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Thread: Friendly reminder...nearly all torque values are in foot pounds...

  1. #71
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    Quote Originally Posted by Raven Armament View Post
    I'm not trying to debate semantics, just trying to use correct terms for units.

    I was under the impression that kinetic energy is measured in foot-pounds and torque was measured in pound-feet and pound-inches.

    Does it differ between industries? Vehicle engine torque is expressed in lb-ft.

    I know energy is not torque.
    Mathematically, torque is a vector where energy is a scalar. Energy is a real phenomenon which exists independently of mechanical engineers. Torque is an invented quantity which describes two forces parallel but in opposite directions and separated by a distance. Torque doesn't really exist, what it really is is two equal and opposite forces separated by a distance.
    Last edited by Suwannee Tim; 12-16-11 at 20:15.

  2. #72
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    Quote Originally Posted by Raven Armament View Post
    I'm not trying to debate semantics, just trying to use correct terms for units.

    I was under the impression that kinetic energy is measured in foot-pounds and torque was measured in pound-feet and pound-inches.

    Does it differ between industries? Vehicle engine torque is expressed in lb-ft.

    I know energy is not torque.
    energy has the same units as torque. those units are

    (mass) (length)^2
    --------------------
    (time)^2

    typical unit for mass = kilograms, the english units equivalent would be (pounds)/(acceleration of gravity) because pounds is a force.

    typical units of length = meters, feet

    typical unit for time = seconds

    typical units for energy = joule, btu, calorie...

    joules (the SI unit for energy)

    a joule is [(1 kilogram)(meters)^2]/[(seconds)^2]

    if you take a typical equation for energy like kinetic energy

    (1/2)(mass)[(velocity)^2] you can see that

    mass is measured in kilograms and velocity is measured in meters/second.

    once you spell it all out you get the definition for joule above. [(1 kilogram)(meters)^2]/[(seconds)^2]


    sidebar:
    btus (the english unit for energy). i can't even begin to explain what a btu is because it's an antiquated piece of crap that is largely based on empirical values.


    torque is force at a distance and in the SI units it comes out as

    T = (Force)(length)

    F = (mass)(acceleration).

    acceleration comes in units of meters/(seconds^2)

    length comes in units of meters

    when you spell it out you get

    T = kilograms [meters/(seconds^2)] [meters]

    which is the same thing as

    [(1 kilogram)(meters)^2]/[(seconds)^2]

    just arranged slightly differently.



    Quote Originally Posted by GTifosi View Post
    No difference between industries as the terms are mathematical formula generated, not Ford or Colt or Fastenal. Math is math no matter who crunches the numbers.

    Joe everyguy is just sorta subliminally conditioned to the ft/lb thing because that's what he hears the most, or at least at a vastly more frequent amount of times unless he happens to work in a specific industry or other.

    How many times a day do you hear 'ft/lbs of torque'?
    Likely as many times as you see read or hear a car, truck, motorcycle, electric motor, etc., etc. advertisement along with any sort of powered motorsport announcing because they are pimping power as a feature.

    But you almost never hear about how a lug nut or cylinder head should be affixed at so many lb/ft for proper anchorage.

    IOW, you are correct, its just one of those broad misunderstandings.
    Like lemming supposedly running off cliffs en'masse or that duct tape can fix anything.
    i would say depending on your industry, the scale of the thing being measured and the country etc you will refer to torque and energy and even power units in different ways. if you work in a powerplant you may use btus. if you work in a lab in the united states that has a lot of international traffic, you would use joules. if you are in the automotive world in japan you may use "newtons meters" instead of foot pounds.

    Quote Originally Posted by Suwannee Tim View Post
    Mathematically, torque is a vector where energy is a scalar. Energy is a real phenomenon which exists independently of mechanical engineers. Torque is an invented quantity which describes two forces parallel but in opposite directions and separated by a distance. Torque doesn't really exist, what it really is is force and distance.
    units of measure are convenient ways to assemble the fundamental units so you can cross out stuff easily in math and use special coordinate systems to describe things in a relevant/sensible manner. they're all concepts. even energy, it's just a lot easier to write joule, J, KE, E_k, or say energy instead of [(1 kilogram)(meters)^2]/[(seconds)^2] every single time you want to describe that specific phenomenon.
    Last edited by trinydex; 12-16-11 at 20:52.

