Is support force a true force ? it seems incompatibe with F=ma

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    F=ma Force Support
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SUMMARY

The discussion centers on the nature of the "support force" and its classification as a true force in the context of Newton's second law, F=ma. Participants argue that while the support force exerted by a table on a stationary box is real, it does not result in net acceleration, as the forces acting on the box (its weight and the support force) cancel each other out. The conversation also contrasts the support force with centrifugal force, clarifying that centrifugal force can be considered a true force in certain contexts, particularly when discussing reactive forces in a rotating frame of reference.

PREREQUISITES
  • Understanding of Newton's second law (F=ma)
  • Familiarity with the concepts of net force and acceleration
  • Knowledge of inertial and non-inertial reference frames
  • Basic grasp of reactive versus fictitious forces
NEXT STEPS
  • Research the implications of Newton's laws in static systems
  • Explore the differences between reactive centrifugal force and fictitious centrifugal force
  • Study the conditions under which forces are classified as "true" forces
  • Investigate the role of support forces in various physical systems
USEFUL FOR

Students of physics, educators explaining force concepts, and anyone interested in the foundational principles of mechanics and force classification.

  • #31
MrAnchovy said:
Yes. I am also saying that it is IMHO no less correct (and a lot more helpful) to refer to this as (reactive) centrifugal force rather than string tension than it is to refer to the force of the table on the box as normal or support force rather than intramolecular force.

Maybe. But it seems to me that the benefit of talking in terms of "normal force" is that it hides details that are (A) irrelevant and (B) too complicated to get into. We're abstracting away from the details of how normal forces arise, and just using the property that its a contact force and is directed perpendicular to the surface of an object. Similarly, "string tension" hides the details of intermolecular forces, keeping the important facts that its direction is tangent to the curve made by the string. In contrast, "reactive centrifugal force" doesn't seem to be making the analysis any simpler, it's just giving a name to one of the several forces involved in the problem.

But it's often a matter of opinion and taste whether it is worth-while to have special names for things.
 
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  • #32
WannabeNewton said:
The centrifugal "force" is a coordinate artifact

Not the way he's using it. Actually, that's another reason I don't like his terminology, is that it's hard to keep straight whether he's talking about the fictitious force, "centrifugal force", or the real force, "reactive centrifugal force".

The distinction, as I understand it, in the case of a mass swirling on a string, is that "centrifugal force" is a fictitious force, and acts on the mass, while "reactive centrifugal force" is a real force, and acts on the string. They are numerically equal, but they act on different objects.
 
  • #33
FWIW I spend a lot of my working life on the dynamics of rotating machines. I can live with the term "centrifugal force" though I prefer "centrifugal stress" which is both a real stress and self explanatory - i.e. the stress fiield caused by the rotation of the system.

On the other hand I have never (in 30 years in industry) heard anybody use the term "reactive centrifugal force", until a few recent threads in PF - and I don't see any merit in it.
 
  • #34
AlephZero said:
On the other hand I have never (in 30 years in industry) heard anybody use the term "reactive centrifugal force", until a few recent threads in PF - and I don't see any merit in it.
I've never heard the term outside of PF either (except for a wiki page) and I also see no merit in it.
 
  • #35
stevendaryl said:
The distinction, as I understand it, in the case of a mass swirling on a string, is that "centrifugal force" is a fictitious force, and acts on the mass, while "reactive centrifugal force" is a real force, and acts on the string. They are numerically equal, but they act on different objects.
Hmm, can't say I've ever heard of the "reactive centrifugal force". I'll read up on it thanks.

EDIT: I tried looking it up and I just found other forum links, a wiki link, and a facebook link (lol). Is there like some textbook this is discussed in? I couldn't find anything in Kleppner about it, which is the book I usually turn to, nor could I find anything in Taylor.
 
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  • #36
AlephZero said:
On the other hand I have never (in 30 years in industry) heard anybody use the term "reactive centrifugal force", until a few recent threads in PF - and I don't see any merit in it.

I agree; I had never heard it before until used here and I will stop using it (even reluctantly and in brackets) now.

AlephZero said:
FWIW I spend a lot of my working life on the dynamics of rotating machines. I can live with the term "centrifugal force" though I prefer "centrifugal stress" which is both a real stress and self explanatory - i.e. the stress fiield caused by the rotation of the system.

I can see some merit in "centrifugal stress" - but only if we replace "normal force" with "normal stress" too! And if we are going to stop using the word "force" for things that are forces, we should definitely stop using it for things that are not - so "centrifugal effect" is a much better term to be used in a rotating reference frame.

On a more serious note, what WOULD be better would be if those who have mastered the maths of non-inertial frames of reference (or think they have) did not proclaim with such puffed-up joy statements such as "centrifugal force doesn't exist" which causes confusion and doubt in minds that are beginning to relate equations of motion to their everyday experience - this is exactly what turns intelligent, curious people away from science.
 
  • #37
On a more serious note, what WOULD be better would be if those who have mastered the maths of non-inertial frames of reference (or think they have) did not proclaim with such puffed-up joy statements such as "centrifugal force doesn't exist" which causes confusion and doubt in minds that are beginning to relate equations of motion to their everyday experience - this is exactly what turns intelligent, curious people away from science.
Would it not be even better if we all stuck to standard textbook terms and explanations. There is no shortage of expert knowledge outside PF.
 
  • #38
WannabeNewton said:
Hmm, can't say I've ever heard of the "reactive centrifugal force". I'll read up on it thanks.

EDIT: I tried looking it up and I just found other forum links, a wiki link, and a facebook link (lol). Is there like some textbook this is discussed in? I couldn't find anything in Kleppner about it, which is the book I usually turn to, nor could I find anything in Taylor.

DaleSpam posted some books:
https://www.physicsforums.com/showthread.php?p=4259305&highlight=google#post4259305

The reason why this is not discussed much, is that there is not much to discuss. It is not some elaborate concept, just a naming convention for the 3rd Law reaction to some centripetal force.
 
  • #39
MrAnchovy said:
On a more serious note, what WOULD be better would be if those who have mastered the maths of non-inertial frames of reference (or think they have) did not proclaim with such puffed-up joy statements such as "centrifugal force doesn't exist" which causes confusion and doubt in minds that are beginning to relate equations of motion to their everyday experience - this is exactly what turns intelligent, curious people away from science.

I think that's baloney. Someone is going to drop out of trying to learn science because someone tells them that centrifugal force doesn't exist?
 
  • #40
stevendaryl said:
I think that's baloney. Someone is going to drop out of trying to learn science because someone tells them that centrifugal force doesn't exist?


This is an opinion, not a scientific fact.
 
  • #41
This post should end now. 30+ posts resulting from a basic misunderstanding of some very basic physics.
I think someone has already pointed out that the explanation was given in post 2.
We have now degenerated into non specific opinions which are not part of the recognised physics literature. None of the references above are available from my book store.
 
  • #42
A.T. said:
DaleSpam posted some books:
https://www.physicsforums.com/showthread.php?p=4259305&highlight=google#post4259305

The reason why this is not discussed much, is that there is not much to discuss. It is not some elaborate concept, just a naming convention for the 3rd Law reaction to some centripetal force.
Thanks A.T.! I never knew it had a name. That's interesting :-p Not a fan of the terminology though
 

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