Project: Designing a Virtual Bridge

There are an abundance of simple, yet though-provoking problems involving Newton's Laws. Two of my favorites:

  • If the earth is pulling me down with gravitational force, what is providing the equal and opposite force stipulated by Newton's Third Law? (Hint: it is not the ground pushing up on me, since the earth is pulling on me whether I am touching the ground or not).
  • When a car accelerates, what is the providing the external force that accelerates the car? (Hint: it is not the engine, or the tires, both of which are part of the car)

Note that both of these problems require qualitative answers. Although physics is often associated closely with mathematics, the student should also be able to understand its basic laws without drumming out a quantitative example.
Indeed, once a student has mastered the ideas and the mathematics, it becomes clear that the number of forces involved in a real problem can be large, and we haven't developed all the tools we need to solve the mathematical piece of the problems. Yet, we want to be able to look at a realistic problem.
The West Point Bridge Designer provides a nice way to look at a complicated structure and understand the forces in both a qualitative and quantitative way, and we have a project based on the program.

  1. Start with the online tutorial.
  2. Create a blog post titled "West Point Bridge Design." Create a Projects category, and add the category to your post. Add the projects category to your main menu, so that I can find your projects from your site menu.
  3. Paste the bridge project template into your webpage, and fill it in.

A few observations/thoughts that you might want to work into your project report:

  1. You can take screenshots on the Mac by pressing Shift-Command-4.
  2. When you use the Add Media button in WordPress for a screenshot, it can make the image appear small. To make your screenshots appear bigger in your blog, change the img src to match the URL in the anchor tag that wraps the img tag. If that sounds like Greek to you, ask Mr. Benson for help.
  3. In the bridge, members are red if in compression (risk of buckling), and blue if in tension (risk of being pulled in two)
  4. Compressive forces push on a joint, and should be portrayed in your free-body diagram as pulling from the opposite side of the dot representing the joint.
  5. Make sure you include a screenshot of the joint for which you are sketching a FBD.
  6. Joe used Google drawing tools for the FBD, which worked well.
  7. In the conclusion paragraph describing what you have learned from this project, think of bridge improvement ideas that you discovered as you refined your design. For example, what can you do to increase the tensile strength of a member? What else can you do to increase compressive strength? What adjustments to the bridge design did you find most effective in reducing the cost of the bridge? Do tubular members improve tensile strength? How about compressive strength?

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