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Mr. Lewis Classroom |
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 FAQFrequently Asked Questions: This page contains answers to common questions of students and parents.
What are the requirements for building the toothpick bridge? TOOTHPICK BRIDGES OBJECTIVE TO DESIGN AND BUILD A BRIDGE WHICH CAN BE TESTED FOR STRUCTURAL STRENGTH AND THEN ANALYZED FOR THE FORCES INVOLVED MATERIALS ROUND OR FLAT WOODEN TOOTHPICKS ELMER'S WHITE GLUE INSTRUCTIONS EACH STUDENT WILL RESEARCH BRIDGE DESIGNS FROM LITERATURE OR ACTUAL STRUCTURES NOTING BRACING POINTS AND REINFORCEMENTS AND HOW EACH DESIGN TAKES INTO ACCOUNT GRAVITATIONAL AND LOAD FORCES AND THE MATERIALS USED. EACH STUDENT WILL THEN DESIGN AND BUILD A BRIDGE USING WOODEN TOOTHPICKS AND ELMER'S WHITE GLUE SPECIFICATIONS THE TOTAL WEIGHT OF THE FINISHED BRIDGE CANNOT EXCEED 40 gm ANY DESIGN CAN BE USED AS LONG AS THE ROADBED IS FLAT AND UNOBSTRUCTED TO ALLOW A MATCHBOX CAR TO TRAVEL ITS LENGTH. THE BRIDGE MUST BE FREE STANDING AND ALLOW FOR A 2 cm X 30 cm BOARD TO PASS UNDER THE BRIDGE WHILE IT RESTS ON A FLAT SURFACE. ONLY THE MATERIALS LISTED MAY BE USED TO BUILD THE BRIDGE. EXCESSIVE AMOUNTS OF GLUE MAY NOT BE USED AS PART OF THE STRUCTURE, i.e. THE BRIDGE MAY NOT BE COMPLETELY COVERED WITH GLUE. PROCEDURE TO TEST EACH BRIDGE'S STRENGTH WE WILL PLACE THE BRIDGE ONTO AND BETWEEN TWO FLAT-TOPPED TABLES SPACED 25 cm APART. AN 8" WOODEN DOWEL WITH A 1/2" DIAMETER IS SET ACROSS THE MIDDLE OF THE ROADBED. TWO LOOPS OF STRONG CORD ARE ATTACHED TO THE HANDLE OF A 5 gal BUCKET. EACH LOOP OF CORD IS THEN LOOPED OVER EACH END OF THE DOWEL TO SUPPORT THE BUCKET BELOW THE BRIDGE. SAND OR WATER IS ADDED TO THE BUCKET UNTIL THE BRIDGE BREAKS. THE BUCKET AND ITS CONTENTS ARE THEN WEIGHED. RANKING EACH BRIDGE WILL BE RANKED USING A RATIO OF LOAD WEIGHT TO BRIDGE WEIGHT. What are some tips for building a toothpick bridge? Tips for Building Toothpick Bridges Goal: To make a structure using only round wooden toothpicks and glue that will: 1. Span at least 20 cm. This means that for at least that distance, there can be nothing supporting the bottom of the bridge. 2. Weigh less than 50 grams. 3. Support a weight stacked on a 9" wooden dowel placed on top of the structure. Note from the rules that the winner is judged on the capacity of the bridge - weight supported/weight of the bridge - not on the total weight supported. That means that a very light bridge that is moderately strong might win over a stronger, heavier bridge. Your bridge design should consider several things: �h Tension and compression. Some members on the bridge will be loaded in tension - the force tends to pull out on both ends - while others will experience compression - the force pushes in, trying to shorten the member. Members in compression need to be stronger. They tend to bend in the middle, or buckle. (You can probably snap a toothpick by squeezing it between your fingers, but can you pull one apart?) You can add supports to the side of a long compression member to prevent buckling. �h Abutments. Your bridge will be placed between two tables. Designs that make solid contact with the supports will not tend to spread apart as the load is applied. �h Span limitations. Designs that have a continuous bottom chord - flat boxes - must be placed on top of the supports in order to achieve the span. These bridges can't take advantage of the support offered by the abutments. Note that if your bridge has an arch shape, but flat supports at the base, the 20 cm span must be measured from the inside of the structure. �h Loading methods. The weights will be stacked on top of the bridge. Some bridges have held over 300 lbs! This ends up with a large stack of weights balanced on a tiny bridge. The rules say you can't have any lateral support to keep the bridge from tipping toward or away from you - it must stand on its own. Design you bridge with a flat, level surface on top to support the 9" dowel Plan