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Friction is a Scalar

  1. Mar 28, 2015 #1
    In examining the work energy theorem on vector fields, I have concluded that friction must be a scalar field with a negative value. This is because one must integrate the line integral with respect to ds instead of the function dotted with dr. Am I correct in my understanding or am I missing something?
     
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  3. Mar 29, 2015 #2

    Vanadium 50

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    "Friction" is a phenomenon, not a quantity So what you wrote cannot be what you mean.
     
  4. Mar 29, 2015 #3
    All physical Phenomena are quantities
     
    Last edited by a moderator: Mar 29, 2015
  5. Mar 29, 2015 #4

    robphy

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    Is friction dependent on location alone (as might be expected for a scalar field)?
    If it did, wouldn't it be associated with a conservative field?
     
  6. Mar 29, 2015 #5

    Vanadium 50

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    Nonsense. "Motion" is not a quantity, but "velocity" is. "Space" is not a quantity, but "length" and "volume" are.

    You started this thread with a title that is incorrect, and in message 3, your entire message was an incorrect statement. Making incorrect statements hoping that someone will correct you is a frustrating and inefficient way to learn.
     
  7. Mar 31, 2015 #6
    I think I understand. Is there a unit vector which can be used to signify that friction is opposite to the direction of motion?
     
  8. Mar 31, 2015 #7
    Now I see my ignorance. My assumption was that the scalar form of friction was the Vector form of friction. I realize now that friction needs to be multiplied by the unit tangent vector. Thanks for correcting me.
     
  9. Mar 31, 2015 #8
    There is "friction", a phenomenon, and there is the "friction force". The first is neither vector nor scalar. The second is a vector, as any type of force.
    Same as "gravity" is a phenomenon and the weight or "force of gravity" is a force. People (especially students) tend to use "gravity" when they mean the force of attraction.
    This is OK in general but it may create confusion sometimes.

    Multiplying the friction by a unit vector (or by anything else) is not a valid operation.
    You can multiply the magnitude of the friction force by a unit vector, if you wish. Indeed the friction force is tangent to the surfaces in contact.

    And I think I understand (maybe) your problem.
    If you look at the equation
    Ff=μN, it makes sense for the magnitudes of the forces but not in vector form. The friction force is not parallel to the normal force.
     
  10. Mar 31, 2015 #9
    yes but the normal force in this situation is not a vector in this sense but simply a coefficient.
     
  11. Mar 31, 2015 #10

    Vanadium 50

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    No, the normal force is a force. And force is a vector.
     
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