1. Chapter 11.2 Graphs are a visual representation of trends in data.
Chapter 11 Notes
Chapter 11.2
Graphs are a visual representation of trends in data.

2. Important Terms for this Section
Independent variable
Dependent variable
Best-fit line
Extrapolation
Interpolation
Gradient
intercept
Inversely proportional
Log scales

3. Plotting graphs Title: should include IV and DV
Label axes with quantities and unit
Use available space most effectively
Use sensible linear scales (no uneven jumps)
Plot all points correctly
Best-fit line should be smooth (doesn’t have to go through all points) – shows overall trend
Identify points that don’t agree with trend
Think about whether origin should be included (0,0)

4. Best-fit lines Does not necessarily pass through any plotted points
Can be used to extend the range of measurements (extrapolation)
Straight line uses y=mx+c
y= dependent variable
x= independent variable
m= gradient (slope)
c= intercept on the vertical axis (y-intercept)
Also, m= Δy/Δx

5. Best-fit lines
For a curve, the gradient is the tangent to the curve at that point

6. Errors and Graphs

7. Inversely Proportional
Sometimes data needs to be processed to produce a straight line
Ex: PV are inversely proportional, so P=nRT(1/V)
Would look like: Should look like:

8. Other notes… Graphs without scaled axes = Sketched
These show qualitative trends
Not for use with experimental data
Use excel or other spreadsheet software to plot your graphs!
Use the best-fit equation and R2 value to analyze how closely the line fits

9. Other notes…
Be careful that you are using a best-fit that actually demonstrates the trend of the graph