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I Area under curve using Excel question

  1. Apr 13, 2017 #1
    Hi there,

    I was wondering if someone could help clarify something for me.
    I am using excel to find the area under a curve. I am using the :
    (B1+B2)/2*(A2-A1) equation to do it. However, due to the nature of the graph, all the value I am getting are negative.

    The values on the X axis decrease as the value on the Y axis increase and thus A2- A1 value are always negative giving a negative results to all my values.

    I am wondering, do I just ignore the minus sign and just take the number itself as the area under curve?

    The final value I got attained by summation was -3153.

    My apology if the answer is straightforward. I have been away from this area for many years and I am very rusty.
    Thank you in advanced and I do apologise if the thread was not posted in the right section.
  2. jcsd
  3. Apr 13, 2017 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF.

    I would just take the absolute value of each area before summing them into the total running sum... AFAIK, area cannot be negative...
  4. Apr 13, 2017 #3
    Thank you for your welcome.

    The problem arises because of the nature of the graph.

    What is happening in the experiment is that the surface tension of a liquid is being measured as the area is being compressed. Therefore, as area(on x axis) reduces, the surface tension (on y axis) increases. And because of this, the change in the x value i.e (A2-A1) will be negative. Therefore, leading to negative results when we multiple the (B1+B2) by it.

    It seems to me, the negative value can just be ignored because the difference between A2 and A1 is the same regardless of the positive sign.

    Therefore I agree with you, I think I will just take the absolute value and just add them up. It would not make sense for the area to be positive, especially since the graph is above the + x axis.
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