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Is torque a necessary defenition?

  1. Feb 16, 2007 #1
    im going mad, is torque necessary? is there no more basic explanation using newton's laws to explain why two tangent and equal forces(which are in opposite direction along the circle) even values, with different levers would rotate in the direction of the force with the bigger level is pointing at?

    i know that if the force with the smaller lever would make it rotate it would violate the conservation of energy, since if the body moved for a certain angle, then the work of the small levered force is smaller than the work of the big levered force(same forces, different lengths along the parameter), therefor the body is supposed to slow down, yet it accelerated up... which is a contradiction to the conservation of energy.

    so can torque phenomenons be explained by other means?
  2. jcsd
  3. Feb 16, 2007 #2
    Can you reword your questions more clearly please? I dont really understand what your asking. :confused:
  4. Feb 16, 2007 #3


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    Hint: get a good textbook and read.
  5. Feb 16, 2007 #4
    torque is really just a useful quantity to define, as it can be frustrating to work through the math related to conservation of energy in any given torque problem, if you want I can help walk you through how to derive torque from first principles, and most importantly why its equal to the quantity F*r (for a basic definition)

    first take a look at what units torque is measured in.
  6. Feb 16, 2007 #5
    cool, its good to know that moment is not something as basic as force...
    and ill think ill try to develop the equations myself(those using torque), shouldnt be to hard i think...

    bah, its quite hard to understand physics without having an organized book, my head is a mass even with the little i know..
  7. Feb 16, 2007 #6
    hmm if your not using a book I'm afraid you won't be able to get very far

    "the internet is a mile wide, and an inch deep"

  8. Feb 16, 2007 #7
    very true, but in some way it forces me to think more, since it "hides" a lot of information.

    i do like being fundamental when learning, though im not buying a book on mechanics since ill have one in a year when ill do a course in the open university(the books are a part of the course's payment), so it will be a waste to buy a big set of books.
    though now i just started reading feynman's lectures on physics, though it aint much fundamental i guess...
  9. Feb 16, 2007 #8


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    Tuvia, you must have books.

    Mods , I'd like to lend Tuvia a couple of books on classical mechanics.
    I don't know what the rules say, but you may give him my email address.

  10. Feb 16, 2007 #9
    i am very unsure if i understood you... are you talking about ebook(pdf file or something?)
  11. Feb 17, 2007 #10


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    Since I made that post, I had a look for the books in question ( Schaum "Lagrangian Mechanics" and another called "Classical Mechanics") and I can't find them. So my offer is withdrawn, sorry. They may not have been what you need in any case.

  12. Feb 17, 2007 #11
    if you have a problem involving radial symmetry, it will be only natural to have torques. For instance, the central force problem. by going radial, you reduces one degree of freedom by noticing that net torque is zero. If you brake the radial force into x,y components, you can still solve the problem but it will be ugly and inelegant.

    things become even more complicated when you study rigid body motion. How can you consider x,y components of the intermolecular forces for each individual molecules? If you go to radial symmetry, you can assume that all internal forces are central and that saves a ton of trouble.

    And as Radou said, get a good textbook and you will see how the physics is simplified in some problems by considering torque.
    Last edited: Feb 17, 2007
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