Mousetrap Race Car Challenge

Our car came in second place and went five meters in 4.75 seconds.

Building our mousetrap race car was very challenging, but the hardest part was determining the ways in which so many different physics concepts could apply to one thing. All three of Newton's laws applied. The first, newton's law of inertia, applied because all we had to do was find a way to set the object the object in motion. This is because the law of inertia states that an object in motion will stay in motion unless acted upon by an outside force. We knew there was already an outside force that would be acting on the object, that was friction, therefore we also knew that we needed to set the object in motion long enough for the car to roll 5 meters without the car stopping. Newton's second law, the law that states that acceleration is directly proportional to force and inversely proportional to mass. So we knew we had to make the car as light as possible and the force that set it in motion as strong as possible for maximum acceleration. Newtons third law, the law that every action has an equal and opposite reaction easily applied because it also showed us that we needed to have a big force when the mousetrap closed in order to move the car a full five meters. All three of these things helped a lot in the initial thinking about how we were going to design our car. 

Friction played a huge part in building our car. One problem was that the less friction then the longer the object would stay in motion without being stopped by the friction. Another problem was that the more friction we had the more grip it would have on the ground to roll quickly. Since we needed both distance and speed, we put friction only in the back by wrapping balloons around the edges and no friction on the front wheels so that the car would roll with some force but be basically frictionless in the front. We had to take friction into account when looking at how to get as little friction as possible between the wheel and the body of the car and the friction of the wheels and the ground. 

We had to take many factors in when deciding how many wheels to use and what sizes we would make the front and back wheels. We had to look at rotational inertia, rotational velocity, and tangential velocity into account. We knew that the car would balance the best on four wheels and that that would be most effective when it came to turning the axle, so that's what we went with. We had trouble deciding between small wheels in the front and big wheels in the back or the same size wheels on every side of the axle, but we knew that the car would go more straight and therefore cover less amount of distance if all the wheels were the same size. We also knew that the bigger the wheels were the bigger tangential velocity they had and we wanted as big of velocity as possible so we went with four big wheels. 

The conservation of energy law says that no energy is every lost or destroyed it is simply converted. This is proven when it comes to our car because when the mouse trap is set there is an large amount of potential energy due to tension between the metal bar and the lever arm and the string that is attached to the end of the lever arm. When the mousetrap is released, the potential energy begins to convert to kinetic energy as the car does work and moves forward. 

The length of our lever arm was about 5 inches long. We attached two 5 inch long wires (from a wirer hanger) to the sides of the part of the mousetrap that needs to be pulled back in order to be set and hot glued and taped them on to make them secure. At first we had a very long lever arm that was only on one side of the part of the mousetrap, however that did not work. In fact, the shorter we made our lever arm, after we added one to the other side, the longer it went because the faster it was able to pull the string forward and therefore the wheel. This is because the shorter it was the more pulling force it was able to have. The more force, the faster it went. Since the work is always the same shortening the lever arm shortened the time and therefore increasing the power produced. 

Rotational inertia, rotational velocity, and tangential velocity all played parts in the functioning of my car when it came to the wheels. The more weight we had at the center of the wheels, the less rotational inertia and therefore the more likely it was to spin. Thats why we put tap, which is relatively heavy, and super glued the wheels to the tape to add weight. The rotational velocity of the wheels was all the same because we had the same sized wheels. The tangential velocity of the wheels was greater than it would have been if we had used two small wheels and two big wheels because instead we just used two big wheels and the farther away it is from the center the faster it goes. All of these things helped to improve the speed of our car. 

The reason that we are not able to calculate the amount of work the spring does on the car is because the force applied and the distance it goes are not parallel, and when the force and the distance are not parallel no work is done. The reason we can't calculate the amount of potential energy that was stored in the spring is because not only do we not know its mass but we also do not know its height. The reason we can't calculate the kinetic energy is because we do not know the velocity of the car. We can not calculate the force the spring exerted on the car to accelerate it because there was a lever arm and also we don't know the mass of the spring or the speed of the car so we can not calculate how much it was accelerated. 

