From: Lawrence.Chen@f3002.n134.z1.fidonet.org (Lawrence Chen)
Newsgroups: k12.sys.channel2
Subject: Re: MathMagic Solution Format Example cont.
Date: Thu, 20 Aug 92 07:54:00 PST
Organization: FidoNet node 1:134/3002 - Lunatic Haven BBS, Medicine Hat Alta

In a message dated 17 Aug 92 23:05:13 , Carol Hooper wrote:

 CH> Subject: Continuation of solution
 CH> Some of the strategy I used to help to figure out
 CH> the problem were: I meausred the thickness of each
 CH> roof.  That helps to see how sturdy the roofs are.
 CH> I also used two books for an experiment. First, I
 CH> took a tall folder and a short book.  I set them up
 CH> in a triangle shape.  It was clear to me that the
 CH> flatter triangle was sturdier than the tall one
 CH> because there was more air in between the taller
 CH> one (roof B) than the shorter one (roof A).  The
 CH> difference was 11/16 of an inch for the shorter one
 CH> compared to 23/16 of an inch for the taller one.
 CH> (I used a ruler to measure the screen.)  The answer
 CH> I came up with was A.  I agreed on A because the
 CH> air on roof A from the top to the bottom was 11/16
 CH> of an inch and roof B was 23/16 of an inch.  I
 CH> thought that the more air, the less solid the
 CH> building.  The measurement of the sides and bottom
 CH> were : Roof A Sides = 2 inches, Roof A Bottom = 4
 CH> inches,  Roof B Sides = 40/16 of an inch, Roof B
 CH> Bottom = 4 inches.  Thank you for taking the time
 CH> to read my report.
 CH>               Carli worked on the problem for about
 CH> three days.  She tried many strategies to develop
 CH> her solution and could be found in the
 CH> encyclopedias (both on-line on commercial BBS and
 CH> at home) and she made many phone calls to adults
 CH> she thought might know something about roofs.  She
 CH> took walks around the neighborhood to get a feel
 CH> for the way *real* roofs are built (aha!  Real Life
 CH> connection taking place!)  As I stated, this was a
 CH> .Gif file and I would love to be able to eventually
 CH> include graphic problems in our available problems.
 CH> However, the first problems until that thought is
 CH> probed futher will be text type.  This is only one
 CH> of many types of problems which might be given.
 CH> They will be posted according to grade level.
 CH> Please direct any questions back to me.  Thanks,
 CH> Carol

Well, solving a roof strength in the general case can be very difficult.  What you need to decide is what types of loads would be applied to the roof and the strength of its materials, and then see if the limits are being exceeded in any member of the roof.

A typical roof is composed of many trusses.....of something like this.



|||||||||||||||||||||||||||||||||||||  This is your rain load.
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

                  |            _____________ this is the load of roofing
                | v |         /              materials and such.
              | v * v |      /        <--
            | v * | * v |   *         <--
          | v *   |   * v |           <--
        | v *     |     * v |         <--   This could be a wind load...
      | v */|\    |    /|\* v |       <--
    | v * / | \   |   / | \ * v |     <--
  | v *  /  |  \  |  /  |  \  * v |   <--
| v *   /   |   \ | /   |   \   * v | <--
v *    /    |    \|/    |    \    * v <--
*===================================*

^                                   ^
|                                   |
| These are your support loading    |
| vectors....                       |

Then there's the weight of the truss itself....etc.

If she wants to really read up on how stuff like this is worked out in the real world....pickup a good Statics Textbook as a starting point....then go onto Mechanics of materials.

Then she'll have more knowledge than I picked up in my first two years in Engineering. (my major was Computer/Electrical Engineering, but the first two years is general introductory material for all Engineering students).....


Have fun 8-)


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