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Autos for Physicists

  1. Aug 28, 2007 #1
    I am interested in learning about how automobiles are designed from a physics/engineering perspective (i.e. what are the basic components in an auto and how do they work together to make the thing move?). I know embarassingly little about this topic. I can't seem to find a decent place to start. Does anyone have any suggestions?

    PS. This is intended to be bedside reading, so it can't be too dull and unengaging!
    Last edited: Aug 28, 2007
  2. jcsd
  3. Aug 29, 2007 #2


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    Hi, Euclid.
    There are a lot of different kinds of cars, built for a lot of different purposes.
    The foremost requirement is structural integrity. That, essentially, ensures that the thing won't be crushed like a used Kleenex if it hits something. Variations of that go from egg-crate with crumple zones, through steel full box frames up to full titanium or chrome-moly frames with intergral roll cages. There are a lot of approaches, each of which is intended to maximize the survival chance of someone inside.
    From the appearance perspective, it is based upon the target market. There's a huge difference, in principle, between what a soccer mom and a 16 year-old street-punk wants (and I am not by any means implying at any significant percentage of 16 year-olds are 'punks'). Then there's the old streeters like me. I found it incredible that the name of one of my favourite cars from slightly after they quit building really good ones has re-emerged as something that would fit all of us—the Dodge Magnum. Back when I was still in the scene, the Magnum XE came out, and I so wanted to buy one and stuff a hemi in it. It just had such great lines. Now, it's re-emerged as a mommy-mobile... with a hemi. Okay, it's a baby-hemi, but still...
  4. Aug 29, 2007 #3
    Hi Danger,
    Thanks for the response! Although I think the problem of death-prevention is really important and interesting, I am more interested in the inner workings of the machine. Perhaps I should start with engine design principles? Any suggestions?
  5. Aug 29, 2007 #4
    Hello Euclid,
    A viable approach may be to "track" the flow of energy throughout the vehicle. Energy is stored chemically in gasoline, and the chemical reaction of combustion within the engine causes a rapid expansion doing work in the pistons. The combustion gas is processed for removing NOx, particles, etc. before being exhausted. In some cars there are electronic systems capable of measuring parameters of air intake and exhaustion gas, and adjust the conditions in the engine accordingly.

    The work from the engine is transmitted via shafts and axes to the gearing. This transfer may be analysed through classical mechanics (rotational energy, moment of inertia, etc.). Also the gears themselves and the transmission to the wheels may be analysed thusly. Mind you that I'm no automechanics wiz, and I shall be the first to admit that the description of the system might be, and likely is, incomplete.

    Other aspects are the shock absorption system, and minimizing air drag through both the geometric design of the vehicle and through microscopic modification of the surface texture.

    The engineering aspect has two main points that I can think of: Safety, which was discussed by Danger (I am not the only one spotting the irony there, am I?), and energy efficiency, i.e. as much yield as necessary with as little fuel use as possible.

  6. Aug 29, 2007 #5


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    Nesk, how is it that you have over 30 posts, and obviously have a good grasp of things mechanical, and this is the first time that I've encountered you?
    Anyhow, that was a nice response. I never got around to stuff like aerodynamics, suspension, fuel economy, etc.. (Got side tracked by the thought of the Magnum and started day-dreaming. :redface:)
    As for the design principles, Euclid, they really are 'purpose-built'. I could try to elaborate upon that (and I will if nobody else does), but the guys that you should listen to about it are Brewnog, Stingray, Hypatia... Nesk...
    Last edited: Aug 29, 2007
  7. Aug 29, 2007 #6
    Thank you, Danger. I'm flattered. :redface:

    Saying that I have a good grasp of things mechanical might be a bit of an overstatement. If I peeked beneath a bonnet, I'd probably not be able to identify anything but the hole through which one adds oil, and that'd only be if it had "oil" written on it in very large bright letters. :smile:

    How is it that you haven't encountered me 'till now? I've spread those ~30 post over a few sections, so I guess my presence has not been so intensive as to attract much attention. :cool:
  8. Aug 29, 2007 #7


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    I don't think so; I usually have pretty good instincts about this sort of thing. Whether or not you have the hands-on experience and the particular knowledge of certain engines, drivelines, etc., you obviously have a very good 'feel' for the dynamics of the system as a whole. Your mind works in a good way; keep it up.
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