Any mass in motion has inertia. A mass that is accelerating is being acted upon by a force. A mass travelling in an orbit, constrained by a string is under constant angular acceleration as a result of the centripetal force imposed by the string. You are correct in saying centrifugal (literally "center-fleeing) force does not exist and that when the string is released the mass will have only momentum (and of course kinetic energy), but that's true of any mass when the force that gave it acceleration is released.
While the mass is orbiting on the string, the center certainly does experience a force along the line of the string toward the orbiting mass and this force is equal in magnitude but opposite in direction to the force acting upon the mass. For whatever reason, one got the tag centifugal force - even though there is really only one force acting on the mass to hold it in orbit, the centripetal force. But it too ceases to exist when the string is released.

But force and inertia are not the same, any more than gravity and weight are the same. They are intimately related through some very simple laws, but they aren't the same. It's tempting to say force is that which causes acceleration of a mass - and in a frictionless world (where only inertia resisted changes in momentum) this would be a good definition. The billiard ball isn't moving under its own force, but to be sure some force was exerted on it to give it momentum, and that momentum has the potential to exert a force on any other billiard ball that gets in the way.

This is my convoluted way of saying I don't think force and momentum are the same thing, either mathematically or in the imprecise written word.

First off i you think i`m posting the same thing again and again feel free to ignore me,i think i may be babbling to get things clear in my own head.
The centrifugal force seems to only not exist in the newtonian analysis of the situation. There you can use a reference frame that is non rotating and includes the on body rotating around the other. The newtonian view allows you to invoke absolute space and say that this frame of reference is the correct one and a frame based on the surface of the earth that is rotating is less 'correct' than the other. This in turn allows you to say that the centripetal force is real (its in the absoulute space static frame) and that the centrifugal force is just an ficticious force(because it presents itself only in your 'less' correct rotating frame).
If you take a more relativistic approach neither frame is more correct than the other and there is no absoulte space so each frame can claim that the force it sees is the real one (rotating frame sees centrifugal..its real! static frame sees centripetal..thats real centrifugal is ficticious!).

The proof that so-called *centrifugal force* is not a force, but is *inertia*, lies in the fact that when the object being held (restrained by a barrier) in a circular path is released, it travels off at a TANGENT to the curve and not RADIALLY, as it would travel if it indeed were a force and not inertial.

That is true if you select the non rotating frame, but consider the path of the object in a rotating frame. It can be seen to move in a line directly away from the observer,that is the behavour one would expect from a force isn`t it? Initially i also used the tangent argument but it the time i had only considered the static frame.

The old twentieth century model is starting to show signs of wear and tear and is becoming so passé
Its strange then that it seems to be the older newtonian model which presents centifugal force as ficticious and 20th century relativity that allows it to be real from a certain point of view.

jumbothat sounds like a pretty good analysis to me. However you have to keep in mind that even in the rotating frame the centrifugal force has no source, so you can't entirely get rid of the pseudo force label.

I wanted to add a little to what Jumbo has already said. For Newtonion mechanics and SR the rotating frame is not a valid reference frame: a valid reference frame is a non-accelerating frame. The Galilean and Lorentz transform will fail if you try to convert to a rotating frame. It's not necessary to invoke pure absolute frame, only an inertial (non-accelerating) one.

In general relativity the definition of force is much looser than in Newton's. In GR gravity is just curvature of space, but what causes an object to move along the curve? Consider an object at rest with respect to a black hole, eventually that object will fall into the black hole. Since gravity is now "curvature", no "force" caused the motion. For GR, our definition must be loosened. A force in GR is anything that causes a change in momentum, F = dp/dt.

<font size=-1>[ This Message was edited by: Wiley on 2002-07-09 12:30 ]</font>

Puzzle time! See if you can find my response to your reply.

