Final Mousetrap Car Blog

Our car (Zach and Nolan) went 5 meters in 4.28 seconds (3rd p
lace).

      At first, we used a very long frame made out of wood because we were initially going to use records for the rear wheels, but the records broke so we had to cut most of the frame off. We used a short, wooden frame because it is both light and sturdy, so that the trap does not have to use that much force in moving the car (mass determines resistance to acceleration). We used four CD's as our wheels because they were thinner and that meant less friction on the ground when it is rolling. Also the larger wheels will have a greater tangential velocity. We put balloons on the rear wheels for traction, because the balloons have more friction than the plastic CD's. We used wooden dowels for the axels because they were light and effective and connected to the wheels. We used another wooden dowel for the lever arm that attached to the trap, because it was sturdy and we could cut it if necessary. We also used gorilla glue throughout the whole car because it dries fast and is light.

      Newton's first law states that an object in motion stays in motion and an object at rest stays at rest unless acted on by an outside force. This relates to our car because our car would stay in motion unless acted on by friction or even the wall if it hits it. Newton's second law states that A=Fnet/m, or acceleration is inversely proportional to mass and directly proportional to force. This relates to our car because the heavier our car is, the slower it will accelerate. For example, we first had a lot of mass because of the big frame and it didn't accelerate, but after we shortened the frame and loss mass, it accelerated much faster.  Newton's third law states that every action has an equal and opposite reaction. This is relevant to our car because when the trap went off and the wheels pulled the car forward, the equal reaction was that the car pulled the wheels backward.

      The two types of friction present were kinetic and static. We didn't have any problems with friction in fact, but we actually used friction to our advantage by putting balloons on the two rear wheels. Since the balloon material has more friction than the plastic CD's, this allowed for more traction in the rear. We only put balloons on the back because they were actually the only power behind the car, as the front wheels just spun on the axel.
      We took into account friction when accounting for how many wheels we should use, but we figured that using four wheels would be more stable. We chose to use CD's for all four wheels, because they were thin and therefore would have less friction when rolling. However, since the CD's were bigger than some other wheels in the class, they had a slower rotational velocity because of the size. The other groups with small wheels had a higher rotational velocity because they only had to cover such a small distance. 

      The conservation of energy states that energy can neither be created nor destroyed. When relating this to KE and PE, we could say that the car has all PE just before it takes off, and then it has all KE at about the middle when it is moving the fastest. As it slows down and eventually stops, it then converts all of it's KE back into PE. We could also find the efficiency of our car by measuring the workout/workin x 100. 
      Our lever arm was approximately 2 feet. The length of the lever arm definitely had a impact on the car's performance. At first w
e had a very long lever arm, but it was so long that it couldn't generate enough power to accelerate. As a result, we shortened the lever arm so that the force was less when it had to pull the entire car. This is because we know that torque=force x lever arm. However, because of the shorter lever arm, the power output of our car was less because the torque was less on the car. 
      Rotational inertia/velocity both played a part in the wheels of our car. Since our wheels were bigger than some other small wheels, they had a lower rotational velocity. They also had a higher tangential velocity because a point on the wheel had to rotate more than a smaller wheel would have to. Having smaller wheels would allow a higher rotational velocity and would have probably been more helpful. 
      We can't calculate the amount of work the spring does on the car because both the force and the distance (work=force x distance) have to be parallel, and in this case they are perpendicular. We can't find the amount of PE that was stored in the spring and the amount of KE the car used because work=∆KE/∆PE. We can't calculate the force the spring exerted on the car because there are many other factors that are decreasing the force on the car, such as friction, mass, etc.
      Our final design was extremely different than our original design. Initially, we were going to have a long frame and have records as the rear wheels. However, after the records broke, we decided to use CD's for the rear wheels as well. We then were stuck with a very long frame that was quite heavy and four smaller wheels. This is what prompted the thought to change our design. After 2 failed test runs, we realized that it was much too heavy, so our last hope was to cut the frame out and glue the ends back together. This surprisingly worked, and the car accelerated and even made it the 5m after an adjustment to the string.
      Similarly to what I said previously, the only major problem we had was that our first design was too heavy and didn't accelerate at all. Our first minor solution ideas were to shorten the lever arm and to increase the width of the rear axel, but after it still didn't accelerate again, we knew we had to make a more major change. Near the end of class, we decided to cut the frame out and glue the sides back together to reduce mass. This actually worked very well and is what saved us in the end.
      If we were to do this project again, I would definitely consider making my car as light as possible, as well as using smaller wheels. Making the car small in general seemed to work the best, as the fastest car in the classes was quite small. Also making sure the axels are stable and secure so that there is minimal wobbling when the car is rolling.

