Research in Engineering Education Symposium 2011 - rees2009

Universidad Politécnica de Madrid (UPM) Página 854 de 957
have 12 foot in length, and we need cross-section. Force. Okay, strain relates to length.
Stress. Young‘s modulus relates stress and strain. So, I‘m going to try to play with the
equations see if something comes up. Here we have… so I‘m looking for stress F, ah not F. I
need the strain. I‘m going to take strain back to basic lengths. Hmm… I‘m going to go back
through the book some more see if I can find some more equations.”
Each of the open-ended problems had more than one unknown. A process that many
students used to reduce the number of unknowns was to select a value for one of the
unknowns and then solve for the other. This often involved selecting a material to fix
material property values. Sarah provides an example of how she developed such a plan.
“Okay, well. I don‘t really know where to start, but I guess it doesn‘t matter what the
platform is or how many strands because it said each one will be 12,000 Newtons and the
design requires a safety factor of 2. So, I think that means it needs to be able to support
24,000 Newtons. So an appropriate material for these strands and strand diameter. Well,
I‘m going to have to look up some materials. (Re-reading question) Um, I guess I‘ll look up
yield strength or something. Oh yeah, I can use yield strength because then that will help
me get the diameter because of force over area.”
Iteration was a tactic that some students used to deal with the ambiguity of the problems.
Brandon, for instance, adjusted the safety factor that he was using for one problem in an
attempt to narrow in on a solution. ―Maybe we don‘t have to be so safe. Maybe we can use
a safety factor of 1.5. 75.5 divided by 1.5. That‘s good. (Calculating) 500,000 divided by 50
times 10 to the 3 is 10 times 144, 1440 times 0.289, dang it! All right, even being less safe
doesn‘t help, so we need something with a (looking in book), less of a density.”
The way in which decisions were made to deal with ambiguity
Students made several kinds of problem solving decisions when confronted with
ambiguity in the problems. They made both functional decisions that allowed them to
move forward in the problem (“I‘m going to just pick one to start with and I‘m going to use
steel alloy.”) and decisions that they felt would help avoid getting stuck, even if those
decisions were not actually part of the problem statement (“…this is an outdoor project,
we need corrosion resistance.”).
Some students made arbitrary assumptions in response to the ambiguity that they
encountered. Robert explained that, ―The problem with this problem is that they don‘t
really give you a design life expectancy, so with that you have to deal with corrosion and
other things. So the design parameters are again kind of vague. So when they give you
vague you assume to make it the easiest on yourself.” And James picked a numerical value
for one of the unknowns that he thought might result in simple calculations, explaining,
“Just for the sake of getting this done I‘m going to assume that it‘s, hmm, wondering what
would be reasonable. Perhaps one square inch would be easy.”
Several students relied on a personal knowledge base or past experiences to inform the
decisions that they made. Ryan, for example, used his knowledge to help narrow down his
material choices, explaining, “Okay, so tension means that um, ceramics can‘t be used no
matter what because they‘re only good in compression.” Other participants, such as Alex,
Proceedings of Research in Engineering Education Symposium 2011
Madrid, 4 th - 7 th October 2011