Goals
To develop students' awareness of the importance of standardized measurements and the need to calibrate their instruments to established standards.
Objectives
1. Students will be able to identify likely causes of measurement errors.
2. Students will understand the concept of calibration against known standards.
Time
One class period (45-50 minutes)
Materials
1. Set of intentionally faulty rulers
Introduction
One of the most profound scientific accomplishments of modern civilization is the establishment of international standards and units. Discuss with your students whether international commerce and science would be possible without established standards. Discuss how we can be sure that the hundred meter dash is precisely the same length everywhere. How can we know that the seconds used to time the dash are the same duration in Moscow as they are in Boston? Engage your students in discussion about how measuring devices in all seven continents are calibrated against the same standards. What is the purpose of each country's bureau of standards? Why is there international cooperation around world standards?
Scientists everywhere labor to ensure the accuracy of their instruments and the compatibility of their measurements. Like professional science, all collaborating schools must share these same concerns. They must use standardized units of measurement and calibrate their instruments according to common scientific procedures. To make your students aware of these needs, we propose a set of simple exercises with stopwatches and intentionally faulty rulers.
Management
This activity is divided into two sections. The first is the stopwatch exercise, which should last approximately five minutes. The second is the ruler exercise, which should last approximately twenty minutes. .
For this activity, organize your class into teams.
Each team should assign one member to serve as the team's Communicator.
Procedures
Stopwatch Exercise
The purpose of this exercise is to engage your students in making a simultaneous measurement. They will measure the duration of time (in seconds) it takes a student to count off fifteen seconds.
Organize your class into the teams and select one student to count aloud "One thousand, two thousand, three thousand,...." up to fifteen. Each team should use at least one stopwatch to measure in seconds the duration of the count (use wristwatches with second hands or digital watches if stopwatches are unavailable). The student should signal the beginning and end of the count by raising and lowering his/her arms. The Communicators should record each team's result and the class should discuss the reasons for any deviations.
Ruler Exercise
Distribute one poster, Standards & Units, and a sheet of one kind of ruler (A, B, C, D, or E) to each of the five teams. Each team should measure with their rulers the height, width, and area of the poster and write down their results, including the units. Have the teams repeat the measurements until they arrive at a reasonably consistent set of measurements.
Discuss the results. Are they close to one another in value? If yes, what kinds of calculations did each team have to do in order to reach its answer? If not, how could errors have occurred? Students should consider possible errors due to their procedures and to the rulers. How were their rulers flawed and how could they be corrected?
After your students have finished measuring, distribute copies of Understanding the Ruler Exercise and discuss the standardization of instruments. Arrive at a consensus as to the area of the poster.
Telecommunication
Students can telecommunicate to their collaborators both the results of their ruler exercise in square centimeters and the deviation of their probes.
Assessment
Propose different kinds of instruments or rulers and ask students to devise a calibrating strategy to determine their accuracy.
Challenging Extensions (Optional)
Students can determine the accuracy of a measuring device by asking the manufacturer how the instrument was calibrated. They should try to trace the calibration of the tool all the way to the world standard. They can talk to a local pharmacist, jeweler, or gas station about the degrees of accuracy they require of the measurements they make. How often are their instruments calibrated and what is the procedure?
Connecting Disciplines (Optional)
1. History Ask students to write an essay about the history of measuring units, their evolution, and their convergence to world standards.
2. Physics What are the world standards for time, distance, and mass, and how are they determined so that everyone can compare data? What is the modern world standard for measuring time? Read about the development of the atomic clock.
3. Social Studies What barriers did America encounter when it tried to shift to the metric system?
4. Biology What are circadian rhythms? What is a biological clock?
References
Assault on the Unknown: The International Geophysical Year, Walter Sullivan, McGraw-Hill, New York, 1961, ed., 1990, pp 785 ff.
"Measures and Measuring Systems," Encyclopedia Americana, 1993, pp 584 ff.
The Modernized Metric System, (U.S.) National Bureau of Standards Special Publication 304A.
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