The story of that demonstration of the concept of the bridge is really interesting. Before the days of electronics to be able to get such a concept across was a difficult proposition. The solution is very good and filled the bill well.
I have been on that bridge, by the way. It is a great view.
This is definitely a great way to illustrate concepts of stress and strain! I'll have to keep this technique in mind when trying to explain mechanical problems. By the way, here is a picture (from Wikipedia):
What I really like about the human model described here is that the humans could feel the tensile and compressive forces, rather than just imagine them. Seems like it would be a great exercise for engineering students.
Using words to let us paint our own mental picture is to me the essence of teaching. Teach us to read and imagine, then present a problem and describe a solution and let our minds create the picture and fill in the details. I read the article and had a pretty good concept of what was being described, when I saw the photo, it was obvious what had been described and the details clicked immediately into place. I think those of us who learned to read before there was television may be luckier than our children who had all the solutions presented visually before they developed the ability to imagine. I always enjoy your articles Professor Petroski.
Ken, You are absolutely correct. A picture is worth a lot of words, but it was my understanding that my column was not to be illustrated. Thanks to Mr. Palmer for inserting the classic photo into his comment. HP
This article may not be illustrated, but "Engineers of Dreams" is, and I remember the image shown below is in that book. I've kept it on my shelf waiting for my son to be old enough to understand and appreciate it as he heads towards an engineering career.
Sorry, Mr. P, I had no idea there was any such limitation, it seems I see photo's here quite regularly. Editor?
Bob from Maine, I'm quite proud of my ability to describe things accurately, but like most engineers regardless their artistic ability, I am always sketching stuff during discussions. One wouldn't commit schematics or drawings to a written description. Imaginations are way too variable to assure our minds are on the same page.
I'd seen this fantastic photo some time ago too, (Perhaps in Mr. P's book) and although it all sounded familiar, I still didn't put it together.
An interesting title, although my experience is that designs build on designs. It is often easier to imagine an improvement of some kind when looking at a design then when looking at a blank sheet. Even an unworkable dsign can serve as a basis for ides to produce a much better design. At least that is often what I see. Of course, sometimes we can only guess about what the main goal of a design was. Some designs seek to minimize the required accuracy of components, others strive for the maximum robustness, and it is obvious that many designs are optimized for minimum initial cost, with little attention given to other variables.
So every design can serve as a basis for additional designs, optimized for some particular variable parameter.
Design does beget design. In the article, the design of the demo was a result of the design of the bridge. That is the circle of life of engineering. If you design an end item, there are many other designs that are necessary to make your assembly a reality. If the component requires plastic parts, someone has to design the molds for the part. Someone else handles the design of the molding mahcine to run the molds. This goes on up and down the chain keeping engineers in business.
The comment about secondary required designs brings out the old comment "Nothing is ever simple". The truth is that usually an over-all design does require a lot of little designs, such as nuts and bolts. The good news is thgat we don't need to design those parts new each time.
Dr. Petroski--absolutely fascinating article. I love these stories that give background and weave into the narrative personal history regarding the engineer(s) doing the work. We sometimes forget that many many great engineering designs were accomplished with slide rules, pencils and erasers. (Big erasers at that.) Really demonstrates how far we have progressed with technology. I wonder where we will be fifty years from now. Again, many thanks.
What should be the perception of a product’s real-world performance with regard to the published spec sheet? While it is easy to assume that the product will operate according to spec, what variables should be considered, and is that a designer obligation or a customer responsibility? Or both?
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