2020(S08) Lecture:week 9

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Week 9 Tuesday

“Faith is a poor substitute for reason” Thomas Jefferson

As you hone in on the details of your projects, your team should plan ways to validate the system's operation and ways to learn from its glitches. We have two quick challenges for you today. The first illustrates that even the "best" answers you can offer that are consistent with all available data remain tentative, that the answer is either strengthened or revised by additional data and that all interpretations are subject to personal biases, human values and the various ways we all think about the world. The second challenge puts you midstream in a flawed design and requires that you consider the modes of failure to debug/troubleshoot the problem.
We will spend only 20 minutes on these challenges and then you and your team can use the rest of today's lecture time to prepare for tomorrow's Tech Spec Review.Please plan to arrive at 2PM for tomorrow's presentations. Speaking order will be determined by the order in which your .ppts are sent to Natalie.

Challenge 1: The check's in the mail

This challenge is adapted from Judy Loundagin's lesson, here.

  1. One member of your team should serve as scribe (with notebook sheet to be provided). Another should be spokesperson (see item 7, below).
  2. Each team should get one envelope that is filled with fictional checks. Do not look at the checks yet. All envelopes have the same checks.
  3. Remove and examine 4 checks only.
  4. Discuss a plausible scenario which involves those checks.
  5. Once your group has agreed on a reasonable scenario that accounts for the checks, and the scribe has written it down, then you can draw 4 more checks from the envelope. As tempting as they are, the unchosen checks must stay in the envelope, unexamined.
  6. Reconsider your initial scenario to include the information you can glean from all 8 of the checks.
  7. We will take 1 minute to hear from each team. The spokesperson should detail
  • the content of the first 4 checks,
  • the way your team considered their content and
  • the initial conclusion you drew
  • the details of the next 4 checks and
  • the revisions you made to the scenario to accommodate the information.

Finally, the spokesperson should say what kind of check they would expect to see in the envelope if their scenario is correct OR what kind of check would blow their ideas out of the water and demand a full re-write of their explanation.

Challenge 2: Soap Stress

Compressional stress on a cube
Compressional stress on a cube
Tensional stress on a cube
Tensional stress on a cube
Shear stress on a cube
Shear stress on a cube

This challenge is adapted from one described at teachengineering.org. We will skip the preliminary descriptions of plate tectonics and just remind you of three stresses that give rise to deformation: compression, tension and shearing forces.

sample of soap packaging and damage
  1. Begin by looking at how the packaged soap is breaking during shipment from the factory to the distributor (a sample of the broken soap will be available for you to look at). Decide as a team which kind of stress could be leading to this kind of damage. Pick only one kind (i.e. not a combination of tension and shear) and rate your confidence in that choice on a scale of 1-10 (1 = we had to pick something so we picked this, 10 = I'd bet my house on it)
  2. Now start counting costs to analyze and fix what you believe to be the failure mode.
    • if you'd like to stress an unbroken soap bar, each bar costs $1
    • if you'd like to use paper to wrap each bar of soap, each sheet of paper costs $0.01
    • if you'd like to use a small piece of cardboard to line each bar of soap, each piece of cardboard costs $0.05
    • if you'd like to use larger sheets of cardboard to line each 12 pack of soap, each large sheet costs $0.50


In 5 minutes, your team will be asked

  • which of the three stresses you believe could be breaking the bars of soap
  • how confident you are with that choice
  • what you'd propose as the best way to fix the problem
  • how much you spent to arrive at that recommendation and what your proposed solution will cost
  • and finally if you are more or less confident in the source of stress that's breaking the soapbars after this quick round of failure analysis, and debugging.

Be sure to wash your hands before you touch your eyes if you've been breaking soap to test it.

Mapping these challenges to your project

There is no such thing as either complete knowledge or flawless design. And if you believe, as Henry Petroski does, that "...the central goal of engineering is still to obviate failure, and thus it is critical to identify exactly how a structure may fail." (pg 195 in To Engineer is Human), then you and your team will dedicate effort

  • to collecting relevant data that validates or disproves the ideas in your own project and
  • to anticipating failure modes so debugging your design is trivial rather than backbreaking.
    If these ideas of validation and debugging can be included in your Tech Spec Review for tomorrow, then great. If not, then be sure to include them in your final design at the end of the term.

Week 9 Studio

Technical Specification Review

Week 9 Thursday

Project Re-design

Based on the work you've done so far, the questions you heard yesterday after your presentation and the short amount of feedback you'll get today, it's time to prioritize what work still needs to get done on your project. Over the next few weeks, we will continue to offer tools for implementing different natural and engineered solutions, and we will try to provide consultants working in these fields to help you see your project through their more experienced eyes. You should leave today's class with a clear sense of what the work flow for the next few weeks will be.
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