5 Discussion and Conclusions
According to the graph above, there is two parts to how the car accelerates. In the first 1.5s, the car releases its stored elastic potential energy. During this part, the car accelerates and the elastic potential energy of the spring is then converted into other forms of energy like kinetic and heat energy.
After 1.5s, all the elastic potential energy of the spring is converted into other forms of energy. Majority of the energy is converted to kinetic energy. The total kinetic energy of the car can be calculated by taking the work done of the car and minusing the friction of the car.
To calculate work done:
Force x Distance over which it acts
= Mass x acceleration x (Total Distance - Distance travelled during power stroke)
This work done, can also be calculated by finding the Potential Energy of the spring
Work Done=Potential Energy
Potential Energy=1/2kx ( ½xspring constantxamount of (spring stretched)
This work done is also the work done needed to wind up the spring.
Thus: WorkDone(to stretch spring/EPE) - Friction = Kinetic Energy
Conclusion: The elastic potential energy of the car, and it's friction eventually determines the maximum kinetic energy of the car.
This means that the factors affecting the maximum KE is:
1. Mass( KE=½ x Mass x Velocity^2)
2. Length of String/Rod (½ x spring constant x Distance ^2)
3.Tension of Spring (½ x spring constant x Distance ^2)
4. Acceleration of car ( WorkDone(by friction)= Mass x Acceleration x Distance)
5.1 Key findings
1) The tension of the spring of the mousetrap is the thrust for the car, allowing the car to travel forward. The greater the tension in the mousetrap, the more energy it can convert to kinetic energy, causing the car to move forward more.
2) The type of base placed underneath the mouse trap must be thick and strong as the force exerted when the car is released might damage the base. This would affect the performance of the car.
3) The type of wheels used, the diameter of the wheels and etc. affect the car’s performance vastly. A large drive wheel covers more linear distance for each rotation as compared to a smaller wheel.
4) The car should be as heavy as possible, the more mass the more inertia. With more inertia, the car will move further after the power stroke of the car has ended..
5) The length of the string (power stroke) and the length of the lever extension has a great impact on the distance travelled by the car.
6) It is best to build a slow moving distance car as a slow car is more energy efficient than a car travelling at a higher speed as it will have more air resistance.
7) The traction of the wheels should be increased to increase acceleration.
5.2 Comparisons with other designs based on research
Our design looks looks flashy and colourful due to the balloons we had placed on our wheels. However the materials were mostly what we could find easily and we only bought the styrofoam wheels, the rest we found it lying around the house. Compared to other designs, we had the smallest and easiest car to build as we used the mousetrap as the base itself and did not require other materials as the body, such as wood or anything. I think our car made use of whatever materials we had existing already and just kept improvising till the design produced the best results. Overall we were not very ambitious to go and copy the other more complicated designs of the mousetrap car that we found online as we were not also very sure whether it would have worked well, so we just stuck to our feeling and built an easy car that could work well by improving and improvising along the way.
5.3 Evaluation of engineering goals
Develop a MouseTrap Car with the following specifications:
Uses only the MouseTrap provided as the only energy source
Rating: 9. Most of the energy is powered by the mousetrap. However, there is a little elastic potential energy stored in the stretched fishing string.
Has a maximum length of 30 cm, width of 10 cm, and a height of 10 cm
Rating: 10. All length, width and height adheres strictly to the restrictions
Can travel a minimum distance of 5 meters carrying an egg (the egg will be provided by the teacher)
Rating 10. Our car can travel 8 or more metres and there is an egg holder to carry the egg.
All time-lines have to be adhered
Rating 10. All deadlines have been strictly adhered to.
5.4 Areas for improvement
1) Our car was not able to move in a straight line. We could have spent more time working on how to prevent it from moving to the right, but then we would have to almost redo the whole car, so we just decided to place it slightly to the left during the testings.
2) We could have thought about how to place the egg on the car. However, we were more concerned about whether the car would be able to travel for 8m. Hence we forgot all about the egg in the end, and did a last minute egg holder by using masking tape to hold a ruler to the body of the MTC, with a egg carton on top.
3) We did not research a lot on mousetrap cars and the scientific best ways to build it. We just started to build ordinary easy mousetrap cars and hence had many failures at the start. But we kept improving our prototypes and testing it out, finding the problems and tweaking parts to make the car move better and further. It would have saved us time if we had read up more about the building of a mousetrap car first before building it based on our prior knowledge.
5.5 Practical Applications
1) Children can play with this car with adult supervision and safety precautions would be taken (Spikes on the mousetrap car would be sealed to prevent the children from injuring themselves) as it does not require electricity or batteries. It is very eco-friendly.
2) A stronger elastic spring may be used in the future. This may be implemented in cars sometime in the future where you may only need to wind up the spring once using tools to help you. The wound up spring would also enable the car to move quite a distance before having to wind up again.
5.6 Areas for further study
1) We can find out if there are better materials other than mousetrap that has better elastic potential energy.
2) We can test the cars on different types of surfaces to see which surface is suitable to be used for roads.
3) We can also see how the use of other types of energy such as kinetic energy and solar energy to see how it affects the distance travelled by the car.