  3. #73
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    Quote Originally Posted by trinydex View Post
    energy has the same units as torque. those units are <snip>.

    for those playing along at home, Pound/ Feet is the correct nomenclature for torque as we're talking about 40 pounds acting on one foot not 40 feet acting on one pound. That said, the point of communication is to be understood so as long as we all understand each other there isn't much point to the discussion.

  4. #74
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    Quote Originally Posted by Tweak View Post
    for those playing along at home, Pound/ Feet is the correct nomenclature for torque as we're talking about 40 pounds acting on one foot not 40 feet acting on one pound. That said, the point of communication is to be understood so as long as we all understand each other there isn't much point to the discussion.
    To throw my hat into the semantic ring...those are equal torque values. Also, just a little nitpick but a lot of people tend to use a division sign between lb and ft (in whatever order you like) and that is not the proper terminology if we are talking about torque or energy...it doesn't mean the same thing.

  5. #75
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    The most common by far terminology for torque is foot pounds, inch pounds, newton meters or such. I can't say that pound feet is wrong but it is not common. Pound/feet is wrong, this is weight per unit length, not torque. Reminds me of the late great P.O. Aclkey who insisted on reporting velocities in foot seconds not feet per second. He had some kind of rationale which I can not remember.

  6. #76
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    This is turning into another dead horse. Why is that? It looks like people are fighting over the pronunciation of the word POTATO.



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  7. #77
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    Po tay toe?
    Poh tah toe?

    So which is it?

    Back to the topic, most very good mechanics etc, come very very close to actual torque specs, but it does get more difficult to hit those specs when they get higher in bushels of potatoes torque numbers. For the receiver extension, hitting that +/- Potato spec is not too difficult for experienced builders. Also there is less worry with heating and cooling.

    I tend to be more specific with barrel nuts as the dissimilar metals, heating and cooling and movements of metals and I use a torque wrench in various methods depending on the nut. USGI type nut, set at initial 30-35 potatoes and then rotate to next gas tube slot, provided that slot is not more than half way away as that will usually make your potato torque over spec. If this is the case then you need to do a bit more work.

    However say on a DD barrel nut where there is no gas tube relation, I tend to use a torque wrench set in the 60-65 potato range . I also tend to "work" my threads on barrel nuts also, but if I really get into my explanation of why, how and the reason that I feel it is a good thing, it might continue into another 10 pages of discussing TOMATOES.


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    mea culpa I meant with pounds before feet instead of feet before pounds. Since I thought we all knew what we were talking about I put the slash in there as shorthand instead of typing it all out. So it should have been pound-feet which still is not symbolically correct using some peoples logic as it should be force times distance not force minus distance.

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    Quote Originally Posted by Tweak View Post
    for those playing along at home, Pound/ Feet is the correct nomenclature for torque as we're talking about 40 pounds acting on one foot not 40 feet acting on one pound. That said, the point of communication is to be understood so as long as we all understand each other there isn't much point to the discussion.
    i hate to be the technicality person, but there is no / or division sign. as you can see from the math above it is feet*pounds or pounds*feet.

    you will notice the british frequently use the the phrase pound feet of torque and the americans frequently use foot pounds of torque.

    one pound acting at 40 feet away from a fulcrum is the same amount of rotational force as 40 pounds acting at 1 foot away from a fulcrum.

    Quote Originally Posted by Tweak View Post
    mea culpa I meant with pounds before feet instead of feet before pounds. Since I thought we all knew what we were talking about I put the slash in there as shorthand instead of typing it all out. So it should have been pound-feet which still is not symbolically correct using some peoples logic as it should be force times distance not force minus distance.
    to be extra clear, there is no symbol between pound and feet when pronouncing the units. the units are multiplied and if you were really daft you could say pound times feet of torque, but no one would ever do such a thing.
    Last edited by trinydex; 12-21-11 at 21:56.

  10. #80
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    When I do anything with an AR I use a torque wrench and do a careful job of tightening to spec. I'm very inexperienced compared to someone like IG and I figure I'm better off knowing my limitations and playing it safe. I have no doubt that someone like IG can tighten by feel and get pretty close but I don't trust myself to do that.

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