Time to make a graph?!? Follow these step-by-step instructions, and you are sure to have a graph that will impress even the grouchiest TA.
Step 1: When making a graph on graph paper, it is important to have graph paper with fine enough divisions to give you useful information from your graph. One acceptable type of graph paper is Purdue Form F, available at the bookstores. Not acceptable graph paper includes pages out of your lab notebook or quad-rule paper (4 squares per inch).
Step 2: After selecting a suitable piece of paper, grab a ruler. It is time to draw your axes. You will need a y-axis (up and down) and an x-axis (side to side). Typically, but not always, these will intersect in the lower left corner of your graph paper. Graphs are always Y vs. X. For example a graph of mass vs. volume would have mass on the y-axis and volume on the x-axis.
Take a look at your data. One set of data probably spans a much larger range than the other. You will want to orient your graph paper so that the larger data set will be plotted on the long side of the paper. (Do not be afraid to turn your paper sideways. Your TA is smart and will know which way to hold the graph while looking at it.) Now use that ruler to draw you axes. Don't forget to label them each with a name and proper units.
Step 3: Now that your axes are drawn, you need to divide them properly. Unless you are making a graph on logrithmic paper (if all the squares on your paper are evenly spaced, you are not) it is important to keep the spacing even along the axis. For example, if you decide that 5 squares is .1 cm on the x-axis, then 5 squares must be .1 cm the whole length of the axis. (5 squares = .1 cm, 10 squares = .2 cm, 15 squares = .3 cm... I think you get the point) In order to get the best possible data from your graph, you should spread your values along the axes as far as possible. You bought the whole page, now use it! The last thing to consider in dividing your axes is whether (0,0) is an important and meaningful point in your graph. If it is, then (0,0) should be the intersection of the axes. Otherwise, your axes can intesect wherever it is convenient. Give this a little thought, then grab that pencil and make your divisions.
Step 4: This is an easy one! Add your data points to your graph.
Step 5: Now that you have the data, you need to decide on a shape. The shape is never akindergarten connect-the-dots project. Most likely you need either a line or a curve. (Check your lab manual, it probably will tell you there in case the dots on your graph don't make it obvious). This line or curve does not need to touch every data point on the graph. It should be drawn to be smooth and come close to most of the points.
Step 6: Give your graph a title. No creativity required. A simple Mass vs. Volume type title will certainly sufice. You may want to include the section of the experiment, trial number, or other identifying information as a subtitle.
Step 7: Get whatever information you need from your graph.
Step 8: Check your graph against this list:
In order to get the most accurate slope from a graph, you must first make sure your data is taking up at least 3/4 of the space on the page. After adding the data points to your graph, you will want to draw in either a straight line or a curve. For activity 3, you will use a straight line. This line will never be a connect-the-dots project. Rather, the goal is to get the line to come close to as many of the points as possible.
From this graph, we are trying to determine the density of an unknown substance. First, you know that density is mass divided by volume.
When you made your graph, you plotted volume on the x-axis and mass on the y-axis. The equation for determining the slope is
Thus you have mass divided by volume and the slope of the line is equal to the density.
Next you need to determine the slope of the line. Look at the line you have drawn and choose two places where the line you have drawn crosses a corner of one of the "boxes" on the graph paper. You do NOT want to use your original data points because that would defeat the purpose of drawing a straight line that fits the data! Take the coordinates of these two points and put the data into the slope equation to calculate the slope.
If you have followed all of these steps and made wise decisions along the way, you should now have a graph that is pleasing to the eye, chock full of information, and worth lots of points on your lab report.