Area under curve using Excel question

[Mpharm]

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.

 

[berkeman]

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.

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...

 

[Mpharm]

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...

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.