Mousetrap Car

Newton’s First Law states that an object at rest wants to stay at rest and an object in motion wants to stay in motion unless an outside force acts on it. Newton’s first law can be observed in a mousetrap car because is evident that the car does not want to move until an outside force acts on it, and then it takes another outside force to make it stop moving, the force of friction. Newton’s second Law states that a = Fnet/m. That Law is also noticeable in the cars because none of the cars of our class were heavy. All of the students made their cars light and that works because the more massive your car is the smaller the acceleration will be. Newton’s third Law states that for every action there is an equal and opposite reaction. As the mousetrap car moved across the floor, gravity was pushing it down and the car was pushing the floor up also, car pushes floor backward, floor pushes car forward. My partner and I decided to use four wheels to keep the car balanced; its center of mass needs to be under its base. We first chose to use small wheels but after many failed trials we decided to switch them to large wheels. Large wheels worked better because they have less rotational inertia so they are easier to start and they are a lot more stable. They have less rotational inertia because their mass is more evenly distributed. Friction between the wheels and the floor is necessary to propel the car forward but air resistance or the lever arm dragging on the floor is something you want to avoid. Conservation of energy means that the energy in is equal to the energy out. On the mousetrap car the extended lever adds Potential Energy to the car. When the mousetrap car is moving the lever arm moves down losing potential energy and gaining Kinetic Energy that through the string attached to the axle of the car is used to turn it and move the car. We first started using a short lever arm and at the end we decided to use a lever arm a lot longer than the first one. A longer lever pulls more string and that makes the axle spin better. The farther the string is pulled the more energy is given to the axles.Rotational inertia and velocity are a factor when it comes to the wheels of the car. You do not want the wheels to be like a loop because that would make the concentration of mass be in the outer part of the wheel increasing the rotational inertia. The more rotational inertial something has, the more resistant to a change in motion it will be. Tangential velocity has to do with the radial distance and rotational velocity, the larger the wheel the more tangential velocity it will have. The rotational velocity also needs to be as great as possible, that means the axle needs to spin fast! With the combination of a big wheel and an axle that spins fast, the wheels should have a great tangential velocity.

Reflection:
Our design changed a lot from the begging of the project to the end. The size of the wheels were the main change. We started with small wheels that did not even make the car move at all. After that we change to large wheels on the back and small wheels on the front. We found that in order for the string to spin the axle, it had to be taped to the axle and that a larger lever arm is more effective than a short one. The changes were made because our original design was not causing the car to move. Another big problem we’ve encountered was making the wheels stables enough. By using only tape and cardboard wheels it is difficult to make the wheels stay in place. The solution we found to this problem was to tape the wheels to the axle on the outside and inside of them. If I had to do this project again I would start with large wheels a large lever and a more stable base. I would also spend more time planing which materials to use so it would save me time on the construction.