Making Science

Graphs and

Interpreting Data

Eye Opener: 5 mins

•What do you see?

•What do you think?

•Look up terms you

don’t know

What do Graphs Tell You?

• A graph is a way of expressing a

relationship between two different

variables.

• There are several types of graphs

– Bar Graph (Histogram)

– Pie Chart

– Scatterplot

– Line Graph

VariablesEvery scientific investigation has variables:

• Variable: factor that changes in an experiment.

• Independent variable: variable that is manipulated (changed) in an experiment.

• Dependent variable: variable that is measured

Vocabulary

• scale: the relation between the units you are using and their representation on the graph.

• x-axis: horizontal axis (usually represents the independent variable)

• y-axis: vertical axis (usually represents the dependent variable)

• line of best fit: line that best represents the trend between the data points

• trend: a general tendency or direction

• clump (data): grouping data points together

Bar Graph

• A bar graph is used to compare a set of measurements, amounts, or objects.

• Height of bars are proportional to size

• Qualitative, nominal (categorical) data only; discrete & defined objects only

• No scale

Bar Graph (Histogram)

• Special type of bar graph: represents continuous categories

– Data is often clumped to reduce number of data points

– X and y axis has scale

Pie Chart

• A circle graph or pie chart is a divided circle that shows how a part of something relates to the whole.

• Qualitative, nominal data

• Appropriate for six categories or fewer

Creating a Pie ChartHow to create a Pie Chart

1. Draw a circle with a protractor.

2. Convert the measures of the variables into percentages, and divide the circle accordingly. **Relate the percentages to degrees of the circle (360◦)

1. It is best to order the segments clockwise from biggest to smallest, so that the pie chart looks neat and the variable are easy to compare.

3. Write percentage and category labels next to each segment, so that users are not required to refer to the key each time they want to identify a segment.

Scatterplot

• Show relationship between pairs of quantitative data

• Dot represents an individual or object

• Analyze the pattern of the dot distribution to determine trends

Line Graphs

• Most scientific graphs are made as line graphs.

• The lines on scientific graphs are usually drawn either straight or curved. These "smoothed" lines do not have to touch all the data points. They are called lines of best fit.

• Do not drawn in connect-the-dot fashion.

Directly Proportional and Inversely

Proportional Graphs

As the independent variable

increases, the dependent

variable increases as well.

Directly Proportional

As the independent variable

increases, the dependent

variable decreases.

Inversely Proportional

How to Construct a Line Graph

1. Identify the variables

a. Independent variable -Goes on the X – axis (horizontal)

-Dependent variable - Goes on the Y – axis (vertical)

2. Determine the scale of the Graph

a. Determine a scale that best fits the range of each variable

a. Range – the difference between your max data point –min data point

How to Construct a Line

Graph3. Number and Label Each Axis

4. Plot the Data Points

5. Draw the Graph

a. draw a curve or line that best fits the data points.

b. Most graphs of experimental data are not drawn as

“connect the dots”.

6. Title the Graph

a. Your title should clearly tell what the graph is about.

b. If your graph has more than one set of data, provide a

key to identify the different lines.

Components of a Line GraphIMPORTANT COMPONENTS OF A GRAPH

1. Title: Tells the viewer what the graph is about.

2. X-Axis

- Independent variable

- Evenly spaced units

3. Y-Axis

- Dependent variable

- Evenly spaced units

4. Key: If there is more than one line on the graph, a key is needed.

Predicting Data on a Graph

• Graphs are a useful tool in science. The visual characteristics

of a graph make trends in data easy to see.

• One of the most valuable uses for graphs is to "predict" data

that is not measured on the graph.

– Extrapolate: extending the graph, along the same slope, above or below

measured data.

– Interpolate: predicting data between two measured points on the graph.

Graphing Practice Problem #1aTime (seconds) Distance (meters)

0 0

1 2

2 8

3 18

4 32

5 50

6 72

7 98

8 128

9 162

10 200

A. Graph the data.

B. What does the graph represent?

Graphing Practice Problem #1b

A. What type of motion

does this graph

represent?

B. Put the data from this

graph into a table.

Graphing Practice Problem #1c

A. Describe what

happens during the

time represented by

this graph.

B. Put the data from this

graph into a table.