Graphing Guidelines
Often the goal of an experiment is to find the relationship between two variables. As one variable changes, so does the other. Graphing is a useful way to visualize and describe these relationships. Because the use of graphs is so common in sciences, it is important for you to know how to construct and interpret graphs. When preparing graphs for this class, keep the following guidelines in mind:
Graphing Guidelines
1. It is done on graph paper. 2. Use the x-axis for the independent variable (the variable changed by the experimenter) and the y-axis for the dependent variable (the variable being measured). 3. The scale you select should be easy to work with such as one square represents 1, 2, 5, or 10 or five squares represents a unit of 1, 10, or a multiple of ten (20, 100, 0.1). Never change the scale along an axis. However, you may use a different scale for each axis.
Graphing Guidelines
4. Select a scale that uses the greatest portion of the paper. Leave enough room to title your axis and graph. 5. Label what the axes represent by including the measurement and its units. For example: "Length (cm)" or “Time in seconds”
Graphing Guidelines
6. For line graphs, plot your points. Sometimes you will be asked to connect the dots.
• Other times you will be asked to draw the line of best fit. The line should pass as close as possible to each of the points but should not be connected point-to-point. If the relationship appears to be linear, the line of best fit should be a straight line.
Graphing Guidelines
7. Title the graph. Make sure you describe what is represented on the horizontal and vertical axes. 8. If you are plotting more than one curve on the same graph, include a legend that identifies the curves. Use different colors or different types of lines such as solid or dashed lines between them.
Example Graphs
Practice Graphs
Recall that a bar graph is useful for comparing information collected by counting. We are going to use the clothing of students in this classroom to demonstrate how to make a data table and bar graph. We will look at the shirt color of boys and girls in the room.
Practice Graphs
Step 1: Gather Data An easy way to organize our data is to create a table. Let’s use this table to fill in our data.
Color Red Black # of Boys # of Girls
Grey
Blue White Multi Other
Practice Graphs
Step 2: Create the Graph
Independent variable (x-axis): ________ Dependent variable (y-axis): __________
Choose two different colors to use (one to represent boys, one to represent girls).
Key Features of Bar Graphs
1. Title 2. Axis are labeled with units 3. Legend
Check your graph to make sure you have these three features
Line Graphs
Recall that line graphs are useful for showing trends. Problem: In an experiment, you check the air temperature at certain hours of the day. At 8 A.M., the temperature is 27 ○C; at 10 A.M., the temperature is 30 ○C; at noon, the temperature is 32 ○C; at 2 P.M., the temperature is 31○C; and at 4 P.M., the temperature is 30 ○C. Graph the results of your experiment.