Constructing Graphs

1. Constructing Graphs

2. 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.

3. Bar Graph • Used to show amounts or categories of items.

4. 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

5. 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

6. Global Average Temperature Atmospheric Carbon Dioxide Levels Temperature o C CO2 PPM Year Year

7. Data Tables to Line Graphs • To plot a line graph follow these steps…

8. 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

9. 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

10. 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.

11. 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

12. 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.

13. 5. Connect the Points with a Lineor Draw a line of “Best Fit” • 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.

14. Connecting the Points

15. Best Fit Lines

16. 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.

17. 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)

18. 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

19. 1. The number of people in a store during different hours of the day 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

20. 4. At what time does business start to dramatically slow down? 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

21. 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

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