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 Vo

ltage

Current

CO2

PPM

Year

Year

Tem

pera

ture

o C

Global AverageTemperature Atmospheric

Carbon Dioxide Levels

Data Tables to Line Graphs

To plot a line graph follow these steps…

October TemperaturesDay Temperatur

e o F1 432 533 504 575 596 67

October TemperaturesT

emperature o F Day

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

Manipulated Variable

Resp

ondi

ng

Varia

ble

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.o Look for patterns in the data like 2’s, 5’s

10’s, 100’s, etc.oThe scale will depend on how much space

you have to graphoBoth scales should begin at zero when

possible.

Setting up the Graph Steps 1–3

Write MV on X

Writ

e RV

on

Y

Number each axis…Must be evenly

spaced…

2 4 6 8 10 12 14

5 1

0 1

5 2

0 2

5 30

Time

(sec)

Distance (m)

2 54 106 158 2010 2512 30

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.

5. Connect the Points with a Line

or 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.o Straight line (Linear graph) – use a ruler

to connect points with one straight line.o Curved line (nonlinear graph) – sketch

slowly through general direction of points.

Connecting the Points

Best Fit Lines

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

2 4 6 8 10 12 14

5 1

0 1

5 2

0 2

5 30

Time (min)

Dist

ance

(m)

Time

(sec)

Distance (m)

2 54 106 158 2010 2512 30

Distance vs. Time

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?

1. The number of people in a store during different hours of the day2. The number of people

3. 1 pm

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

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

6. About how many people are in the store at 2:30 pm?

4. After 2pm

5. 2 people

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