      

Unit 5 Reflection

      The first thing we learned about in this unit was work and power. The formula for work is force times distance and the formula for power is work/time. I found out that work and power are related because you must have work in order to find out the power. One of the most important things we learned about was that in order for there to be work, the force and distance must be parallel. If they are perpendicular, then there is no work done. We also needed to remember that when working with stair problems, we should use the vertical height as the distance. The units for work are joules and the units for power are watts (aka joule/second). We also talked about horsepower, and we learned that 1 horsepower is equal to 746 watts. So if we did 1600J of work in 2 seconds, then we would have made enough energy to make one horsepower. As you can see in this image, the vertical height it was is important when calculating the work.
      The next thing we learned about was kinetic and potential energy, as well as the relationship between work and both KE and PE. We found that work is equal to the change in KE, or movement. The formula for KE is 1/2mv^2. When solving problems that ask how much greater the distance will be when a car stops at two different speeds, it is important to remember that the velocity is squared. So if the car stopped at 5m/s, then at 10m/s, you could say that the velocity doubled so you would put in a 2 for the v. That would mean that the distance, work, and KE are all 4x as much, since 2^2 is 4. We also learned that PE is PE=mgh. When asked if something can be moving and have PE, I found that this is true. It's PE could be decreasing as it moves but it could still have some as it converts into KE. Also, ∆KE=∆PE.
In this animation, the ball has all PE at the top and no KE. In the middle, it has equal or almost equal KE and PE. When it hits the bottom, it has all KE and no PE.
      The conservation of energy states that energy can neither be created nor destroyed. When connecting this to what we just learned about KE and PE, we could say that the energy must be conserved at all times. One example we used was that if we threw a ball in the air with air resistance, would it return to it's starting position with the same, less, or more KE than it started with? Well, KE is basically speed, and air resistance slows things down, then the answer would be less KE. Another example we used and actually demonstrated in class was a pendulum, where the ball would start out with some PE and would return to it's starting position with slightly less PE each time. It would never return with more PE or KE or else it would violate the conservation of energy.
      The last thing we learned about is simple machines. A machine is used to reduce the force in which it takes to push or pull something. The first machine we learned about was an inclined plane. A few key equations we had to remember when working with machines was that work-in=work-out and f-in x d-in= f-out x d-out. YOU CAN NEVER PUT IN LESS WORK IN A MACHINE THAN YOU GET OUT. If you got more work out than you put in, the machine would violate the idea that machines can't be more than 100% efficient. To find the efficiency of a machine, you take the workout/work-in and then multiply it by 100 to get a percent. The main reason that machines work is because they increase the distance so that the force is less. An example would be if you were trying to load a 30N box into a 1 meter high truck by using a 3 meter long ramp. Both lifting the box straight up and using the ramp use the same amount of work, however the ramp increases the distance so that the force is less as you push it up. Another example we used was that when cars drive, they don't use all of the joules of work. The remaining joules get converted into heat, sound, etc. So when your engine is both loud and hot, you are wasting a lot of the work your car could be using to move your car.
      I found this unit somewhat challenging; the hardest thing for me was remembering all of the equations and how they relate to each other. Other than that, I feel that I did fairly well on the quizzes, and my groups podcast was both funny, informative, and clever. We all tried to make a rap that incorporated as many details as we could but still sound good at the same time. I also kept up with all of my homework which was very helpful because I never felt left behind. Overall, this was a fun unit to learn about and I enjoyed how it was taught and related to the real world.























   

Machine Resource

This video made by some other physics students which shows all 6 of the simple machines. Even though they aren't the best actors, they both use examples and explain how the machines help them move things easier, by using a greater distance which means having to use a lesser force. This is also helpful in understanding machines, because of how they explain it and show real life examples.

Work and Power Resource

This video is very helpful in explaining work, power, watts, and even more. It's use of examples and writing as the examples are moving is very helpful in understanding the material. It also has fun facts, I learned that the watt is named after a man named James Watt. How cool!