GraphingGraphing

Why do we use graphs?Why do we use graphs?

It’s an organized way to express data.

Allows for easy interpretation of the data.

Allows for “extrapolation” of data, when necessary.

What does extrapolation mean???

What are the parts of a graph?What are the parts of a graph?

Independent variable:– Goes on “x” (horizontal) axis– Controlled by the experimenter – “I” for I

control the independent variable!

Dependent variable: “D” for Data!!– Goes on “y” (vertical) axis– Result of applying the independent variable

Let’s do a practice problem!

Determining variablesDetermining variablesThe following is a data table gathered by geologists after a volcanic eruption in Hawaii. Geologists were interested how lava affected the temperature of nearby rocks.Based on the table, what is the independent variable and what is the dependent variable?– ANS: IND = time DEP = temp

Time (minutes)

Rock temp (◦ C)

0 30

1 33

2 38

3 40

4 41

5 42

6 43

7 43

8 43

X Y

Setting up your graphSetting up your graph

Now we know the variables, so we know where to plot them.– On X axis (independent)

• Time

– On Y axis (dependent)• Temperature

05

101520253035404550

0 2 4 6 8 10

Time (minutes)

Tem

pera

ture

(C

)

Time (minute

s)

Rock temp

(◦ C)

0 30

1 33

2 38

3 40

4 41

5 42

6 43

7 43

8 43

Plotting Your Data

Interpreting your graphInterpreting your graph

What is the trend in the graph we just plotted?– Temp increases then levels off.

Why did it level off after 6 minutes?– Many reasons; possibly lava began to cool.

Types of relationships determined Types of relationships determined by graphsby graphs

Direct relationship– BOTH variables (x and y) INCREASE– Can you sketch a graph that shows this?

Types of relationships determined Types of relationships determined by graphsby graphs

Indirect relationship:– Independent variable increases, dependent

decreases.– Can you sketch a graph with this relationship?

Types of relationships determined Types of relationships determined by graphsby graphs

Cyclic relationship:– Shows repeating of same event over time– Can you sketch a graph that shows a cyclic

relationship?

Types of relationships determined Types of relationships determined by graphsby graphs

Stable (no change):– Dependent variable stays the same as

independent increases– Can you sketch a graph showing stability?

Comparing rates of change using Comparing rates of change using graphsgraphs

The angle of plotted line tells us the rate– The STEEPER the line, the FASTER the rate– Which of the following graphs has a faster rate?