Physics and Astronomy


London Bridge



To build the strongest bridge out of Popsicle Sticks having a maximum mass of 320 grams.

The London Bridge contest will be a head-to-head competition, pitting bridge against bridge essentially in a tug-of-war along the lines of a "Junkyard Wars" contest. The winning bridge does not get destroyed, but of course, all others do.
Note: All bridges must be built before you come to the Olympics. There is no time to build your bridges on site.

PurposeTo experience a bit of Civil Engineering and construction using wood and glue. Hot glue is a poor choice.
ParticipantsTeams of up to six. Schools may enter as many teams as they wish.
Materials Popsicle Sticks having a maximum mass of 320 grams. Any kind of glue can be used but hot glue is a poor choice. No other materials may be used at all, including paper, tape, string, etc.  Please do not even use a piece of tape to write an identifier on the bridge.
  1. Rules and Regulations

    1. Preliminaries
      1. Span

        The total length of the bridge should be between 79 cm and 84 cm. It may not mount properly into the Bridge Tensioning Apparatus if it is outside of this range. The gap being traversed is 72 cm. You may make an appointment to view the Bridge Tensioning Apparatus at John Paul II Catholic Secondary School by contacting the Chief Judge (so_london_bridge@ldstf.ca). Once the bridge is set up in the device and a suitable amount of force is applied, no human intervention (such as holding the bridge in position) is allowed.

      2. Mass

        The bridge must be constructed out of popsicle sticks; you may also use toothpicks. The mass must not exceed 320 g.

      3. Road Bed

        Since the bridge is a scale model of a real bridge, scale cars and trucks must be able to drive across it. We will roll a toy "Matchbox™" car down your bridge's deck by raising one end of the bridge up 10 cm. The toy car should be able to roll from one end to the other. Toppling over, bouncing off, or getting stuck along the way warrants failure. Repeat the test four times; you must pass all four.

      4. Volume Drivability

        Since cars and trucks come in various widths and heights, your bridge must allow tall vehicles to pass along it. Your bridge should have vertical space to allow a 7cm x 7cm x 7cm cube to slide along the entire surface.

      5. Appearance

        It might just happen that the 2 final bridges collapse simultaneously. Therefore, judges in the preliminary round will rank-order (i.e., first, second, third …) bridges based on appearance.

      6. Completion

        Bridges must successfully complete all preliminaries to be eligible for the tug-of-war.

    2. Other
      1. A school may submit as many bridges as they wish.
      2. Registration deadline is 9:30 am on the day of the competition.
      3. The Popsicle™ sticks or wood must be fastened together either by gluing or by mechanical interlock. No other methods may be used. No metal pinning but wooden (toothpicks) pins are okay.
      4. The support upon which the truss or bridge will sit will be an orthogonal solid of unknown material. In other words, you'll get to rest your bridge on top of something cube-ish shaped, but maybe it'll steel, maybe oak -- who knows? (but likely not styrofoam!!)
      5. NO FAIR using last year's winning bridge!! This sneaky technique is now known as "Scafing." Use last year's design if you want, but not last year's bridge.
      6. Ties will be resolved at the Judge's discretion based on mass (i.e., the lighter bridge wins).
      7. Any truss or support material under the deck of the bridge should not be more than 5 cm below. In other words, pretend that the river's water flowing under your bridge can rise to a point 5 cm from the deck of your bridge, and that your bridge must remain dry.
      8. Your bridge must adhere to the dimensions and mass given above. Bridges that do not do so will be disqualified.
  • Tug-of-war
    1. Loading

      Bridges will be pulled toward each other by increasing the tension on a rope connecting the two bridges. A cube with a stirrup attached to it will be placed in the middle of the bridge and the rope attached to the stirrup (See Figure 1 for a close-up of the stirrup).

    2. Positioning

      To ensure the bridge is oriented according the builders' wishes, builders may hold their bridges steady when tension is first started. However, upon the judges decision, builders will have to step back and leave their bridges alone.

    3. Byes
      1. When an odd number of competitors exists in any round, (e.g., 5, 7, 11) the lowest mass bridge receives a bye for that round. This allows a remaining even-numbered amount of competitors to compete in the tug-of-war.
      2. Competitors will be randomly paired, with round re-seeded each time.
      3. Byes, when needed, are granted to lowest-mass bridges.
      4. Byes last one round. In other words, your bridge can't "sit out" for two rounds in a row.
      5. Ties are first resolved by lowest mass, then if needed resolved by the appearance, as judged by the Chief Judge.

    4. Deformation
      1. If your bridge deforms under stress more than 5 cm to the left, right, or downward, the judge may choose to disqualify it -- even though the bridge hasn't completely broken.


    Here is an example for a 9-bridge competition (which is the messiest of all possibilities). The first round would pit 4 battles of 2 and 1 bye (e.g., AxB, CxD, ExF, GxH once bridge "I" is found to have the lowest mass. In the next round there will be 5 competitors (winner AB, CD, EF, GH plus the first round bye "I." Since we still have an odd number, we need to grant another bye. Since the bye can't go again to "I", it'll go to the lightest of the recent winners. The remaining 4 competitors are re-seeded. Two winners will emerge, which added to the bye bridge leave three competitors. The bye bridge can't sit out again, so another bye is granted, this time to the least massive winner of the recent battle. This leaves two bridges in the final.

Source Jon McGoey and Perry Caskanette, London District Science Olympics.

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