Rocket Man
Van Car Lab Report
Engineering Objective:
My objective was to build a car that could be powered by an Estes D11 model rocket engine. A secondary objective was to have my car move in a relatively straight direction. A tertiary goal was to have my car become sentient so it could overtake society as we know it; however, since gerbil power was disallowed and the Geneva Convention was in effect, this became impossible.
Design Considerations:
My design was considerably limited by two factors: available time and materials. I did not have much time to work on the car, due to several factors (the research project being one of the main ones). I was also unable to spend much money on my car; beyond the wood for the body, every other part of the car was something that I already owned. The body was made of wood because it was an affordable material, durable, and typically tends to work well for projects like this.
I am not the slightest bit mechanically inclined, so I felt uncomfortable with making drastic changes to the body of my car. The only work that I did on it was to shape the front end of the car and to make it slope upwards; this was to add a modicum of aerodynamics to the car as well as it make it so that it was not just a two by eight with wheels.
My primary concern with the wheels was to have them relatively straight and to turn easily. The car’s axles were made of K’NEX pieces; I chose to use these as I already had them and because they roll relatively smoothly. The wheels were locked into position on the axles, which rotated along with the wheels. The axle assembly was attached to a second piece, which was then screwed onto the underside of the car.
With that, I believed that my car was finished. It had wheels which were nice and round, and it rolled smoothly and in a (somewhat) straight line. Little did I know how wrong I would be…
Materials:
The materials used in the construction of my car were as follows:
This may be the least impressive materials list I’ve ever written.
Diagram:
The diagram is attached via the stapled sheet on the back of this report. To be completely technical, I guess it would be attached via a staple. I have no idea what “EL” is or how to measure it, and I’ve given up entirely on finding the center of mass of my car. I can’t disassemble it to mass all of its components at this point, so I don’t think I can find that. Besides…I’m hoping that I’ll get some kind of credit simply for turning this mess in.
Data:
I don’t have any actual data here, as our setup did not allow recording the acceleration, speed, distance, or…well, anything for the cars. It would have helped greatly if stupid safety precautions didn’t require us to stand back and hide near cover while launching the cars. Measuring the distance the car had traveled would have been possible, but we did not have any tools to do this with. I did not have time either, for that matter, as I had to go to my next class. On the plus side, I know that I’m not the only one without this information. I can’t fail for not having what no one else in the class has, can I?
Observations:
The car’s launch was…well, interesting. It was fired from the leftmost launching thingy, and it veered off into the right and smashed quite spectacularly into the snow bank. It flipped upside down, and it lost three of its four wheels in the process. This is probably proof that you should not use axles that can be snapped apart with a minimal amount of force; however, it is worth noting that the wheels were not lost until the car hit the snow banks and flipped.
Data Analysis, Interpretation, and Error:
To be honest, I’m not sure what to do with the data analysis, or even what I should be finding. I have avoided greater obstacles, though, so it’s time to try this anyway.
The first step is probably recording the known data. My car weighed 800 grams exactly. The rolling resistance was 45 grams. And the impulse of the engine, as reported by Kevin (who had best hope he’s right), is 19.5 Ns. That much is certain.
The impulse here is known, and I can use that to figure out the velocity of my car. The first step would be to convert the weight of my car to Newtons. This is simple enough; I just have to multiply mass by gravity.
Newtons = Mass x Acceleration = .800 kg x 9.81 m/s2 = 7.85 N
After that, finding velocity is a simple division problem. Impulse is equal to mass times velocity, so velocity should equal impulse divided by mass. For some reason, I read “mass” as “nuts” while proofreading, making the sentence comically nonsensical.
Velocity = Impulse / Newtons = 19.5 Ns / 7.85 N = 2.48 m/s
In theory, the car should have reached a velocity of 2.35 meters per second. In an idealized situation, this would be the maximum velocity that my car would reach. However, this isn’t an ideal situation. I’ve got to deal with the real world, and fun things like friction and drag forces.
I do not have my car’s acceleration, time, or any kind of frictional forces between the car and the ground recorded. It was not possible. I do, however, have the rolling resistance, the amount of force that it took for my car to begin rolling. This was 45 grams. Since resistance would increase the amount of force that it takes for a car to move (and decrease its velocity), I can find the theoretical, non-idealized velocity by adding the 45 grams to my car’s mass. The car’s actual weight in Newtons, then, is:
Newtons = (Mass + Resistance) x Acceleration = (.800 kg + .045 kg) x 9.81 m/s2 = 8.29 N
With this figure found, I can calculate the theoretical, non-idealized velocity of my car.
Velocity = Impulse / Newtons = 19.5 Ns / 8.29 N = 2.35 m/s
Even so, these numbers aren’t right. The car had to contend with things like an uneven sidewalk, wind, and snow that weren’t included in my calculations. My numbers are essentially meaningless, but they’ll work here.
The most obvious source of error is the car itself. A two by eight with wheels attached isn’t exactly the most aerodynamic (or well-engineered) example of a car. Having spent more time or effort on the car would have helped greatly. A better body would have been nice; a piece of wood with one cut in it was still better than what most of the other cars used, but it’s not exactly worthy of rocket science, which is what this lab was. Kind of. Also, using some kind of axles that don’t fall apart when they hit snow might be a good idea. The biggest issue I had with the axles (beyond that) was the fact that they slid from side to side in their mounts; finding a way to remove that sliding – and any accidental turns that would result from it – would have definitely helped to improve its performance.
Beyond that, I can blame a lot of things for my car’s failure to perform. The sidewalk and wind both impeded my car’s performance, producing resistance which is BAD. I also had to contend with my car smashing into the snow, which was also a BAD thing. Mine was launched at the same time as Matt Tse’s car was; it is entirely possible that launching the cars together could have had an adverse, or BAD, effect on mine. Swando’s elephants are a reason for error as well; they distracted me while I was writing this paper, which is never a good thing. Also, Sarah told me to mention marmosets. So I will, as they distracted me as well.
Conclusion:
My car failed to move in anything resembling a straight line, and collapsed upon impact into snow (which isn’t exactly a dense material). However, everyone else had the same thing happen to their car, so I consider this a roaring success. Also, the only reason why Devin’s car worked is that he injected it with steroids prior to launching it. I suggest a Senate inquiry followed by thousands of dollars of fines for this injustice.