In the end, our car clocked in at an impressive 0 m/s. However, I still learned oceans about physics from this project. I also learned good problem solving skills that I will need later on in my life. Here are the physics of the mousetrap car that I learned:
Newton's Laws can be applied to this car. Newton's 1st law, which states that an object in motion will stay in motion until an outside force acts on it (and the converse for an object at rest), means that if we decrease the possibility for outside forces to interact with our car, we will increase its odds of reaching the finish line. Newton's Second Law states that Acceleration is proportional to Fnet and inversely proportional to Mass, therefore, the more we decrease the mass, the better the acceleration of the car will be. This led us to use the lightest possible materials, such as wooden skewers and paper towels. Newton's Third Law states that for ever action there is an equal and opposite reaction. We applied this aspect of physics to our lever system. We knew we had to decrease the friction between the string and the axis, so we tied the string to the axis in a quadruple under over knot, and taped it as tightly as possible.
Two types of Friction that were present in the making of this car were air resistance and surface friction. Air resistance is difficult to change because the faster the car goes, the more air resistance there is. However, we could decrease air resistance on the car by decreasing the surface area. We did this by taping down all loose paper towels to make sure there was nothing that could spread out and increase the surface. We used surface friction to our advantage. Initially, CD's seemed like a bad choice for wheels. However, once we covered them in duct tape and increased the friction on the ground, the car moved very smoothly.
It didn't take much thought to decide which wheels we would use. We knew CD's would be a great choice because they have a very low rotational inertia due to the fact that the mass is evenly distributed throughout. This meant that they would be easy to get moving. Also, the fact that they are larger than, RC Car wheels, for instance, means that they have more mass, giving them more rotational velocity. We chose to use 4 wheels simply because it was all we had room for.
The Law of Conservation of Energy (Force in X Distance in = Force out X Distance out) played a large role in the making of the mousetrap car. We knew that if we made the lever arm very long, in addition to increasing the force, we would see a long distance output and strong force output. It is for this reason that we decided to make our lever arm out of 3 wooden skewers taped together tightly. This gave the lever arm strength and length, increasing our work output twofold, and making the car very efficient.
The work done by the spring was impossible to calculate because we could not calculate the Force (weight) of the spring, and Work = Force X Distance. Calculating the force of the spring would involve removing the spring and actually weighing it, which would render our mousetrap unusable. We also cannot calculate the amount of Potential Energy on the spring because PE = mgh, and the height of the spring is minuscule throughout its path, and changing very quickly, making it very hard to take into account. Thus, we cannot calculate the Kinetic Energy on the car. We cannot calculate the Force the spring exerted because we cannot find the mass of the spring to use the equation A = Fnet/m
The final product of this project was very different from our original design. The biggest difference was that our wheels were more stable than they ever were. We had to apply many feet of tape to the car to make this change. We still encountered many problems, for example, the wheels did not have enough friction on the axis to move as quickly as the axis moved. Because of this, the wheels simply wouldn't move when we set the mousetrap off. This problem never got fixed, but it was probably due to the makeshift axis. In the future, I would like to have more time for planning, and also more supplies. I feel like I entered this project blind as to how to make one of these cars.
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