Lesson 8

Fill It Up

Est. Class Sessions: 3

Developing the Lesson

Part 3. Collecting and Recording the Data

Collect Data. Direct students' attention to Question 2 in the Collect section of the Fill It Up Lab pages. They are now ready to collect data and record it in a data table. See Figure 3.

Ask:

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  • Why are there columns for Trial 1, Trial , and Trial 3 on the data table? (We need to measure a container's volume three times.)
  • What if one of your measurements is completely unreasonable, for example, its value is far off from the other values? (We can delete the incorrect value. We should have 3 trials with values that are “close enough” to one another. See Content Note.)
  • What is a median? (an average or common value)
  • How do you find the median for a data set? (List the numerical values in order from least to greatest, eliminate the least value and the greatest value, until a middle value is left. This is the median.)
  • What is the median for this sample set of data: 213 cc, 216 cc, 215 cc? (215 cc)

Explain to students that they will measure the volume of each container three times and record the results under “Trial 1,” “Trial 2,” and “Trial 3” in the data table. By measuring each volume three times, students should obtain more accurate data. Then, they can graph the median of the three readings.

Students sometimes feel that they must record all data they take. However, one reason they conduct more than one trial is to detect errors in their data. If one of their three trials shows a value very different from the others, then it should be repeated. If repeating the trial confirms that the original value is probably incorrect, then it should be deleted and the new value recorded. Assure your students that this is not “cheating.” Judging the reasonableness of results is part of proper scientific procedure.

Assign Question 2. Have students work with their groups to find the volume of the different-size containers, record the data on the data table, and find the median volumes.

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Multiple Trials. Scientists use data from multiple trials to average out the inevitable errors in an experiment. At the same time, this enables them to check for large errors in measurement. If the error is too large, scientists do additional trials.

Make a Bar Graph. Once students have completed the data table, direct their attention to Question 3 in the Graph section of the Fill It Up Lab pages in the Student Activity Book.

Ask:

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  • What kind of graph should you make to show the volumes of the different containers, a point graph or a bar graph? Think about past investigations and the graphs you used.

Discuss with students the reason a bar graph is appropriate but a point graph is not. We use a point graph when it makes sense to ask about values between data points and both variables are represented as quantities. For example, in Mass vs. Number in Unit 12, students measured the mass of 4 and 6 items and could ask about the mass of 5 or even 41/2 items. The point graph enabled us to interpolate those in-between masses. When graphing the volume of different containers, it doesn't make sense to ask about the volumes of containers “between the red and the blue container” or “between container A and container B.” Therefore, a line connecting the data points on a graph of the containers' volumes would not have meaning.

Say:

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  • Discuss how you will label the axes of your graphs with your group.
  • What values did you know before you began the investigation? Let's put those on the horizontal axis. (values of the containers)
  • What variable will you put on the vertical axis? (the responding variable, Volume)
  • What unit will you make sure to include? (cubic centimeters)
  • Discuss with your group how you will number the vertical axes so that your data will fit.

Figure 4 is a sample graph of data. Note that the axes are labeled with the variable names and units and that the lines are numbered, not the spaces. The sample graph shows the vertical axis numbered by 100s. Students may number the vertical axis differently, depending on the size of the numbers they obtain.

Distribute copies of the Centimeter Graph Paper Master. Ask students to graph the median values of their data.

Student Guide:
Student Activity Book: 548 549
Answers
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SG_Mini
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SG_Mini
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Master:
A sample completed data table
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Graph of data in Figure 3
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