Shopping Bag Timeline - Phase 2
With bag classes freshly minted in their minds, students next investigate how shopping bags behave when loaded to failure. They do this in order to make better design decisions in Phase 3 -- ones based on their experiments and hands-on experience. Such tests can be done quantitatively, where students adding measured loads until the bag fails. A more qualitative approach involves students put their foot in the bags and push until the bags give way.
Getting students to focus attention on where and how bags fail can be difficult. Younger students will be tempted to do this in "karate" fashion. Since the goal is to learn something beyond the fact that the bags can be destroyed, you may want to encourage students to:
- apply forces so as to approximate a bag that is carrying a large load of groceries or books (press slowly, don't kick)
- apply force gradually so as to discover the stages through which failure occurs, and to estimate better which forces are greater