|MadSci Network: Engineering|
Lauren: Engineers are sometimes called "practical scientists" because we use the tools and discoveries of science to make life better for people. As I'm sure you know, the scientific method consists of four parts: First, observation of some phenomina. Second, the development of a hypothesis. Third, testing the hypothesis by experimentation or observation. Finally, review. So how do we apply the scientific method to a bridge? Start by observing and researching bridges. There are many different types: Arch bridge Suspension Bridge Cantilever bridge continuous beam bridge Simple beam bridges Truss bridges These bridges are built out of different materials: Concrete, wood, steel or stone. Here are a couple of links: http://www.howstuffworks.com/bridge4.htm&e=42 http://www.brantacan.co.uk/truss.htm In order to apply the scientific method, we must isolate the problem. That is, concentrate on only one aspect of the question. So, instead of asking "What bridge design supports the most weight?" you have to, for example, ask, "what kind of simply-supported wooden truss bridge of a specific span can support a single concentrated load at the middle?" Instead of wondering about all the dozens of different types of bridage, you concentrate on finding out about how changing one aspect of a bridge design affects how much weight it can support. I mentioned wooden trusses because there are several different designs of truss. In the 19th century, before methods of calculating stresses in bridges had been developed, there were many companies that had patented bridge designs that they sold to railroads and local highway departments. To test these truss bridges to see what design is strongest, you would have to make a model of each, with the length, depth (or height), number of panels (diagonal pieces in the middle) all exactly the same, and built out of same sized pieces of the same material, fastened together in the same way. Then you would put more and more weight on each bridge, with the weight placed on the bridges in exactly the same way, and record how much weight each supported, and what part of the bridge broke. As for materials, balsa wood is common, but drinking straws might also be used. One bridge building site I found suggested spagetti! You don't have to experiment on truss bridges, although that is what a lot of science fair entrants do. You might try experimenting on arch bridges: What carries more weight, a series of short half-cdircle arches or a long elliptical arch? Or compare suspension bridges, one with tall towers, one with short ones. I once had a group of students at my daughter's school compare bridges made of fan-folded paper: One had a few, deep folds and one had a lot of smaller folds. We put pennies on each to see which supported more wieght. (As I recall, it was the one with lots of folds. Why don't you try it?) Finally, after you've run a few experiments, have one or more of your friends look as what you did. They should be looking for anything besides what you've deliberately changed that might affect the results you get. Painful, but necessary. The heart of the scientific method is to test a series of, bridges or whatever, with as many of the details the same as possible; then change one aspect of the design, and test again and again to see what difference that one change made.
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