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Graphing Rules One of the most useful methods of discovering the relationship between two sets of data (two variables) is by graphing the results of an experiment in which one quantity is varied, the resultant variation in the second quantity is noted, and all other factors are held constant. Guidelines for Graphing 1. Be Neat. Always use a pencil. 2. Plot the independent variable (the controlled variable) on the X –AXIS (horizontal) and the dependent variable (the result or change due to the variation) on the Y –AXIS (vertical). 3. Chose a scale so that one block on the graph paper = 1, 2, 5, or 10 (never use 3 or 7 or 9 etc.) 4. Scales should be chosen and numbered so the graph covers as much of the paper as possible using the data you have ( you might not always start at zero) 5. Label the graph: tell what the experiment goes with, give quantities represented, and give units. 6. Don’t number every block on the graph paper. Number every 2nd, or 4th or 5th 7. Each point can have an “error circle” in order to allow for errors in plotting or small errors in data 8. Unless there is some specific reason not to do so, draw a smooth line through the points --- don’t go from point to point with small straight lines. If in your judgment it appears as a straight line, the line need not go exactly through each and every point, likewise a smooth curve will not generally connect each and every point. Judgment must be exercised since making the curve follow each point may make bad data appear as good data. On the other hand, good data with real variations may appear and not be recognized if the curve is carelessly plotted as an average. 9. Good judgment must be exercised in applying these rules. Use graph paper to plot the following Data sets. I. Force ( lbs) 0 1 2 3 4 5 6 III. A Rubber Band Being Stretched Stretch (cm) 0.0 0.6 1.2 1.8 2.4 3.0 3.6 Radius ( M ) 6 14 28 36 50 Moving Car Time ( Seconds) 0 1 2 3 4 II. Model Airplane Flying in a Circle Distance ( M ) 0 5 20 45 80 Force on String ( Netwons) 30 25 16 11 2 IV. Boyles Law Pressure ( atm ) 0.1 0.2 0.3 0.5 0.7 1.0 Volume ( L ) 225 110 75 45 32 22