Making a line graph
Independent and dependent variables A line graph shows how a change in one variable influences another variable. The independent variable is the variable you believe might influence another variable. It is often controlled by the experimenter. The dependent variable is the variable that may be influenced by the independent variable. How to graph variables The following example illustrates how to graph variables. An example As a scuba diver goes deeper under water, she has to think about pressure. How does an increase in depth affect the pressure? Pressure is measured in units of atmospheres. You live at Earth’s surface under a pressure of 1 atmosphere. Figure 1.10 shows depth and pressure data. A graph can help you visualize the relationship between the depth of water and pressure. Step 1: choose x and y-axis Depth is the independent variable because we are interested in how it affects pressure. The independent variable always goes on the x-axis of a graph. The dependent variable always goes on the y-axis. In this example, pressure is the dependent variable. Step 2: make a scale To create a scale for a depth versus pressure graph, you first make a scale. The word scale refers to size of something. When talking about a graph, scale refers to how each axis is divided up to fit the range of data values. Use the formula below to make a scale for any graph. Data range ÷ number of boxes on the axis = value per box Suppose your graph has 12 boxes on each axis. Figure 1.11 shows how you would create a scale for the x-axis. Figure 1.11 also shows how you would create a scale y-axis of the graph for depth and pressure. Step 3: plot your data Plot each point by finding the x-value and tracing the graph upward until you get to the right y-value. Make a dot for each point. Draw a smooth curve that shows the pattern of the points (shown below). |
2 Check the scale for each graph element. This applies to both line graphs and bar graphs.
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3 Locate the graph element you want information on.
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4 Read directly up from "August" until you find a dot or a slanting line, on a line graph, or the top of a bar for a bar graph. Then read straight across to the left until you hit the graph's labeled y-axis. Whatever quantity that line intersects with is the measurement for salmon return in August.
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