Constructing Graphs

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# Constructing Graphs - PowerPoint PPT Presentation

Constructing Graphs. Why are Graphs Useful?. A graph is a “picture” of your data. Graphs can reveal patterns or trends that data tables cannot. The 3 types of graphs scientists commonly use are bar graphs, circle graphs, and line graphs. Bar Graph.

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## Constructing Graphs

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### Constructing Graphs

Why are Graphs Useful?
• A graph is a “picture” of your data.
• Graphs can reveal patterns or trends that data tables cannot.
• The 3 types of graphs scientists commonly use are bar graphs, circle graphs, and line graphs.
Bar Graph
• Used to show amounts or categories of items.
Circle or Pie Graphs
• Used to show a break down of the “pieces” that make up the “whole” of the subject graphed.

Company Expenses

U.S. Energy Consumption

Line Graphs
• Used to display data showing how one variable (Responding) changes in response to another variable (Manipulated).
• The voltage

increases as the

current increases

Voltage

Current

Global Average

Temperature

Atmospheric Carbon Dioxide Levels

Temperature o C

CO2 PPM

Year

Year

Data Tables to Line Graphs
• To plot a line graph

1. Draw the Axes
• The horizontal axis (X-axis) runs left to right.
• The vertical axis (Y-axis) runs up and down.
• Leave room for axis labels
2. Label the Axes

How do you know which variable

goes on each axis?

• The manipulated variable goes on the X- axis
• The responding variable goes on the Y-axis

Responding Variable

Manipulated Variable

3. Create a Scale
• Determine the range of the values for each axis.
• The range usually goes from zero to the highest value of the variable.
• A pattern of numbers must be established for each axis. Each grid line must be evenly spaced.
• Look for patterns in the data like 2’s, 5’s 10’s, 100’s, etc.
• The scale will depend on how much space you have to graph
• Both scales should begin at zero when possible.
Setting up the Graph Steps 1–3

Number each axis…

Must be evenly spaced…

5 10 15 20 25 30

Write RV on Y

2 4 6 8 10 12 14

Write MV on X

4. Plot the Points
• Plot a point for each piece of data (ordered pairs).
• Use the grid lines to locate where each pair will intersect.
• Start with the first pair of values and continue to the last.
• Look at the plotted points to identify a general pattern in the data.
• Connect each point with a ruler.
• Sometimes you will be asked to draw a line that comes close to all the points. This is called the “line of best fit”
• The best fit line by be straight or curved.
• Straight line (Linear graph) – use a ruler to connect points with one straight line.
• Curved line (nonlinear graph) – sketch slowly through general direction of points.
6. Title the Graph
• Add a title that identifies the variables or relationship in the graph.
• Use the subtitles on the X and Y axes to form the main title.
• If a graph has more than one line it needs a key.
Setting up the Graph Steps 4–6

Distance vs. Time

5 10 15 20 25 30

Distance (m)

2 4 6 8 10 12 14

Time (min)

Calculating Slope
• The slope of a graph line tells you how much “Y” changes for every change in “X”.
• Slope formula = “rise over run”

Y2 – Y1

X2 – X1

Interpreting Graphs

1. What is the line graph about?

2. What is the responding variable?

3. What is the busiest time of day at the store?

• 2. The number of people
• 3. 1 pm

5. How many people are in the store when it opens?

• 4. After 2pm
• 5. 2 people
• 6. About how many people are in the store at 2:30 pm?
• 6. 10 people

7. What time had the greatest number of people in the store?

• 8. What time had the least number of people in the store?
• 7. 1 pm
• 8. 10 am

Graph Animation http://www.physicsclassroom.com/mmedia/kinema/fs.cfm