In this unit, we had to build a car that used an alternative source of energy other than stored electrical energy. My group consisted of Kendal, Caitlin, and Beau. Our car would be judged on how far it can go (at least 5 meters), how close to the target our vehicle would stop, how fast the vehicle can carry 250 grams, our 3 to 5 minute presentation, and how cost efficient our prototype is to build. Our original idea for a source of energy was to use a Diet Coke and Mentos reaction to power a waterwheel. When you mix Diet Coke and Mentos together, the reaction between the two creates a very fizzy explosion. We planned to use the force of this eruption to power the waterwheel, which would be on the ground, to move our car forward. We worked on this plan for the entire build period, but on the last day of building, we found out it didn't work.
Since we already had a waterwheel, we then tried water in place of the Diet Coke, but that also didn't work. We moved on to our last idea, which was to use rubber bands. Since that was our last building day, we worked in during lunch to finish the car. We finally finished our third car, only one day after the last build day. We got lucky, and our car traveled five meters on its first try.
Concepts we used in our Hybrid Car Battery Design:
Spring Potential Energy - Energy stored in a spring or elastic by pulling or pushing it. We calculated the spring potential energy for the rubber band powering the car. It is calculated by PEe=1/2kx^2. x=distance moved by spring.
Spring Constant - A measure of how much a spring wants to pull back together or the rigidity of the spring. It is calculated by k=F/d. If it is easy to move, it would have a low spring constant, and if it were hard to move, it would have a high spring constant.
Speed - How fast an object moves. It is calculated by S=d/t. The average speed of our car was .75 meters per second, or 1.68 miles per hour.
Thermal Energy - Energy created by heat, usually because of friction. It is calculated by total energy - KE - PE. On our performance graph, our car started off with little thermal energy, but gained more as the car went farther, because it lost more and more potential and kinetic energy.
Here are our car's performance graphs.
Pits and Peaks of our project
I think out of our entire STEM class, our group got the most learning and experience out of this project because we built one car that didn't work, and one car that did work, and we learned from both. This was our third STEM project, and it had a couple pits and peaks. My first pit was how we wasted time on ideas that weren't working. Our first idea took the entire building process, and the Diet Coke and Mentos car didn't even end up working. We had to build our rubber band car in an hour with a board that was for a much bigger car. Looking back, we should have tested the Diet Coke and Mentos reaction first, to see if it would power the waterwheel sufficiently. Or, if we had done our rubber band car at the beginning, our car would've been much better, because we would have had much more time to modify and adjust it more. Even though our original plan didn't work, it was still fun to build it and see if it would work. My first peak was how well our group communicated. We were all open to each others ideas. We also all did about an equal amount of work throughout building the two cars. Everyone was able to stay on task because we had enough work divided between us, with the slideshow, the calculations, and the actual building. My second pit was our time management. We didn't have a completely planned out schematic for our Diet Coke and Mentos car, or our rubber bands car. Since we didn't have a planned out schematic, we weren't sure if our car was going to work. If we had, we might have realized that and moved on to our second plan. Inadequate time management meant that we had less time to work on the presentation and calculations, which made our presentation fall short of the other groups. My second peak was our productivity. After our Diet Coke and Mentos car failed, we worked fast and hard to finish our rubber bands car. We were amazingly able to finish it only one day into the presentation and calculations making process. Even though we spent less time on our second car, our car still worked as well as the other cars.