From: Walter.Hellman@f32.n105.z1.fidonet.org (Walter Hellman)
Newsgroups: k12.ed.science
Subject: Bridge Contest
Date: Sun, 24 Jan 93 22:17:00 PDT
Organization: FidoNet node 1:105/32 - On-Line Mutual Fund, Portland OR

NOTE: These Bridge Contest Rules have worked very well at our high school. 
Others are welcome to use them.

                            18TH ANNUAL MODEL BRIDGE CONTEST

                       HILLSBORO UNION HIGH SCHOOL DISTRICT 3T

Contact: Dr. Walter Hellman, Hillsboro H.S., 3285 SE Rood Bridge Rd., Hillsboro, OR 
97123   (503) 648-8561

SPONSORS: Physics departments of Hilhi and Glencoe High
A. Dates:
     Preliminaries: Hilhi and Glencoe....Feb. 8-9, 1993
     Finals:        Hilhi................Feb. 10, 1993 (7:00 P.M)
            NOTE: Adults can go directly to finals
B. Rules:
     1. Bridges may be entered in the student division by students in the 
        Hillsboro School District and the adult division by those over 18 in 
        the Hillsboro School District who are not students in the district.
     2. Bridges entered shall be constructed only of balsa wood and glue.  Cement 
        in large quantities at the joints or to coat structural members is not 
        permitted. Laminated layers of wood are permissible.     
     3. Completed bridges must have a mass of 45.0 grams or less.
     4. Bridges can be entered by individual students or a partnership of not more 
        than two people.  Only one bridge can be entered per person.
     5. Bridges should be designed to span thirty eight (38) centimeters (cm).
     6. The  outside width of the bridge shall not be more than 6.0 cm and not less 
        than 5.0 cm along the entire length of the roadway.  The length of the bridge 
        shall not exceed 43.0 cm. A 2.0 cm wide x 2.0 cm high rod must be 
        able to pass through the full length of the bridge roadway surface.
     7. The bridge may not extend more and 12.0 cm above the test support surface and 
        not more than 3.0 cm below it.
     8. The load will be applied to the bridge at the roadway surface.  The roadway 
        surface may not be more than 2.0 cm above the test support surface.
     9. When  placed  on the test stand the bridge must be able to slide  back  and 
        forth freely. Bridges cannot be wedged into the supports.
     10.All disputes will be adjudicated by the rules committee.  Their decision will 
        be final.
     11.Student bridges will tested in preliminary judging and must hold 90 POUNDS to 
        qualify for the finals.  Preliminary testing is not required for adult 
        bridges.
     12.The WINNING BRIDGE shall be declared on the basis of maximum load 
        held in each category.
     13.A SPECIAL AWARD will be given to the lightest bridge to hold 120 
        pounds.
       
C. TESTING
     1. The bridge shall be placed upon a testing stand which will consist of 
     two flat surfaces that are level with respect to each other and are separated by 
     38.0 cm.
     2. A testing block 1.9 cm wide and 1.8 cm high will be inserted across the 
     roadway through the sides of the bridge at the bridge's center.  A 1.25 cm 
     diameter steel rod will be inserted into the test block through the top of the 
     bridge.  The bridge must be designed to allow the insertion of the test block 
     and rod.
     3.  It is the responsibility of each bridge builder to examine the testing         
     equipment (which will be on display at your school) to make sure your bridge 
     conforms to the rules and can be tested.
                                      (OVER)







D. COMMENTS
     1.  The bridge does not have to look like a "normal" bridge as long as the rules 
         are met.
     2.  Any kind of glue may be used.  Balsa wood is available at most hobby and toy 
         stores.  Hillsboro Hobbies on Main St. should have a good supply.  Another 
         good source is Tammy's Hobbies on Cedar Hills Blvd. BEWARE OF BASS WOOD, 
         which is often sold with balsa wood, but which is much harder and ILLEGAL in 
         this contest.  Check with the sales person if you are not sure.
     3.  Be aware that all balsa wood is not created alike.   Density and grain are an 
         important  factors in wood strength.   Scales will be made available at the 
         schools for you to check your bridge mass. Balsa wood ranges in density from 
         about 0.1g/cm3 to 0.25 g/cm3.  A standard U.S. nickel has a mass of 5.0 g.  
         You can get an approximate mass of your wood by using a "soda straw 
         balance."  Put a pin through the center of a soda straw so that the straw 
         balances. Collect your wood in a rubber band or tie it together.
         Hang it on one end of a soda straw. Hang a plastic baggie to hold nickels on 
         the other side of the straw. Using the figure of 5.0 grams per nickel your 
         wood or bridge should not weigh more than 9 nickels. 
     4.  If you qualify for the finals you can repair and/or improve your bridge.
     5.  DO NOT MAKE YOUR BRIDGE 38.0 CM LONG.  IT MUST BE LONG ENOUGH TO EXTEND OVER 
         THE SUPPORTS WHICH ARE 38.0 CM APART! A good length to build is 40 cm.


























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