Mousetrap Car Reflection

For the last few days, we have been working on making a car using a mousetrap to propel it. Our goal has been to make a car that goes five meters, and preferably with speed.
Yesterday we raced our cars, and here were the results:


Our car went an average velocity of .60 m/s.
(velocity = distance/time)
Distance: 5m
Time: 8.2 seconds
We came in last for our class as far as I know.

Here is a picture of the car we made:

and here is a diagram of it to make the individual parts clearer to see for reference when reading the following reflection.

Here is a video of our trial of our car going:


Reflection:

a.) Newton's First Law sates that an object in motion stays in motion unless acted upon by an outside force. In this case, the outside force is primarily Friction. The friction is needed to get the car going, you must utilize it to get it from going to not moving to moving. But you don't want so much that it also makes it go from moving to not moving.

Newton's Second Law states that Acceleration = Force/Mass. For this, you need a large Force which is the spring to provide the force to cause acceleration. Too large of a mass, however, would lower the acceleration, but you must consider that the mass contributes to friction, so you do need some.

Newton's Third Law states that every action has an equal and opposite reaction. In this case, the most relevant action/reaction pair is Wheel pushes on ground, ground pushes on wheel (you can see this drawn on the diagram above in green). The Force that is a part of the work that the wheel does when pushing on the ground is the Force causing acceleration. As we know from the previous two laws, that Force is important to how quickly the car accelerate, and also the friction of that action is important in starting the car quickly as well.

b.) The main part of the car that relied on Friction was the wheels, specifically the part that made contact with the ground. This friction was the Force that acted on the car so that it could go from not moving to moving. the more friction there was there, the easier it was for it to go from not moving to moving. For this friction, we wanted it to be more than just the edge of the CD because that did't have much friction. We instead put some electric tape in the edges so that it would have more friction. We didn't want to have too much friction there either or else it would slow down the car as well (be the force that made it go from moving to not moving quickly as the car lost speed). We thought the electric tape would be a good balance. Another part of the car that valued friction was the place where the string coiled around the axel. the more friction this part had, the faster the string would spin the axel as it unraveled. We did not have the time or wherewithal to tinker with this part, but I imagine it may have made our car go faster.

c.) We decided to choose a medium sized wheel in our CDs. We did not think this through particularly well, however, we figured that moderate was the best way to go for this project. It turns out we were right to assume because Bigger wheels actually crate a bigger lever arm which means there is more torque. However, it cannot just be as big as possible because the bigger it is the more rotational inertia it has which will make it more reluctant to rotate. So a medium size like CDs accommodates both the hinderance and the advantage of wheel size.

d.) The Energy of the car is put in as we pull the lever arm/ set the mousetrap, and it is stored in the spring until you release it. The energy stored in the spring is Potential Energy. Once you let the spring spring back, the Potential Energy turns into Kinetic Energy. This Energy is conserved as it converts. For instance, if we knew we stored 100J of Potential Energy in the spring when we pulled it back, then at the end of its route, the lever arm then has 100J of Kinetic Energy. In our car, we had a wooden lever arm that was attached to the mousetrap, when we pulled it back, we coiled the string attached to it around the axel in the back. When we released the lever arm, the potential energy converted to Kinetic Energy as it swung back towards the front and spun the wheel as it gathered kinetic energy.

e.) We First Knew that we didn't want the wheels to be too heavy because having more mass would mean there would be more rotational inertia. This would make the wheels reluctant to rotate, and thus reluctant to move. We also wanted to make the torque of the wheel (the radius) fairly big to make the rotational inertia lower. When we make the lever arm bigger, we would make the force needed smaller. But because we didn't want it too big because of the aforementioned inertia problem. SO we got a medium size wheel. Theoretically, the wheel is going to be spun the same amount of times every time we pull the spring back and let it loose. So when we have a larger wheel, it will cover more distance in the same rotation which is another reason to make the wheel a little bigger.

f.) We cannot calculate work that the spring does on the car because the work it does is not parallel but rather perpendicular to the distance the car goes. The force it does goes towards the ground, and the distance the car travels is forwards. In the same vain, The potential Energy that gets stored in the spring when we pull back gets converted into kinetic energy, but that energy does not go into propelling the car forward because the Force that is in the Kinetic Energy is not parallel to the distance either. We can't calculate the force that accelerate's the car because the Force that accelerates the car is not related to the other equations we do have the information for. So we cannot put the thing we do know about how it went forward, the distance, and find the force because we cannot use the work or KE equation as they are not parallel.

Reflection: 

a.)   Our initial design was fairly similar to our final design. We had to change many things, such as the lever arm and the string, but they were not drastic design changes we just had to make them better. If we could do the project again, the design would change, but I think we mostly adapted our design in the interest of time. We did look at other people's cars and add tape to the edges of the wheels for friction and we also stabilized our wheels fixed to the axels instead of loose around them by the suggestion of Veronica and Alex.

b.) One of the major problems was that it simply did not go far enough. The spring did not pull our axis like we thought it would when we first tested the car. We first realized that we hadn't put both of the little activators that stuck out from the spring on top of the lever arm. So when we did that we basically doubled the PE. That really helped. Then we also shortened the string and lever arm and finally got it to go further. Also our body was very flimsy as we tinkered with it it would bend on accident so we had to tape a wooden stick to it on the bottom and top so that it would be more stable and we wouldn't lose the energy in the spring going into bending the base.

c.) I would make the car longer and thinner and out of sturdier material. I would take more care with the axel wheel relationship because ours was sloppier than I would have liked and I think we lost a lot of energy there. Also make better use of the leveler because ours seemed wobbly. I think I would also try to only put friction on the pack wheels which are attached to the string.

d.) I might take more care with the preliminary steps to ensure that I was less likely to have to repeat certain parts because they were not done well the first time. In that same thought, I should worry much less about time and not feel rushed. Haste makes waste. Also some thought into which design to choose would be helpful because we sort of chose the first one that looked good. And also get materials in on time.