Talk:Centripetal force

The result of the changing acceleration is surely the centrifugal force for which an equal and opposite centripetal force is required to constrain the circular motion. Rjstott

That's nonsense. Centrifugal force is an imaginary force that appears if you are in a rotating frame of reference. Centripetal force is the force that causes a motion to be circular, producing an acceleration that correspond to a change in the direction of the velocity. --AN

There's nothing imaginary about two opposing forces being equal and opposite. I agree that one is a result of the mass acceleration equation.Rjstott

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There is no "equal and opposite force required to constrain the circular motion".

The force equation is F=m a,

In the case of circular motion a=-v^2/r^2r, and F=-m v^2/r^2r. F points inside, and its nature depends on the problem, in the case of a satellite, F = G m M/R^2. Where is the "centrifugal force" in the equations?

There is also the reaction to F, but that acts on another body that depends on the problem, in the case of the satellite, is the force exerted on the earth by the satellite, is that a "centrifugal force". I don't think so. I think you have to reexamine your first year college physics textbooks. --AN

It would be useful if you dated your comments, it's much easier to follow the dates that way, rather than checking the history. I agree with Rjstott for the purpose of Wikipedia. AN, whoever you are, you are surely a person whith a scientific background. You certainly don't need this article in Wikipedia to explain the centripetal force. I wrote the following paragraph in the article:

It is important to understand right from the start that there is no 'default', 'natural' centripetal force. By default, objects tend to move in a straight line, as Newtonian mechanics teaches, away from the 'orbit', so in this context, by default there is only a centrifugal force at work. The centripetal force is being applied either by accident (meteors orbiting a planet) or artificially (satellites orbiting Earth, the object at the end of a rope etc). Therefore, the centrifugal force is a natural component of a circular movement, while the centripetal force is what we conventionally call the force keeping the object 'in orbit'.

That paragraph has since been removed in favor of a more scientific approach. While I can agree that the statements in my explanation might have been misleading or imprecise from a scientific perspective (which is why I didn't revert the subsequent changes), I think they are a lot easier to understand by the person who needs to be explained how the centripetal/centrifugal forces work intuitively. Again, I will not fight for that paragraph, but I would like to see something easier to understand for the casual reader in the introduction.

Let me explain what I mean with my "intuitiveness" concern by using the following example: When a kid spins a rock at the end of rope he intuitively feels the centrifugal force. You will say that's not correct, he is applying the centripetal force, that's what he feels. But by that standard it would be difficult to explain gravity -- following the same rationale, when you lift a suitcase you apply "antigravity" to it. However, the kid will intuitively feel that he's "beating" some force; when you explain that the downward force is called gravity and it's real, he's ready to accept that, although he's applying an upward force himself. People intuitively feel the force they need to "beat" as the real force; the force they apply feels like the artificial part of the equation: the upward force to beat gravity is artificial, the gravity keeping the suitcase on the ground is natural. If you explain things the other way around, you confuse the casual reader. The same applies at an intuitive level with centripetal/centrifugal forces IMHO: if you start the article with an introductory statement which says that the centrifugal force doesn't really exist, that confuses the reader ("then what's the force that I'm beating by holding on to the rope? Maybe I didn't get it right...") and s/he's most probably going to miss the point of the whole thing long before you get to formulas. --Gutza 21:57, 14 May 2004 (UTC)

Cleon Teunissen 20:26, 14 Jan 2005 (UTC) I agree with this. To the casual reader, the newtonian description feels wrong. But if you accomodate the casual reader's pre-newtonian conceptions, you may be accused of misunderstanding the physics. It seems to me that the aim of the article should be to educate the casual reader. Misconceptions need to be adressed.

Mi previous comment is undated because, as you can see in the history, it predates the new software with its fancy automatic dating :) The centrifugal force appears when you consider a rotating frame of reference, so, if you want to add a centrifugal force, you can do it talking about that frame of reference. In a non-inertial frame of reference, as the one that follows a stone tied to a rope, there is a centrifugal force, which must me contrarested by the the tension in the rope, the centripetal force..something like that, that still includes the idea of centrifugal force, but is (i think, but I'm not 100% sure) physically more correct. --AstroNomer 21:59, May 16, 2004 (UTC)

"In the case of an orbiting satellite the centripetal force is gravity" - I'm really not sure about calling gravity a force - isn't it a field? The satellite's weight provides the centripetal force, I did change this once but my change has been reversed. Opinions? Drw25 15:44, 17 Oct 2004 (UTC)

Yes, and weight is mass*gravity. Gravity is a force that acts on anything with a mass. The satellite included. 134.153.18.39 17:28, 28 Oct 2004 (UTC)

If it's present in one frame it's present in all frames

In the article it is stated:

In a corotating reference frame, a particle in circular motion has zero velocity. In this case, the centripetal force appears to be exactly cancelled by a pseudo-force, the centrifugal force. Centripetal forces are true forces, appearing in inertial reference frames; centrifugal forces appear only in rotating frames.

That doesn't make sense.
Whenever the velocity of an object is changed by exerting a force, inertia manifests itself. When you hit the brakes of a car, the grip of the tires on the road is necessary for decellerating the car. If an electric car designed to regain energy on decelleration is switched to braking, the manifestation of inertia drives the generators, recharging the car's battery system. Manifestation of inertia can be very powerful, but manifestation of inertia cannot prevent change of velocity, because the power of inertia only manifests itself when there is actual change of velocity.

The same story in the case of centripetal acceleration. There is manifestation of inertia in the centrifugal direction, but this manifestation of inertia cannot prevent the centripetal force from maintaining the circular motion, because the power of inertia only manifests itself when there is actual change of velocity.

The centrifugal manifestation of inertia is present in both the inertial frame and the rotating frame. Going from one frame to another people may ignore it in one frame and acknowledge it in another. Of course, in all frames the same physics is going on, reference frames are mental constructs, changing your perspective from one frame to another is just that: a change of perspective.

Kinematic inertia is like a current circuit with a self-inducting coil in it. This circuit does not offer resistence to current strength in itself, but it does resist change of current strength. The self-induction can/will only jump into action if there is actual change of current strength. --Cleon Teunissen | Talk 23:40, 13 Mar 2005 (UTC)