The Importance of Graphs
    Why are Line Graphs Useful?
                used to display data to show how one variable (the responding variable) changes in response to another variable (the manipulated variable).

     Plotting a Line Graph (see the illustrations on page 37)
        1.  Draw the axes
                    horizontal axis _____________________________  X axis
                    vertical axis     |     y axis

        2.  Label the axes
                write the name of the manipulative variable on the X axis (horizontal axis) and the unit the measurement is in
                write the name of the responding variable on the Y axis (vertical axis) and the unit the measurement is in

        3.  Create a scale
                mark equally-spaced intervals that cover the range of values you will show.  Both scales should begin at ZERO
                the point where the two axes cross is called the origin of the graph -  coordinates of (0,0)
                the coordinate is a pair of numbers used to determine the position of a point on the graph

        4.  Plot the data
                the point showing the location of the intersection of the measurements meet is call a data point

        5.  Draw a line of "best fit"
                a smooth line that reflects the gneral pattern of a graph.
                the data points yields a straght line is called a linear graph

        6.  Add a title
                should identify the variables or relationship shown in the graph

Why Draw a Line of Best Fit?
        data collected might have small measurement errors and inacccuracies
        line of best fit emphasizes the overall trend shown by all the data taken as a whole.
            Tips:
               if the data points seem to follow along a straight line draw a straight line
               include as many data points as possible directly on the line.
               for data points that don't easily fit on the line, try to have the same number of points above the line as below the line

Slope
        definition - the steepness of the graph line
        slope of a graph line tells you how much "y" changes for every change in "x".

                            Slope = rise -  y² - y¹
                                            run    x² - x¹

        if the straight line of a linear grph goes through the origin (0,0) the graph can be expressed as the following equation                                y = kx
                        where as   X is the manipulated variable,  y is the responding variable, and constant k is the slope.

 
Using Graphs to Indentify Trends
        nonlinear graph - data points do not fall along a straight line
 
        Line graphs are powerful tools in science because they allow you to identify trends and make predictions

        Linear trends
                two variables are related
                make predictions

        Nonlinear trends
                data points might fall along a curve
                data points might show rises and leveling off
                data points may show repeating pattern
                each reveals a trend in the data

        No trend
                 indicates no relationship between the two variables.

PLOTTING A LINE GRAPH  PHSchool.com    webcode cgp6023