Graphs

1
Graphs, Vectors, 2D Motion

• Graphs
• and
• Interpretation
• Updated 9/7/07

2
Graphs and Interpretation

• Graphs need
• Main title
• Axis titles and units
• Appropriate scale
• Fit at least half the paper
• Points with error bars
• Best fit line (with a ruler if straight)

3
Graphs and Interpretation

• Best fit lines are drawn on a graph to give the
  best approximate line that falls within all of
  the error bars.
• Error ranges can be shown on a graph by the use
  of error bars (IB see WB p.3).

4
Graphs and Interpretation

• Points plotted on a graph

with a best-fit line
5
Graphs and Interpretation

• Points plotted on a graph with error bars
• the best-fit line should pass through all of the
  rectangles.

6
Graphs and Interpretation

• Gradient (slope) the rise over run of the best
  fit line. Mainly applies to straight lines, but
  may also be the tangent to the line.
• y2 y1
• -----------------
• x2 x1
• Equation of a line y mx b where
• m slope and b y-intercept

7
Graphs and Interpretation

• Graphing Terms
• intercept (y intercept) the point at which the
  best fit line crosses the y axis.
• proportional a straight line graph whose
  intercept is the origin.
• area under the graph the geometric area covered
  by the best fit line.

8
Graphs and Interpretation

• Graphing Terms
• interpolation continuing the line of a graph
  between the measured points.
• extrapolation continuing the line of the graph
  in front of or past the measured points.
• Note Interpolation and extrapolation are not
  appropriate for every graph.

9
Graphs and Interpretation

• If youre not sure what your doing, draw the
  graph by hand. Only use Excel or some other
  graphing program once you have the concepts under
  control.
• For a tutorial on using Excel to draw graphs,
  including error bars and best-fit lines
• Excel Graphing

10
Graphs and Interpretation

• End of
• Graphs and Interpretation