1. Graphing
For Science Class

2. Graphs are used to
Show the relationship between variables at a quick glance
Predict unmeasured data
Organize data in a meaningful way

3. The Basics
All graphs in science are scatter graphs (like line graphs but the dots are not connected).
The independent variable is the one that affects the other variable. This variable is usually placed on the X-axis.
The dependent variable is the one that changes due to the independent variable. It is usually placed on the vertical axis (Y-axis).
A line of best fit will be drawn through the plotted points
A line of best fit is a smooth line that does NOT directly connect each dot.

4. Rules for Graphing Always use a ruler to keep your graph neat!
Label both axes with the values and unit.
Use a constant scale on each axis – each mark on one axis should be worth the same amount.
Title your graph – “Independent variable’s effect on dependent variable” or “Independent variable versus dependent variable.”
Draw a line of best fit.
If more than two lines are shown on the graph, use a key to distinguish which line is which.

5. Drawing a Line of Best Fit
The line of best fit does not connect every dot.
The line of best fit shows the general trend of the graph.
It can be used to predict unmeasured data.

6. Predicting Unmeasured Data
Create the line of best fit.
Extend the line of best fit following the same trend.
Anywhere the line has been extended is predicting unmeasured data.
The dotted line shows the line of best fit. By extending the line past the last data point, we can estimate that when the price reaches $30, the sales will be about 160 units per month.

7. Graph with a Direct Relationship
As the x-axis increases, the y-axis increases
The rate of change is constant.

8. Graph with a Inverse Relationship
As the x-axis increases, the y-axis decreases
The rate of change is constant

9. Graph with an Exponential Relationship
As the x-axis increases, the y-axis increases at a faster pace, creating a J shaped graph.
The rate of change is variable.

10. Calculating Slope of a Line
Slope = (y2-y1)/(x2-x1)
The x2 and y2 point should always be further to the right on the graph, even if this gives you a negative slope.
Using one point on the graph for both x1 and y1 (x1=1, y1=5).
Use another point on the graph for both x2 and y2 (x2=4, y2=20).
Slope = (20-5)/(4-1) = 15/3 = 5

11. Use this graph to answer questions #15-20
This graph shows how the growth of plants is affected by the hours of shade.