Computing and Graphing

*Exp0 - Plotting Data on a PC *

Introduction

In Physics 191 we use the computer to acquire data from instruments via interface cards and associated software. In addition, we will make extensive use of *Kaleidagraph* [*Kgraph*], a software package for graphing and data analysis. *Kgraph* is a substantial program (its manual is nearly 700 pages!) but is nonetheless extremely easy and intuitive to use. Three major needs that *Kgraph* will address for us are:

1. Making high quality graphs of your data.

2. Algebraic manipulation of numbers, equivalent to a powerful calculator;

3. Curve fitting, i.e., finding the parameters of a theoretical function that best describe your data.

Projects in the first Laboratory Period

In the first lab [Exp0], we will learn how to use *Kgraph* on a PC equipped with the Windows 95 operating system. Your lab report will document the steps that you have followed to carry out the following exercises. It will contain printouts of the graphs that you generate. Since most of the ensuing labs will require *Kgraph* for plotting and analyzing data, this lab report will also serve as your guide for remembering how to do some basic operations.

Exercises

1. Make a folder on your PC with the name c:\phy191\sec[1-6]\exp0. Insert the number of your section in the brackets, e.g., c:\phy191\sec1\exp0. Data from each week’s lab will be kept in a different, consecutively numbered folder.

2. Make a Scatter Plot of (x,y) data points in c:\phy191\samples\data1. Convert the column 1 data, given in ft/hr, to SI units, m/s. Convert the data, given in degrees Celsius, to Kelvins (K). Label the axes of the graph with names and units, e.g., Velocity (m/s), Temperature (K). Give the graph a a title; include your name, section, experiment, and date in the upper right hand corner of the graph. Save the graph and print it on the laserjet printer. Make sure that the graph labels, legends, etc. to not overwrite any significant part of the graph.

3. Make a vertical bar and stacked histogram plot of the file c:\phy191\samples\data2. In a histogram, data points are grouped into bins, with the number of points in each bin represented by the height of the stack or line. Experiment with the effect of changing the bin size. Try menu items Functions/Bin Data and /Statistics. Explain the graphs.

4. Create a least squares fit to data1. Least squares minimizes the square of the error between the original data and the values predicted by an equation believed to describe the data. (a) Apply a linear, second order, and fifth order polynomial function to the data for V vs. T. Plot one set of residuals vs. T on another graph. Make a histogram plot of the residuals. Use "Statistics" to examine the residuals.

**Navigating the ***Kgraph* manual in Exp0

1. Exercise 1. Before starting this Exercise, work through Kbasics, pp. 30-46. Read pp. 70-80 for directions on defining and editing data. See pp. 104-109 for Formula Entry, useful in algebraically manipulating and converting data.

2. Exercise 2. See Sec. 5.7 on "Binning Data", pp. 118-122.

- Exercise 3a. Read pp 276-279 on simple curve fits; also in Kbasics. For 3b, read pp. 282-284.

NOTE: PHY191 will not meet the week of January 16, 1999. However, your lab report must be turned in to your instructor before January 20.

PHY191 Home

Courses Main Page

Physics and Astronomy Home Page