ERAST Pathfinder:

Pathfinder: Measuring Wind Speed


Author: Robin A. Ward, California Polytechnic State University-San Luis Obispo


Audience: grades 5-8


Mathematical Topics: measurement, geometric construction, graph interpretation, computing averages


Rationale: The NCTM Standards recommend that the mathematics curriculum for students in grades 5-8 include explorations of real-world statistical data, which would provide students with the opportunity to:

  • systematically collect, organize, and describe data;
  • construct, read, and interpret tables, charts, and graphs; and
  • draw inferences and develop convincing arguments that are based on data analysis.

    • The Standards also advocate that students engage in concrete experiences in which they can estimate, make, and use measurements to describe and compare phenomena.

    In this activity, students will create their own anemometer, an instrument used to measure wind speed. Using this tool and the Beaufort Scale, students will measure and record estimated and average wind speeds. As an extension, students can plot and then analyze real-world wind speed data collected by Pathfinder during one of its recent missions.


    Background: Before the Pathfinder aircraft may make its flight into the earth's atmosphere, certain preparations to the plane and for the team must be taken into consideration to assure the safe take-off, flight, and landing of the plane.

    One of the most important weather conditions that must be checked is wind speed. Because Pathfinder weighs approximately 530 pounds, for a flight to be stable, winds can not exceed 5 knots. As Pathfinder reaches higher altitudes, the surface winds must range between 5 - 7 knots (approximately 6 - 8 miles per hour), with upper level winds less than 50 knots (approximately 75.5 miles per hour). Thus, a constant observation of wind speed is imperative to insure a safe return of Pathfinder to Earth.

    A knot is a unit of measurement used to measure speed at sea. One knot equals 1 nautical mile per hour or 1.151 statute (or "land") miles per hour.

    An instrument used to measure wind speed is called an anemometer. One is shown below.

    What causes the wind to blow? Click here to find out!

    In 1805, Sir Francis Beaufort, a British Admiral, devised an observational scale for measuring winds at sea. The scale is aptly named, "Beaufort's Scale". This scale classifies wind speed on a Force scale from 0 (calm) to 12 (hurricane), using observations of the winds' effects on trees and other objects.

    Beaufort's scale is still in use today by many weather stations and has been adapted for use on land. Shown below is a graphic of what you might see given various Beaufort Scale ratings.

    A wind that receives a Beaufort Scale reading above 1 would preclude the launch of Pathfinder.


    The Activity:

  • Students are challenged to build their own anemometer.

  • Next, students will go outside and measure and record the wind speed using their anemometers. To measure wind speed, students working in groups of threes will count the number of times their anemometer spins in 1 minute. (Ten turns equals 1 mile per hour.) Two of the students in the group can count the spins (for accuracy), while the other student can be the recorder.

  • Repeat the test four more times, carefully measuring and recording the wind speed each time.

  • After a total of five trials, students will associate the recorded wind speeds with their corresponding Beaufort Scale rating.

  • Using their data, students will find the average wind speed for their five trials. Students can then compare and discuss how well their measurements matched the average speed. Students can also compare their group's computed average wind speed to that of other groups. Promote a classroom discussion on the accuracy (and possible discrepancies) of their measurements.



    • Enrichment: Students can sharpen their graphing construction and interpretation abilities by analyzing wind speed data collected by Pathfinder during its August, 1997 flight.


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    • Funded by the NASA Dryden Flight Research Center


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