In a [previous post](http://blog.dotphys.net/2008/09/basics-making-graphs-with-kinematics-stuff-part-ii/), 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 – http://plot.micw.eu/ – 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:
Continue reading “Comparison of quadratic curve fitting”
**pre-reqs**: [kinematics](http://blog.dotphys.net/2008/09/basics-kinematics/) *I don’t think you need [part I of this](http://blog.dotphys.net/2008/09/basics-making-graphs-with-kinematics-stuff/) 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”](http://en.wikipedia.org/wiki/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.
Continue reading “Basics: Making graphs with kinematics stuff part II”
**pre reqs:** [kinematics](http://blog.dotphys.net/2008/09/basics-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](http://blog.dotphys.net/kinematics_data.txt)
Continue reading “Basics: Making graphs with kinematics stuff”