Area under curve using Excel question

In summary, the user is trying to find the area under a curve using an equation, but due to the nature of the graph, all values are negative. They are wondering if they should ignore the negative sign and just take the absolute value of the area. This is because the x-axis decreases as the y-axis increases, causing the (A2-A1) value to always be negative. It is agreed that taking the absolute value and summing them would make more sense since area cannot be negative and the graph is above the x-axis.
  • #1
Mpharm
2
0
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.
 
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  • #2
Mpharm said:
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...
 
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Likes Mpharm
  • #3
berkeman said:
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.
 

1. How do I calculate the area under a curve using Excel?

To calculate the area under a curve using Excel, you can use the built-in function called "Integration" under the "Formulas" tab. This function allows you to specify the range of cells that contain the curve data and the independent variable (x) values. Once you have entered the necessary information, the function will calculate the area under the curve and display the result.

2. What is the purpose of calculating the area under a curve?

The area under a curve can provide valuable information about the data it represents. It can be used to determine the total value or quantity of something, such as the total sales of a product over a period of time. It can also be used to analyze trends and patterns in the data, as well as make predictions and comparisons between different sets of data.

3. Can I use Excel to find the area under a curve for any type of data?

Yes, Excel can be used to find the area under a curve for any type of data, as long as the data is represented by a continuous curve. This includes mathematical functions, experimental data, and even real-world data such as stock prices or population growth.

4. How accurate is the area under curve calculation in Excel?

The accuracy of the area under curve calculation in Excel depends on the accuracy of the data and the method used to calculate the area. The built-in Integration function uses numerical methods to approximate the area, so the accuracy may vary depending on the complexity of the curve and the number of data points used.

5. Can I customize the calculation of the area under a curve in Excel?

Yes, there are different methods that can be used to calculate the area under a curve in Excel, such as the Trapezoidal Rule or Simpson's Rule. These methods can provide more accurate results but require additional steps to set up in Excel. You can also adjust the precision or number of decimal places in the calculation to customize the output.

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