A. Materials
1. You must use ONLY toothpicks and glue. NO EXCEPTIONS!
2. These must be normal toothpicks, not long craft sticks, etc. Try NOT to use the flat, thin toothpicks as they are flimsy and NOT strong enough to build good bridges. (Cracker Barrel has great ones.)
3. There is no maximum number of toothpicks you may use. However, remember that the object is to make the bridge as STRONG And LIGHT as possible (that is efficiency). Don't put in any toothpicks unless they make the bridge stronger and able to hold more weight.
4. You may use ANY kind of glue, but I highly recommend wood glue (or carpenter's glue). You can find it at any Wal Mart, Hardware store, usually even at drug stores and grocery stores.
a) Wood glue does take a long time to dry, so you may want to supplement it with hot glue (from a hot glue gun) when you need parts of it to dry fast. This works great to keep the whole project from being too frustrating. If you use ONLY hot glue, the bridge will be very flexible (which could be okay, depending on your design).
b) Some people have used model airplane or model car glue as well, but it is pretty expensive.
c) Superglue can even be okay, but it is quite dense and will be heavy if you use much, so go easy if you use it.
5. I highly advise that you sit the whole thing on wax paper, so it will be easier to unstick it if some of your glue drips. Please do not ruin your dining room table or your nice carpet with this project. ;-)
B. Design--Bridge Dimensions
1. You must have a preliminary design drawn within one week, including dimensions. I will check your design in class.
2. You do not have to STICK to that exact design, as you may choose to adapt it as you go along.
3. The MINIMUM LENGTH IS 50 CM. You will be counted off if you do not meet this minimum. I highly advise you not to go too much over that length, as it will just add weight and NOT strength. Try to make your bridge 50 cm long. MEASURE as you go with a METRIC ruler.
4. The tables will be apart 30 cm!
5. The MINIMUM WIDTH is 5 CM. (This is about the same as the length of one toothpick.)
6. There is NO HEIGHT OR DEPTH RESTRICTION. Make it as high as you need to in order to maximize the strength.
7. There MUST be a place for the BLOCK (2 x 3 x 5 cm) to sit on your bridge! You MAY have your OWN block if you like.
C. Other Design Rules:
1. You may NOT glue two toothpicks right together longways. There MUST be substantial light that can be seen between ANY and ALL of your toothpicks. You must have every two toothpicks separated by space or by another toothpick going another direction (like stacking logs in a log cabin). May overlap 1 cm!
2. You DO NEED to have crosses, as triangles are the strongest static (not moving) shape. However, the ANGLES between your crosses should be at least 45 degrees. In other words, you cannot use such small angles that you might as well have glued your toothpicks together longways.
3. You must have a ROADBED, or a flat plane on your bridge which a car could cross if it were used as a real bridge. In other words, you cannot just clump a bunch of toothpicks together in a glob. ;-) I should be able to get a toy car from one table to the other table using your bridge as a...well...bridge. ;-/
D. Grade
1. This is a 150 point grade. It is broken into two 50 point grades, a 20 point grade for using Westpoint Bridge Designer (and turning in printout of plan), a 20 point grade for your analysis sheet after the competition, and a 10 point participation grade for being involved and helping with the bridge competition.
2. The first 50 points is based on:
a) Did you turn it in on time (or early!)? Your grade will drop 10 points for EACH day the bridge is late, REGARDLESS of the reason. You have SEVERAL WEEKS to get this bridge in, and you may turn it in early, anytime you like. They are DUE NO LATER THAN WEDNESDAY, MARCH 21, 2001. THIS IS THE WEDNESDAY BEFORE SPRING BREAK.
b) Did you follow all the rules? Points will be taken off for any rule not adhered to.
c) How much time and effort did you put into the bridge? This is subjective, and depends on my opinion of your bridge.
3. The other 50 point grade is based solely on EFFICIENCY.
a) EFFICIENCY = LOAD HELD / BRIDGE MASS
b) This means you add up everything the bridge holds--the block, hook, bucket, and weights. That is the LOAD it holds. Then you divide that by the MASS of your bridge alone. This is your efficiency score.
c) Your bridge's efficiency will be RANKED with the rest of the bridges in your class. The most efficient bridge gets 50/50. The least efficient bridge ususally gets 25/50 to 30/50, depending on the class. It is possible for everybody to make A's & B's on this project.
4. You will be receiving an ADDITIONAL 10 point participation grade for this.
You must PARTICIPATE in the bridge activity, helping measure, count, clean up, write on the board, whatever needs doing. You must also test your own bridge, and help out while others are testing their bridges.
5. The other 30 points is for:
a) Using West Point Bridge Designer, and turning in a printout with your bridge plan BEFORE you build it. The deadline will be about 3 weeks before the bridge is due. (15 points)
b) You must also turn in a form with all your bridge dimensions, as well as your bridge's mass, efficiency, etc. You must also sketch your bridge on this form. You must analyze your bridge and tell me all the PHYSICS that went into the planning and testing of your bridge: FORCE, TENSION, NET FORCE, INERTIA, GRAVITY, WEIGHT, MASS, PRESSURE, etc., etc. I WILL GIVE YOU THIS FORM. You must include what you would do differently if you built a structure like this again. This is due at the END of the whole activity. (15 points)
GOOD LUCK, AND HAVE FUN DOING THIS!!!! Although each person must do their OWN bridge, it will probably be more fun if two or three people build their bridges TOGETHER in somebody's carport, etc.