“SECME: 21st Century Pioneers – Dreaming Today To Discover Tomorrow” Basic Instructions For the Mousetrap Car Competition Team entry: 3 students required Design Mousetrap car construction and run Communication Technical report writing Design drawings Team interview with Judges Mousetrap Event Final Scoring Total of the following scores Mousetrap car performance (100 pts max) Design drawing (50 pts max) Technical report (50 pts max) Team interview (50 pts max) Total Max – 250 pts Design drawing Title card (4” X 6”) Team name School name and address Team members names, addresses and grade levels School coordinator’s name Date of Competition Paper size (18” X 24”), 1” margins,16” X 22” actual drawing Must show scale and units (use 1:1 and inches if possible) Label all parts Three views (front, side and rear) Dimensions Accuracy Neatness (pencil and fully erase) REAR VIEW FRONT VIEW SIDE VIEW Title: SECME Mousetrap Car Drawn by: Lavonis Dubose Date: 1/25/2003 Scale: Full 1” = 1” Technical Report Writing Describe the design, construction and operation Computer printed, 12 pt. Type, double-spaced White, 8-1/2” X 11” paper, 1” margins Maximum of 5 pages Graded on Outline Organization Precision Sentence formation Mechanics Technical Report Organization Cover page (required to contain) Title Name, addresses and grade of team members Team’s school name and address School system name School Coordinator’s name Date Abstract (1/2 page summary) Table of contents (1 page) Introduction Design Construction procedure Operation of the mousetrap car Conclusions / Recommendations Acknowledgements Appendix (sketches, tables, charts etc.) 5 page maximum Team Interview Requirements All three members present Each responds to questions Work is students’ own True team effort is evident Team Interview Evaluation Categories Teamwork Application of technical principles Knowledge of design Oral communication skills Mousetrap Race Scoring 2 Weight of Mousetrap _________________ Weight of Car Goal: Minimize weight Minimize length Maximize distance Distance _______ Length Basic Instructions For Building A Mousetrap Car This is a set of basic instructions and tips on how to get started building a mousetrap car out of balsa wood. Many other materials and designs are possible Adapt the instructions to your needs and imagination. Materials Mousetrap Chassis: wood scraps, balsa wood, ice cream sticks, stiff wire Axles: wooden dowels, metal tubes (copper or brass), axles from old toys Wheels: Metal lids, CDs, wheels from old toys, other diskshaped objects Pull Cord: String, rubber bands or fishing line Glue (strong enough to withstand force of mousetrap) Tools: Pliers, screwdrivers, hammers, handsaws and drills Use recycled materials whenever possible Physics Concepts Friction Friction is the resistance of motion between two objects. Most friction between the materials in your car reduce the amount of energy that is used to move the car, so it would make sense that you want to reduce that friction. However, you actually rely on the friction between your wheels and the floor to help your car move. Another, less thought of, friction involved in the performance of your car is air resistance. Remember, air resistance acts against the motion of the car and therefore should be reduced to increase performance. Physics Concepts Newton’s Laws Newton’s first law is also known as the law of inertia. Inertia is an object’s tendency to resist change. The more massive an object is, the larger its inertia, and therefore the harder it is to change its motion. Newton’s second law is most commonly known in its equation form, F=ma. Both of these laws should show you that the more massive your car, the more force that will be required to move the car. Remember that, depending on the goal of the car, you may want the car to have some inertia so it will keep moving after the mouse trap has used all it energy. Keep these laws in mind while constructing your car. Physics Concepts Rotational Inertia Just like linear inertia deals with an object’s tendency to resist change of its linear motion, rotational inertia is an object’s tendency to change its rotational motion. The rotational inertia of an object depends on its mass and the distribution of that mass. Since the wheels of your car are the parts that are rotating, you may want to decrease or increase their rotational inertia. Physics Concepts Energy Energy can be defined as the ability to do work. Work is the applying a force to an object, and actually moving that object. If the object is not moved, no work is done. The goal of the project relies on efficiently transferring the spring’s energy to the car’s wheels. The concepts involved in the transfer of this energy rely on an understanding of simple machines. The trap acts as a lever to transfer the energy to the axle. The axle acts on the wheel as a second transfer of the energy. Finally, the energy is used to push the wheel against the floor, causing the car to move. Any friction or resistance in the transfer of energy, leads to a decrease in the efficiency of the machine and decreased performance. Keep the use of simple machines in mind as you design the car, the correct use of these machines will increase your performance. Tips Glue: Use a quick drying hobby glue. Pay attention to the drying time specified on the bottle. Some glues will permanently set in as little as five seconds, giving you very little time to position the pieces. If you glue your fingers together (or to the car!) use acetone or nail polish remover to dissolve the glue. You may want to keep some extremely fast drying glue at hand during race day! Wheels: Old CDs make great wheels, but have very little traction. Stretch a wide rubber band around each wheel; the rubber band can even be glued into place. Pull Cord: Your pull cord needs to be strong enough to withstand the forces exerted by the mousetrap spring. Fishing line, rubber bands (not legal in some competitions) or strong string work well. Winding the pull cord in the wrong direction makes the car go backwards; painting a small arrow on the axle as a reminder can help. Alignment: A mousetrap car that always steers to one side will not be good for competition. Place shims (small pieces of scrap wood) in between the bushings or bearings of one or more of the wheels to align the wheels. It is very easy to do this with balsa wood. Aerodynamics: Keep the number of flat surfaces facing the front of the car down to a minimum. Sanding the body of the car smooth also helps cut down drag. Mousetrap Race Scoring 2 Weight of Mousetrap _________________ Weight of Car Goal: Minimize weight Minimize length Maximize distance Distance _______ Length Hints for Better Performance 1. Reduce friction 2. Use lightweight materials 3. Amount of rotational inertia depends on the goal of the car. 4. Test the lever arm length and wheel size to determine the best for your type of car. 5. Experiment early and often Remember Your final score is the total of the following scores: Score on technical report Score on car design drawing Score on the team interview Mousetrap car race score Don’t focus on the car race and forget the others!