Mousetrap Car Blog Reflection

Newton’s first law of motion states, “Every object continues in a state of rest or uniform speed in a straight line unless acted on by a nonzero net force.” In other words, an object will stay at rest until a force is acted upon it and an object will stay in motion unless a force is acted upon it.”  Theoretically, the construction of our mousetrap car seemed pretty simple because the force of the mousetrap would cause our car to move forward and according Newton’s first law to continue moving forward. However, we had to keep in mind the FORCES that would act on our car to prevent it from continuing in motion such as friction. We had to create a force that was larger than the other forces acting on the car.

Newton’s second law of motion states that force causes acceleration therefore force is directly proportional to acceleration and acceleration is inversely proportional to mass. (a=fnet/m). This law was key in our construction of the car. If the force was larger then the acceleration would be larger too. The more acceleration the car has the better chance of the car going the distance of 5 meters and going faster than other cars in the project. Also, we needed to keep a lighter frame and lighter axels for the car so its mass would be less and it would have a greater acceleration.

Newton’s Third Law states that every action has an equal and opposite reaction. Newton’s second law can be explained in the formula  (a=Fnet/m)which explains that acceleration is directly proportional to force and indirectly proportional to mass. Newton’s Third Law can use this same formula but you can write it in a different way: (F=ma). The fact that every action has an equal and opposite reaction was important for our car because we needed keep in mind that no matter what the ground would pull down on the car and the car would pull up the ground with an equal and opposite force, so the car needed to be strong.  For example if this was our mouse trap car; Car F (10N) =mA the force would be the same either way, but to control the distance and speed the car went we would need to increase the acceleration rather than its mass.

The two frictions present in this project were static and kinetic friction. Friction played a big role in a project with its advantages as well as its disadvantages. When constructing the car, we had to take into account the level of friction we wanted the car to have on its wheels. At first, I thought it would make more sense to have the least amount of friction on the wheels as possible because according to Newton’s first law an object will stay in motion until a force is acted upon it. (I thought friction would only be a disadvantage.) So, I thought if there was no friction on the wheels there would be no force acting on our car and it would keep moving. However, I soon realized that friction on the wheels would be vital for our car to move. We put friction on the back wheels so the car would be able to have traction to move across the floor. Otherwise the wheels would just have been spinning without going anywhere. However, we did not put any type of friction on the front wheels to allow the wheels to spin freely and quickly. In this way friction was used to our advantage. Finding the materials to use to create enough friction on the back wheels but not too much was also a challenge. But after doing some research, wrapping cut up balloons around the back wheels seemed to be the best solution.

We chose to do four wheels for our mousetrap car because we thought four wheels would give our car the best stability. At first, we planned to make the back wheels larger than the front wheels, however, in the end we decided to use four discs. The back wheels were CDs and the front wheels were DVDs. This was because the DVDs were significantly lighter than CDs, so we wanted to have less mass on the front axel so the wheels could move more quickly with a lighter mass whereas the back wheels (attached to the back axel) needed to be heavier for the level of friction and mass. Extremely large wheels seemed like a good idea because they could cover a greater distance in a shorter amount of time and the small wheels seemed like a good idea because they could move faster in a shorter amount of time. This is why we originally had our car designed this way. However, we found a moderate balance with the CDs and DVDs and decided to focus more on the mass rather than the size. We wanted to keep the design simple and the equal sized wheels made it easier to do so.

The conservation of energy states that energy cannot be created or destroyed; it may be transformed from one form into another; but the total amount of energy never changes. When you think of a system, like a swinging pendulum, there is one thing that is neither created nor destroyed, and that would be energy. The energy may change form, for example, it may turn into heat, however, that does not mean the energy is lost. Take a water dam for instance. The water behind a dam has energy that may be used to power a generating plant below, where it will be transformed to electric energy. The energy will then travel through wires to homes where it can be used for everyday uses. Because we know energy does not disappear or appear, it transforms, we can assume that kinetic and potential energy can transform into one another. This is similar to our mousetrap car. After considering this concept, we knew that the energy in the mousetrap car would be the energy we would be working with no matter what. We could not increase the energy or decrease the energy of the system. However, we could use it more efficiently by storing enough potential energy in the car for the car to transform into the kinetic energy allowing it to go the full 5m. The whole system would have the same amount of energy in the beginning and in the end.

