For this project, I assignment was to build a car using an alternative power source that would only run exactly 5 meters carrying 250 grams. One group used a rat rack, one used a lever, and most of the groups used rubber bands, like my group did. At first we built a wooden frame (using hot glue) with a plastic axle, attached to two rubber front and back wheels. On our first try we wrapped the rubber band around the axle as much as possible without snapping it and let it go, but unfortunately it didn't even go at least half the distance and the plastic axle was beginning to slightly bend. We came up with a solution, and that was to replace the plastic axle with a copper one and to replace the front wheels with CDs to make the car go a greater distance. We quickly discovered that since the CDs were so thin, they didn't have enough contact with the ground so they would spin out resulting in not even one meter of distance traveled. For our last adjustments we added tire threads onto the CDs for more friction, dissembled the wooden frame and started over with completely new pieces but this time attached it with screws to make it more sturdy, and we also started to use a a bigger rubber band that would give us more rotations around the axle resulting in more distance. After all the tweaking, our car finally worked! Our car would go on an average of 4.7 to 5.2 meters with ten rotations of the rubber band going around the axle.
Concepts
Spring Constant- Spring constant is the measure of elastically of an object. To find the sprin constant ina n object the equation is F= kx. Our spring constant was 2.25 N/m.
Gravitational Potential Energy- This is the amount of energy and object has before going in motion duw to gravity. Gravitational potential energy can be found from the equation PE=mgh (mass x gravity x height). Our car's potential energy was 5.5J. Kinetic Energy- Kinetic energy is how much energy and object has due to motion. It is calculated by taking half of the product of mass and velocity squared (KE= 1/2mv^2). After passing each meter, our kinetic energy slowly decreased. Thermal Energy- Thermal energy is the lost energy during the transfer of potential energy to kinetic. Th thermal energy increased as the car passed each meter. Spring Potential Energy- This is energy due to compression or expansion of an elastic material. This is found with the equation of PEs= 1/2kx^2. The spring potential energy was 0.23J. Velocity- This is speed with a given direction. Velocity can be found by dividing distance over time (V=d/t). Our car increases in velocity then reached the third meter and slowly decreased. Friction- This is the force that affects motion. For our car, the CDs didn't have enough friction so we added the tire threads to increase it.
Reflection
This project was very fun but also challenging! The fun part was building your own car from scratch and getting creative with the materials, but the challenging part was finding new solutions if your original ones didn't work. Pits in my group was that half of us were focused on the project and the other half were off task and not contributing. I tried confronting them about it and they started to contribute more that really helped towards the end. I learned that its better to tell the person what the issue is rather than complain about it and get nothing done. Another pit was definitely time management. We were rushing on the last building day to get our car to work which was really stressful and it could of been avoided. Maybe next time, before starting the building process, we can all sketch out exactly what the plan is and what is need and who does what so we know exactly what we're doing everyday. A peak was that I learned to be more creative. With so many things not working properly on our first model it really forced me to think "outside the box" and come up with new ideas. Another peak was that our car was the closet to stop at exactly five meters in our class. I really enjoyed this assignment, and it was a great experience!