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A doubt about Mechanical Engineering problems and exercises

  1. Nov 4, 2016 #1
    Is it true that some mechanical systems( or machines or mechanisms) of problems and exercises of Mechanical Engineering books(engineering dynamics, mechanics of materials, fluid dynamics...) are invented ? That is, they don't exist in real life, they are created only for a particular problem or exercise. Or, are all the problems formulated from a real mechanical system( or machine or mechanism) ?
     
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  3. Nov 4, 2016 #2

    boneh3ad

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    Pick any scientific field and your above statement is still true: some problems and examples are invented purely for the purpose of illustration of a concept. They are generally inspired in some fashion by real-world problems, but oftentimes are simplified so that they can be solved more easily to illustrate the topic being taught.
     
  4. Nov 4, 2016 #3

    phinds

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    Textbook problems are almost always considered to use ideal components and therefore are only approximations of real-world situations.

    What difference does it make? The point is to use ideal cases to learn the basics so that later you can learn more details. Do you expect to learn to run without knowing how to walk?

    And just FYI, you don't have a doubt, you have a question:

    http://www.physicsforums.com/showthread.php?t=607274
     
  5. Nov 4, 2016 #4

    Bystander

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    Translation software has "doubts."
     
  6. Nov 4, 2016 #5

    phinds

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    But more to the point, it is taught incorrectly in Indian schools. See the link I provided.
     
  7. Nov 4, 2016 #6

    Bystander

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    I had noticed that, but disregarded it as biased sampling on my part and blamed the translation software.
     
  8. Nov 4, 2016 #7

    boneh3ad

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    I am not sure you can really say it is taught incorrectly in Indian schools. India is the largest English-speaking population on the planet, so I only think it fair to instead consider that it essentially represents a different dialect and saying "doubt" instead of "question" is not any more wrong than saying "cookie" instead of "biscuit".
     
  9. Nov 4, 2016 #8

    phinds

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    You are right of course. What I SHOULD have said is that it is taught in the Indian schools in a way that is perceived as wrong in American and British version of English, which is primarily what this forum is in.
     
  10. Nov 4, 2016 #9

    boneh3ad

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    That's fair. I originally got very confused at this translation on these forums until a while back when I had an Indian coworker who always used "doubts" and then it all clicked in my mind.
     
  11. Nov 4, 2016 #10

    Randy Beikmann

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    For the OP, I agree that realistic applications of physics are more interesting, but don't underestimate the value of problems that are a little "contrived." There are many simple problems that isolate a concept better than a more realistic one could - once you learn it very well, you can combine it with other concepts. Atwood's machine is something that I can't imagine seeing in real life, but it was very instructional in illustrating straight line and rotational dynamics together.
     
  12. Nov 5, 2016 #11
    I'm not talking about approximations of real situations or ideal machines modeled from real machines(Atwood's machine has real life applications, right ?). What I'm asking is if you can actually invent a mechanical system(or machine or mechanism) from nothing just for the problem or exercise.
     
  13. Nov 5, 2016 #12

    phinds

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    Well, of course you could, but it's still true that to make a useful pedagogical example, you would want to keep it simple. What's the point of your question, anyway?
     
  14. Nov 5, 2016 #13

    Randy Beikmann

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    I consider Atwood's machine a demonstration setup, but I suppose it might have a real application. I don't think I've ever seen one. It really was, as you say, invented just for an exercise.
     
  15. Nov 6, 2016 #14

    boneh3ad

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    The counterweights on hung sash windows come to mind. Although the actual Atwood machine was just invented to demonstrate the physics involved.
     
  16. Nov 6, 2016 #15

    Randy Beikmann

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    A very good point! I do remember those.
     
  17. Nov 7, 2016 #16

    CWatters

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    Why not?

    If you can invent mechanical systems to solve real problems why cant you do the same for pretend or exam question problems?
     
  18. Nov 9, 2016 #17
    The point is: I'd like to know how do the authors of Mechanical Engineering books(books of engineering dynamics, mechanics of materials, fluid mechanics...) and some university professors of Mechanical Engineering formulate those beautiful problems and exercises ? Do I need a PhD to formulate such problems ? Do I have to be working in the industry to see how mechanical engineering principles are applied in real situations to create the problems ? And what background do the professors have that makes them able to create such problems and exercises ? Could someone give me a detailed explanation ? PS: Asking here again as my new post was deleted.
     
  19. Nov 10, 2016 #18

    CWatters

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    When you solve an exam problem the first step is to extract the mathematical/physical problem from the problem text. Part of the examiners job is to do the reverse. I'm not sure it's as difficult as you think it is. Many problems are also variants of past problems.

    Personally I find the best problems are ones that combine different aspects of physics or problems that appear to belong to one branch of physics when actually the solution comes from another branch. There was one like that on this forum recently. It went something like.. a beam of light is shone through a prism and is bent by an angle (α) .. how much lighter does the prism get? You start off thinking it's about refraction and end up with Newtons laws.
     
  20. Nov 11, 2016 #19
    They are by and large roused in some design by genuine issues, yet frequently are rearranged with the goal that they can be explained all the more effectively to outline the point being educated.
     
  21. Nov 11, 2016 #20

    Randy Beikmann

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    You may have to really search/think hard, but you can find examples that are both simple and real. The hardest part of writing my book, since it not required for a class, was to make basic kinematics (the easy part) interesting. I ended up using examples showing how better braking reduces lap times in a road race, and how barely driving into the starting line beam (staging shallow) can reduce your elapsed time in a drag race.

    So I think it's more important to be familiar with many activities involving physics applications, and be able to identify simple ones, than it is to have an advanced degree.
     
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