The length of our level arm was a HUGE obstacle in the construction of our car. At first, we started out with no level arm besides string, which we made twice the length of our car. However, our car didn’t move. So a student at UNCA explained to us that the longer the lever arm, the farther our car would go. So, we used a plastic stick (part of a hanger) and attached it to our car. The first run with this lever arm our car went 5m! After trying it again though, the car struggled to go half the distance. It was frustrating and we thought maybe if we made the lever arm longer it would help, but this just made the car topple over and it even did a complete flip in one test run. Then we tried to balance our lever arm so it was more centered. But again the lever arm was just not working for us so we took it off and just used the string; this time the string was much shorter. We also made our axels thinner. If we had constructed the lever arm in a different way, the car may have gone 5m, however, it just did not work for us. So our pulling force was simply the string coming forward with the mousetrap device and pulling the back axel forward causing the back wheels to spin forward.

Rotational velocity is the number of complete rotations per time unit. We wanted our front wheels to have a high rotational velocity meaning it would have more rotations per time unit whereas the back wheels could have a greater tangential velocity. Tangential velocity can also be called linear speed because it is something moving along a circular path. The direction of motion is tangent to the circumference. Tangential speed depends on the distance from the axis of rotation. Inertia is the property of an object to resist change in motion dependant upon the mass. This was important in the construction of our wheels because the larger the wheels the greater distance these wheels would cover in a shorter amount of time even though they would have a smaller rotational velocity.  Rotational inertia is the property of an object to resist changes in the spin of an object. It is dependant upon, not the mass of each object, but where the mass is located on that object, how it is distributed.  It involves the distribution of mass and how far away it is from the axis of rotation. If an object has a small amount of rotational inertia, it is easier to spin compared to an object with a large amount of rotational inertia, which is very difficult to spin. We set up the wheels pretty close together because the less distance the faster the wheels would go.  We also had to make sure we didn’t have the a lot of weight spread out on the car, this is why we used the frame of the car to simply be the mousetrap because it would create a smaller mass that was together creating less rotational inertia on the car. The less rotational inertia our car had the better.

Work is the effort exerted on something that will change its energy. Work equals force times distance. [Work=Force X Distance] Work is measured in Joules. The force and distance must be parallel to one another in order for there to be work done. We cannot calculate the work being done on the spring because the spring is not parallel to the distance the car travels. Potential energy is energy that is stored and held in a stored state that has POTENTIAL of doing work. Potential energy is equal to the combination (multiplied) of mass, gravity, and height.[Potential Energy= Mass X Gravity X Height] We cannot calculate the amount of potential energy being done on the spring because we don’t know it’s mass or its height. Also, we can’t measure don’t know the total energy of the system so it’s not possible to calculate the potential energy. Kinetic energy is the energy of motion. Potential energy can change into kinetic energy. The change in kinetic energy of a moving object depends on the mass of the object as well as its speed. [Change in Kinetic Energy=1/2mass X velocity^2] Anything in motion has kinetic energy. According to the work energy theorem, work equals change in kinetic energy. The change in kinetic energy can’t be measure on the spring because we don’t have enough evidence of the velocity of the spring itself. Acceleration is equal to speed times distance, although we can measure the acceleration of the car, we cannot measure the acceleration of the spring because we don’t know the distance it traveled nor do we know the speed it traveled.  

Our final design was much different compared to our original design. Our original design is in the picture in the blog post before this one. Our final design had a much more simple layout. We learned the smaller the axels and the smaller the mass of the system in general the more functional our car turned out to be. Stability and simplicity were the main goals we had to achieve in order for our car to work, which is why we made a frame for the wheels on our final car.

The mousetrap car was definitely a major struggle for our group partly because our car worked on Friday and then over the weekend it somehow stopped working and forced us to completely start over with the car. We struggled a lot with the lever arm because according to concepts of physics we learned in the past, the longer lever arm the farther the distance the car would go. However, with our car the longer the lever arm the less our car functioned. So we had to take away the lever arm and use string. Also, we struggled a lot with stability. The wheels of our car seemed very shaky especially the front wheels. They kept sliding around causing the car to run into the wall. So, we had to use part of a pen to prevent the front wheels from moving but that took a lot of experimenting and sawing to figure that piece of the puzzle out. Lastly, simplicity is what our design struggled with. We were told that increasing the back axel would help the speed of the car. We used a cork to wrap the string around it but this cork may have been the foundation of our problems. The string let out too quickly so our car couldn’t reach its full energy level. In the end, we had thinner axels (without the cork) and no lever arm and our car went the required distance and it went fast.

If we were to do this project again, I would definitely take the factors of simplicity and stability into account and try to work with those more efficiently. Also, I think the longer lever arm could really help the car go a farther distance, I just think it needs to be constructed differently so the car is more stable. Also, the axel issue seemed like the cork should be extremely helpful with the speed and although it had a negative affect I would like to try and figure out a way to use the thicker back axel and still have the string let out at an equal pace instead of all at once. I think if we re did this project we could really make outstanding cars.