for width. Narrow bridges with cross members made from single toothpicks are often too narrow, and tip when the stack of weights gets too large. You might try one of the following, or a combination: �h Posts. Glue several toothpicks side by side to build up round members. These will be very strong in compression, but will have to be supported to keep from buckling. �h Trusses - like the rafters in a roof, or a typical steel bridge. Trusses are usually built by connecting a series of triangles in a plane. The bridge is built by setting two trusses parallel to each other and connecting them with cross members �h Triangular space frames. Start by gluing three toothpicks into a triangle. This is your base plane. When it dries, add three more toothpicks (one at each corner) to form a 3-sided pyramid, or tetrahedron. You can add to this shape by gluing three more toothpicks to any of its triangular faces. The weakest point on these is usually the corners. Let the toothpicks cross over each other slightly, and cover the joint in glue. What are the requirements for building the catapult? CATAPULTS OBJECTIVE: CREATE AND UTILIZE A CATAPULT TO ANALYZE PROJECTILE MOTION. INSTRUCTIONS: EACH STUDENT WILL BUILD AND USE A CATAPULT TO PROPEL A LARGE EGG OVER A ONE-METER-TALL WALL. THE CATAPULT MAY BE NO CLOSER THAN ONE AND A HALF METERS FROM THE WALL. SPECIFICATIONS: EACH CATAPULT MAY HAVE A MASS NO GREATER THAN ONE KILOGRAM AND A HEIGHT NO MORE THAN ONE-HALF METER. CATAPULTS ARE RESTRICTED TO THE USE OF A LEVER-ARM DESIGN ACCELERATED FORWARD BY A RESTORING FORCE. RANKING: TO RANK STUDENTS MUST PROPEL THE EGG OVER THE WALL SAFELY. CATAPULTS WILL BE RANKED USING A RATIO OF DISTANCE IN METERS TO WEIGHT OF DEVICE IN KILOGRAMS. What are the requirements for building the roller coaster? ROLLER COASTERS OBJECTIVE TO DESIGN AND CREATE A ROLLER COASTER THAT CAN BE USED TO ANALYZE THE ENERGY EXCHANGES INVOLVED IN SUCH A SYSTEM. MATERIALS CHOICE OF MATERIALS IS AT THE DESCRETION OF THE STUDENTS. ALL MATERIALS ARE TO BE PROVIDED BY THE STUDENTS. ALL CONSTRUCTION IS TO BE DONE OUTSIDE OF THE CLASSROOM. NO PREFABRICATED PARTS MAY BE USED (i.e. HOTWHEELS TRACKS FOR WAL-MART). INSTRUCTIONS EACH STUDENT WILL RESEARCH COASTER DESIGNS FROM LITERATURE OR ACTUAL STRUCTURES NOTING BRACING POINTS AND REINFORCEMENTS AND HOW EACH DESIGN TAKES INTO ACCOUNT GRAVITATIONAL AND LOAD FORCES AND THE MATERIALS USED. EACH GROUP OF STUDENTS WILL THEN DESIGN AND BUILD A ROLLER COASTER STUDENTS WILL KEEP DAILY JOURNALS REGARDING RESEARCH, RESULTS, CHANGES, AND THE CONTRUCTION PROCESS. EACH JOURNAL WILL INCLUDE A PRELIMINARY AS WELL AS COMPLETED SKETCH OR DRAWING. SPECIFICATIONS EACH COASTER MAY NOT EXCEED ONE METER IN HEIGHT OR LENGTH. THE COASTER MUST BE FREE STANDING AND ATTACHED TO A BASE. THERE IS NO WEIGHT LIMIT FOR THE COASTER BUT IT MUST BE PORTABLE. THE TRACK MUST INCLUDE A LOOP AND A SECOND ELEVATION. ANY DESIGN CAN BE USED AS LONG AS THE ROADBED IS FLAT AND UNOBSTRUCTED TO ALLOW A MATCHBOX CAR AND GOLF BALL TO TRAVEL ITS LENGTH. PROCEDURE EACH COASTER MUST FIRST ALLOW A MATCHBOX CAR AND THEN A GOLF BALL TO TRAVERSE THE ENTIRE TRACK SAFELY A FRESH EGG WILL BE PLACED AT THE END OF EACH TRACK WHEN TESTED. THE OBJECT IS TO COMPLETE THE TRACK WITHOUT FLIPPING UPSIDE DOWN AND SLOW DOWN ENOUGH NOT TO CRACK A FRESH EGG WAITING AT THE END. RANKING EACH COASTER WILL BE RANKED USING A CHECKLIST FOR COMPLIANCE WITH THE LISTED CRITERIA. Construction: Height under 1 meter..................5 pts Length under 1 meter..................5 pts Freestanding on a base................5 pts Contains a loop......................10 pts Contains a second elevation..........10 pts Contains a banked curve..............10 pts Evaluation: Ball traverses entire track safely...10 pts Car traverses entire track safely....10 pts Ball does not break egg...............5 pts Car does not break egg................5 pts Journal: Entries must be made each day........25 pts  |
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