 

Reflection

     Our final design was completely different from our original design. What promoted these changes was mainly that we changed the car in order to make it travel the full 5 meters. We stabilized the wheels, made the wheels have less friction by removing tape and adding balloons to the back wheels, and shorted the lever arm to increase the force that pulled the string. The majors problems that we encountered in the performance of our car was that for a while it would only travel about half of the 5 meters. The lever arm was way to long at first and we didn't understand why it wasn't working. It took a lot of patience and researching what was the problem with our car. 

    If we were to do this project again, I would first not have my mousetrap glued to anything and instead just have made the mousetrap the main body of the car. I also would have done what the group with the fastest car did and not have a lever arm to save time and supplies. 

Unit 5 Reflection

In this unit the first thing I learned about was work. Work is the ability an object has to do something and the equation for work is force times distance. The most important thing I learned about work is that the force and distance must be parallel, otherwise there is no work being done. The units for watts are joules and since work never changes the bigger the distance the smaller the force or the bigger the force the smaller the distance. For example,

w=df
w=df
The second thing I learned about was power. The formula for power is work over time. The units for power are watts which one watt equals one joule over one second. Power measures energy. Cars are measured in horse power, and one horse power is equal to 746 watts. Therefore, it is possible to create a horsepower if you can create 746 watts of power.
The third thing I learned about was kinetic energy. Kinetic energy is the amount of energy an object is using and is directly related to not only work but potential energy. The kinetic energy of an object depends no the mass of the object as well as its speed. The formula for kinetic energy is 1/2 times mass times velocity squared. This means that if the velocity is tripled, the kinetic energy will increase nine times because the velocity is squared. The relationship between work and kinetic energy is that the change is kinetic over time equals the work done. The relationship between kinetic energy and potential energy is that the higher an object goes, the more potential energy it has. The lower it goes/falls the more potential energy it looses and kinetic energy it gains. The formula for finding an objects potential energy is mass times gravity times height.
    The fourth thing I learned about was the Law of Conservation of Energy which 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. This means that in a car the energy used to move the car forward does not disappear it is mearly converted into heat.
    The fifth thing I learned about was machines. Machines help lower the force needed to move an object. The big thing about machines is that there is a work in and a work out. The work out is what force and distance you would have to do without a ramp or a pulley and the work in is the smaller force and bigger distance you would have to do with a ramp or a pulley.
     What I have found difficult about what we have studied this unit is keeping all the different formulas straight and remembering that the change in kinetic energy equals work and not just the kinetic energy. I over came these difficulties by doing problems in class and memorizing which formulas were associated with which concepts so I knew which ones I needed to use. My problem solving skills and effort this unit have not been as strong as they usually are. Though I have completed all my homework and really tried to understand our activities, I have not been persistent in learning the materials and my self-confidence lowered as a result because I did not do very well on quizzes.
     My goal for the next unit is to be persistent in learning things that may prove to be difficult and memorizing the formulas right when we learn them so that I do not struggle throughout the unit and instead can attack each new concept with out having to worry about the last.
     The connections that I can make to the real world are with the three flights of stairs every day versus the elevator on the other side of the building. It is good to know that I get a work out instead of a work in. Another connection I can make is to cars, both with the law of conservation of energy and power. Since my dad is a car dealer I know a thing or two about the engine and it is interesting to understand that the reason cars aren't 100% efficient isn't because any energy is wasted but rather because it is converted into heat.

   

Unit five photo

If a person wanted to get a ball that weighed 200 newtons from the bottom of the arch way to the platform in the middle of the stairs, it would be easier for them to bring it up the stairs rather than throw it. This is because the vertical distance that it will travel will not change, therefore the work will not change. If the work doesn't change, that means that the greater distance the smaller the force. Therefore, because the stairs are a greater distance than the arch way, the force needed to get from the bottom of the stairs to the platform would be way less than if you threw it.