The assignment was to create an alternative energy car that we would present to Hundai in a sales pitch for them to begin producing. We were restricted from using chemical energy. This meant no chemical reactions(such as mentos in coke) or batteries. The car was supposed to get as close to five meters as possible, while carrying a 250 gram mass. As a group we considered using a carbon dioxide cartrtidge, but then decided it would be much too unpredictable. Then we settled on a spring powered car. One end of the spring is attached to the front of the car, and the other end to a string. The rear axle has a small hole drilled through the middle. The string is threaded through the hole and the axle can be turned to wind up the car.
Building Process
We began with the largest block of wood that you can see forms the main body of the car. We drilled two holes for the axles, and cut out a section in the back of the body so that the string could be wound up. We then screwed small lego wheels onto each axle. We experimented with using multiple small springs, but found it much simpler to use the one big spring. The spring was attached to the front of the large block. We found that something called the nascar effect was taking place, when the sudden acceleration of the wheels does not allow them to bite and actually move the car, basically, it was burning out. We then began adding weights and found that it helped very significantly. We also noticed that it still wasn't going very far. We decided to add bigger wheels in the back to give us more mechanical advantage. For each time the axle spins, it moved the car farther than before. The last problem that we had was that the spring did not have quite enough power to take the car all the way to the five meter mark. We added the peg on the front of the car so that the spring could be stretched farther and provide more power. Last we created our presentation, which can be seen here.
Concepts
Spring Constant- Spring constant measures how much force is required to expand and compress a spring. It is measured in Newton meters, or newtons per meter, and is represented by a lower case 'k'. We found the spring constant of our spring by using the equation k=f/d, or spring constant equals force divided by distance; the force being the force applied to the spring, and the distance how far it moved. We found that the spring constant of our spring to be 150 newtons per meter.
Spring Potential Energy- Spring potential energy is the energy that is created and stored when a spring is compressed or expanded. We can calculate it by using this equation: PEs=kx^2 or spring potential energy equals the spring constant times the distance moved by the spring squared. We found the potential energy at the beginning and at each meter, and you can see it in the graph below.
Kinetic Energy- Kinetic energy is described as energy due to motion. The equation that we can use to solve for kinetic energy is KE=1/2mv^2. Put into words, this is kinetic energy equals one half mass times velocity squared. This means that the higher the mass and the velocity of an object, the higher its kinetic energy will be. We measured the mass of the car, and its velocity at each meter, then plugged it into the equation to find the kinetic energy.
Thermal Energy- Thermal energy is the third main type of energy besides potential and kinetic. It is any energy that is lost to heat, so it was mostly through friction in this case. The way that we found the thermal energy acting on the car is by taking the potential energy at the beginning, which will be the total energy the whole time that the car is running. Then we subtracted out the remaining potential energy and the kinetic energy at each meter.
Here is our energy versus time graph. Here you can see the changes in energy, and what energy was having effect at each second. You can see the the potential energy, in blue, starts out very high because the spring is completely wound up, then drops rapidly as the spring compresses. The kinetic energy starts at zero, slowly builds to about a jewel as the car gains speed, then decreases as the car slows down. The thermal energy, or friction, starts very low, then shoots up, as it accounts for all loss of kinetic energy.
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Project Reflection
We had a lot of highs and lows in this project. Moments when we thought it would be a complete success and moments when we thought it would fail. One of the lows that I personally had was when we were deciding what kind of model our car would be, and we had some trouble coming to a decision. I did not have a good outlook on our project, and was thinking that we would not get very much work done. Each of us had varying opinions on what would work best. However, it did turn out pretty good. Another low in my opinion was when we did our first test run, and the car didn't go anywhere. This was when we had been using multiple small springs. For a little while, I honestly thought that there was no way that the car could work. One of the highs in this project immediately followed this, when we replaced the four small springs with the one larger one. I realized that our car had a very good chance of successfully doing the five meters. I was very optimistic at that point because I had also noticed that my group was beginning to work really well together and we were collaborating well. A second peak that I had during this process was when one of our test runs got really close to the five meter mark and I knew in a moment that our car would turn out near perfect.
There are a couple things that I think I could have done better during this project. Once again, my communication has been improving over time, but I know that I can further the progress. I intend to continue working on that, as it is an extremely important aspect of group work. Another thing that I can better is my positivity. I have found that when I am positive, I am more productive. If I work at staying positive, hopefully it will help me get more work done.
There are a couple things that I think I could have done better during this project. Once again, my communication has been improving over time, but I know that I can further the progress. I intend to continue working on that, as it is an extremely important aspect of group work. Another thing that I can better is my positivity. I have found that when I am positive, I am more productive. If I work at staying positive, hopefully it will help me get more work done.