Confirming if Friction is a Scalar: Examining the Work Energy Theorem

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    Friction Scalar
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Discussion Overview

The discussion centers on the nature of friction in the context of the work-energy theorem, specifically whether friction is a scalar or vector quantity. Participants explore the definitions and implications of friction as a phenomenon versus the friction force, examining related concepts in physics such as conservative fields and the role of unit vectors.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant asserts that friction must be a scalar field with a negative value, based on the integration of line integrals.
  • Another participant challenges the initial claim by stating that "friction" is a phenomenon and not a quantity, suggesting a misunderstanding of terms.
  • Some participants argue that all physical phenomena can be considered quantities, while others clarify that terms like "motion" and "space" are not quantities, but their respective measures (like "velocity" and "length") are.
  • A question is raised about whether friction is dependent on location, which could imply it is a scalar field, and whether it is associated with conservative fields.
  • One participant expresses confusion about the relationship between scalar and vector forms of friction, later acknowledging the need to multiply friction by a unit tangent vector.
  • Clarifications are made regarding the distinction between "friction" as a phenomenon and "friction force" as a vector quantity, with an analogy drawn to gravity and the force of gravity.
  • Participants discuss the equation Ff=μN, noting that while it makes sense for magnitudes, it does not hold in vector form due to the directional nature of forces.
  • There is a disagreement about the classification of the normal force, with one participant asserting it is a vector and another suggesting it is merely a coefficient in this context.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether friction is a scalar or vector quantity, with multiple competing views and ongoing debate about the definitions and implications of friction and related forces.

Contextual Notes

There are unresolved definitions and assumptions regarding the nature of friction and its representation in physics, particularly in distinguishing between phenomena and their corresponding forces. The discussion also highlights potential confusion arising from terminology used in physics.

Timothy S
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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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"Friction" is a phenomenon, not a quantity So what you wrote cannot be what you mean.
 
All physical Phenomena are quantities
 
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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?
 
Timothy S said:
All physical Phenomena are quantities

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.
 
I think I understand. Is there a unit vector which can be used to signify that friction is opposite to the direction of motion?
 
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.
 
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.
 
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yes but the normal force in this situation is not a vector in this sense but simply a coefficient.
 
  • #10
No, the normal force is a force. And force is a vector.
 

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