Instructional Activities:

MEASURING DESIGN CHALLENGE

1. Introducing the Design Process (Powerpoint, Class Discussion)

   This introduction to a design process should be linked to the problem of the case study—How would scientists design a measurement method for the microbial population they want to study? Using the Power Point, students are asked their current definition of design (slide 2). Students are then introduced to design as a problem solving approach balancing criteria & constraints. In slide 3, students are asked to identify possible criteria & constraints facing the designers for the familiar device-the ipod. Possible criteria include: portable, small, lightweight, capable of playing digital music files, be easy to operate, etc. For constraints, students might identify that the device had to sell for a certain amount of money, be able withstand rough handling, operate without a power connection, etc. Students can also be prompted to examine the social, economic, and environmental constraints in addition to technological constraints.

   Slide 4 gives an overview of steps in a generalized design procedure. Students should be made aware that design encompasses not only generating specific devices & objects but also processes. Students will follow this procedure & document each step during this lesson on the Wind Speed Design Student Sheet or in student notebooks.

2. Measuring Wind Speed (Powerpoint, Student Group Activity)
   • Introduce Design Challenge

     Slide 5 introduces the design challenge: Measuring Wind Speed. Ideally students will go outside to take measurements. A box fan, hair dryer, or similar device could be used in class as an alternate. The teacher should provide parameters such as available materials and time, but not explicitly identify these items as constraints.

   • Identify Criteria & Constraints

     Slide 6 prompts students to identify criteria & constraints. Students should work in groups throughout the procedure, discussing and then recording each step as assigned. The problem statement should be intentionally vague so that students need to grapple with clarifying criteria & constraints. It is anticipated that students will have a much easier time identifying constraints and will possibly identify “measure wind speed” as their only criteria. This is fine, setting the stage for criteria to be re-evaluated later in the lesson.

   • Brainstorm Possible Solutions

     Once the criteria & constraints are identified, students should be given some time to brainstorm possible approaches. Depending on the students, designate an amount of time and a number of possible solutions needed. They could record these ideas on whiteboards or on poster paper. Teachers should emphasize that at this point it is more important to generate options—no ideas should be dismissed. If they struggle, groups could share ideas in progress to help prompt more possibilities. Students must have at least two options (from within their own group or from the class overall) for the next step.

   • Weigh Tradeoffs, Carry Out Plan, & Evaluate

     Slide 7 prompts them to weigh tradeoffs to choose an approach to carry out. Next, a set time for actually measuring the wind speed should be given. While student groups are collecting & processing data, prompt them to record significant figures appropriate for the level of uncertainty in each step of their approach. If not previously covered in class, these concepts should be addressed explicitly prior to students evaluating their results & suggesting improvements. Upon completion, a focus of the whole class debrief should be to have students evaluate their designs in terms of their self-identified criteria. At this stage, students may recognize that the criteria need to be more explicit to appropriately judge success. The proposed application for the measurement in the next slide will help push along the conversation if necessary.

   • Refine Criteria for Instrumentation

     Slide 8 introduces a possible application for their wind speed measurement design. The intention is to reveal that the application for a measurement drives much of the design criteria to evaluate a success. Issues such as precision, accuracy, frequency of sampling, averaged vs. instantaneous readings, etc. should be the focus of the discussion. Teacher Note: The reliability of inferences from proxy variables will be addressed in more detail in the next lesson. The final evaluation piece is for students to identify criteria suitable for track & field wind assistance measurements. Students should explicitly reference ideas addressed in the discussion—ie the design will measure wind speed with an uncertainty of ± 0.05 m/s, etc. Teacher background: More information about wind speed and track & track & field records can be found under wind assistance on wikipedia.