will be a self weight of the chain because of the tension being different at different points. I guess, the probe is reading the extra value as the self weight if the chain. And if you take a longer chain, but the mass remains the same, then the value shown by the probe won't change $\endgroup$ Mar 9, 2018 at 6:21

1 Answer 1


Summarizing a discussion from the comments: Given your data, I would predict that hanging only the chain from the force sensor would give a force reading of 0.12 newtons, corresponding to a chain mass of about 12 grams. That's a linear mass density of about 8 grams per meter, which is a little heavier than the "massless" strings that my institution uses in our introductory physics laboratories. A less careful experimenter might have just ignored the difference.

The nice thing here is that this is a testable prediction; you can determine whether this is the effect or whether there is something else that changes between your two configurations which you haven't written down in the present version of your question.


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