Graphing

Graphing

• Representing numerical information in a picture.

• Graph shows a picture of a relationship

-how two processes relate

-what happens when two events occur simultaneously

-how one factor influences another

Parts of a Graph

• Factors plotted along an axis

• Numeric or some measurable term

• Uses a scale• Horizontal = x-axis =

abscissa• Vertical = y-axis =

ordinate

• Independent variable on x-axis (horizontal)

• Variable that you manipulate

• Dependent variable on y-axis (vertical)

• Variable that responds

Types of Graphs

Bar Graphs

- used to compare amounts of the same type of measurement

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Pie Graph

-used to represent percentage data

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Line Graphs

-used for representing data that constantly changes at regular intervals

- may not necessarily show a regular pattern

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Data Table – data collected is organized in a table.

Independent Variable → Goes on X axis →data on left side of data table

Dependent Variable → Goes on Y axis → data on right side of data table

Analyzing a Graph

Relationship is Inversely Proportional

Relationship is Directly Proportional

Line Graphs – Kinds of Relationships

Relationship – steady increase over a period of time

Curve is a straight line ~ since both factors are increasing the relationship is directly proportional

Relationship – increases over period of time until a max is reached and then decreases

Relationship – change over period of time then remains constant

Relationship – no change

Relationship – decrease over a period of time

Relationship – unchanged, decrease, remains constant

Building a Graph

1. Identify the variables2. Determine the range of each variable3. Determine the scale (fill at least 2/3 of

paper)4. Number and label each axis5. Plot the data points6. Draw the graph7. Title the graph (provide a key if needed)

KEY

Draw a graph for this data

Time(min)

Temperature(ºC)

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0.5 1

1.0 2

1.5 11

2.0 23

2.5 36

3.0 46

3.5 53

4.0 60

4.5 72

5.0 78

6.0 88

7.0 100

8.0 100

“Connecting the dots”

• A line of best fit or also called a “best fit line” is a straight line that best represents the data on a scatter plot. 

• This line may pass through some of the points, none of the points, or all of the points.

• It may also be called a "trend" line.

Best Fit Line

Best fit line may not go through the “O” point

• Choose two points that you think will form the line of best fit. 

Using a graph to determine information not directly measured

or calculated.

• Done with line graphs

• Is impossible to measure every point that exists on that line or a distance from either end of the line constructed from the experimental points.

• Use the processes of interpolation and/or extrapolation

• Interpolation –

• The process of obtaining a value from a graph or table that is located between data points plotted or major points given.

• You make a prediction about what would happen at a given point.

• How much money did the student earn after 5 hours?

• Since you know how the experiment worked before and after the point of interest, you have a better chance of making a correct prediction.

• Extrapolation – • The process of obtaining a value from a chart or

graph that extends beyond the given data.

• The “trend” of the data is extended past the last point given and an estimate is made of the value.

• You can predict what would happen beyond the measured data.

• Must be done with caution. You must assume that any variable in the experiment would not greatly change.

• How much money did the student earn after 10 hours?

• Extrapolation may not be very accurate since you are assuming the trend continues outside the boundaries of your data points