Why do we graph data?

ü To show the relationship between the graphed variables. (Without calculations)

ü To gain interpolated and extrapolated data.

Rules for Graphing

• Label x and y axes. Include units. The independent variable is graphed on the x-axis. The dependent variable on the y-axis.

• Title your graph. (y vs. x will always work if you can’t be more descriptive!)

• Number axes consistently and consecutively. Use > 75% of each axis.

• Plot data with a fine, accurate point. Circle data points so they are easily located.

• Connect data points with a smooth curve or with a line of best fit.

Sample Data for Graphing

# of Boxes Height of Boxes (m) # of Lamps Height of Lamps (m)

1 0.5 1 0.4

2 1.0 2 1.0

3 1.5 3 1.3

4 2.0 4 2.1

5 2.5 5 4.1

6 3.0 6 4.5

If graphed data forms a straight line:

· There is a constant relationship between the variables

· Interpolated and Extrapolated data is reliable

· Data graphed was consistent or uniform

If graphed data does not form a straight line…

• Shows a non-constant (changing) relationship between the variables.

• Interpolated and extrapolated data is unreliable.

• What was graphed was not uniform.

Interpreting the Graphs

1 Which graph would give more reliable interpolated and extrapolated data?

2 If I had 7.5 m of stacked boxes, how many boxes would I have?

3 Approximately how tall would a stack of 7 lamps be?

4 How many boxes could I stack in a room with a 4 m ceiling?