Discussion

Often scientists use graphs to display their quantitative observations.  This helps them to see patterns and relationships that exist in the data.  Graphing involves the display of two sets of data that are related to each other such as the distance moved in a car and the time it took to move that distance.  The relationship can often be determined using a graphing model. .   If the time is placed on the horizontal x-axis and the distance moved on the vertical y-axis, the values can be linked by a straight line.  As the time increases, the distance moved also increases.  Since these two increase by the same value (as time doubles, the distance doubles), we say these are directly proportional and the straight line represents this proportionality.   The equation of the line, y = mx + b, and specifically the slope of the line, m, represents this proportionality.