Comparison of quadratic curve fitting

In a [previous post](, I talked about how to plot kinematics data with a spread sheet and how to fit a quadratic function to the data. In the back of my head I remember “Don’t trust Excel”. I seem to recall someone claiming that Excel did not do a proper fit. To test this, I collected some data and used several methods to fit the data:

  • MS Excel’s built in function fitting
  • Using the spread sheet (Excel) to manually calculate the best fit parameters
  • Vernier’s Logger Pro (version 3.6.1)
  • Plot 0.997 – – a program derived from Sci-Plot

I already discussed how to add a quadratic fit in Excel using the built in tools. Perhaps later I will also discuss Logger Pro and Plot. But how do you come up with a function to fit data? The basic idea is to create a quadratic function and vary the parameters such that the deviation of the actual data from the function is minimized. That is much detail as I want to go into except for the following two links that I used:

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Basics: Making graphs with kinematics stuff part II

**pre-reqs**: [kinematics]( *I don’t think you need [part I of this]( if you don’t want*

So, you still want to make a graph with that kinematics data? You think that graphs on paper are too barbaric? Well, if you are ready, you can use a spreadsheet. But be careful. If you don’t know what you are doing, you can cause some damage (much like flying a 747 after reading a blog about it). Speadsheets allow you to do a couple of things.

  • make pretty graphs
  • fit mathematical functions to data

Of course they actually do much more – but you need [“clippy”]( to help you with that.

First, what software do you use? I think most people will immediately go for Microsoft Excel. I have to admit, this is what I use because I am so familiar with it. Many people already have this also. Truthfully, it is a good spreadsheet program (but not perfect). There are some free alternatives:

  • Open Office – I use the Mac OS X variant Neo Office
  • Online spreadsheet like Zoho) or Google Docs. Both of these are fairly useable.
  • Other – like Apple’s spreadsheet or other non-free stuff.
  • A final excellent option is Vernier’s Logger Pro. Although it is not free (nor perfect) it is not too expensive and can be covered by a school site license

For this tutorial, I will show explicitly how to make graphs using MS Excel. I was going to use open office, but in order to fit a polynomial to data, you have to do some more serious stuff. The basic idea is the same no matter what you use.

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Basics: Making graphs with kinematics stuff

**pre reqs:** [kinematics](

Suppose there is some experiment in which you throw a ball up and collect position and time data (with video analysis). What do you do with this data? Your instructor told you to make a graph, but how do you do that?

Here is the fictional data you (or I) collected:


Here is the text file with the data if you want to reproduce the graphs I make here [kinematics data](

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