In this concise video, the Engineer Guy, aka Bill Hammack of the University of Illinois, leads us through the seven design constraints that have shaped the modern cell phone. Lurking inside this lesson, though, is a more general explanation of the ways that engineers think. Here are Hammack's seven constraints:

  1. Compactness versus usability
  2. Consumer preferences
  3. Availability of energy
  4. Economic resources/availability of infrastructure
  5. Knowledge of materials
  6. Societal needs
  7. Cultural constraints

There are two really interesting nuggets in the video. First, cell phones have shrunk not just because of better battery and chip technology, but also because cell phone networks are more powerful now. That allows each individual phone to do less work receiving signals and computing. Second, plastics enable smaller cell phones. He notes that the cases of phones with removable batteries can usually be "snapped" into and out of place. The snap is a property of the plastic and knowing its precise reactions allows engineers to remove a bulky real clasp (like the kind on a lunch pail, say).

In short, I'm a sucker for a good explainer, and this one fits the bill.