In the Principia, LAW I, Newton did indeed state his idea as “uniform motion in a right line” (straight line). However, in his immediately preceding paragraph he wrote “…two globes, kept at a given distance one from the other by means of a cord that connects them, … revolved about their common centre of gravity….” Newton’s first law in no way precludes that those globes, in a friction free environment (e.g. outer space), would also continue their state of uniform revolving motion “unless compelled to change that state by forces impressed upon” them. Binary star systems (e.g. the Algol twins) have certainly been doing that for a long, long time. Newton’s laws are excellent, as far as they go. However, even in Newtonian physics they should go farther. They should, for example, include the inertia of revolving systems. A JOURNEY BEYOND THE UNIVERSE presents some more needed Newtonian additions to Newton’s laws.

Let us quantify the anguish of excommunication and name the unit after Galileo. Let 1 Galileo represent what he felt because of his excommunication. Thank you for the 1 picoGalileo. It helps me to appreciate his situation a little better.

Aristotle wasn’t even up to date on 17th century physics, but his laws of logic are timeless. Keep context and simultaneity in mind. The contexts are not the same (nor is the experimental apparatus) when a photon is viewed as wave or particle. Once a photon is detected it is no longer the same thing. No one has simultaneously detected both the wave and particle aspect of the same photon. Maybe it is never simultaneously a wave and a particle. Perhaps it oscillates between those two aspects. We do know that it’s an infinitely high Q, natural born oscillator. [img]/phpBB/images/smiles/icon_wink.gif[/img] The equivalence of mass and energy does not mean that mass is identical to energy. Although mass can be converted to energy, it is never both at the same time. Furthermore, the conversion is a sequential process that requires specific conditions for each known isotope reaction. Whether it is to be viewed as mass or energy depends, again, on context.

It is important to agree on the meanings of terms used in discourse. Otherwise we can have misunderstandings. When I use the term ‘centripetal force,’ I mean a force directed toward a center of revolution. By ‘centrifugal force’ I mean a force directed away from a center of revolution. For every force there must be an equal and opposite force. Thus, if a centripetal force exists, an equal and opposing centrifugal force must exist. The motion of revolution, being at a right angle to those forces, cannot be the result of either of those forces.

Here it is folks! The perfect gift for young and old alike. The DO-IT-YOURSELF TWENTYFIRST CENTURY PHYSICIST SET from HECO. Amaze your friends! Discover truths about the world we live in! Have Fun! It’s so easy to use that even a child can follow these simple directions.

First open the box. In it you should find:
(1) virtually weightless, long, transparent, plastic pipe with outside (male) thread on one end and two transverse holes on opposite end.
(1) virtually-weightless transparent pipe cap
(1) virtually-weightless helical compression spring coated all over with compression-sensitive red phosphorescent paint (labeled C)
(1) virtually-weightless helical tension spring coated all over with tension-sensitive green phosphorescent paint (labeled T)
(1) virtually-weightless extra-strong spring connector
(1) swivel-handle with hook end
(1) extra-heavy solid platinum ball

Please check to make sure the springs are not damaged or defective. Squeeze the compression spring between your hands and it should glow with red light and you should feel it pressing against your hands. Pull it from both ends and you should see no red glow. Lay it on a really smooth table and you should see no red glow. Pull the tension spring from both ends and it should glow with a green light and you should feel the resistance it offers to your pulling. It should not glow when compressed or when lying on the table. These springs serve as force detectors. They are guaranteed to be equally effective and foolproof in any frame of reference e.g., stationary, uniform linear motion, accelerated linear motion, rotating, etc., in any multi-dimensional continuum, in any space no matter how curved, and even at relativistic speeds. Furthermore, they have a money-back guarantee to be completely unresponsive to imaginary, false, fictitious, merely assumed, or purely hypothetical forces as well as to any kind of non-force.

Experiment 1. With spring C lying on the table, push one end of it. You will feel no opposition at all. It will slide all over the table, but will not glow. Notice that you cannot even generate a force with nothing opposing your hand. That is indirect support for Newton’s third law. Although the third law is in terms of action and reaction, Newton’s first law required forces to generate motive action and reaction. Thus, the third law presumes the first law and applies the notion of ‘equal and opposite’ to forces as well as to action and reaction. That Newton was aware of the foregoing is evident because in the second sentence of the explanatory paragraph immediately following Law III he wrote “If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back toward the stone;…” Newton, therefore, explicitly included force in his notion of action and reaction.

Experiment 2. Screw the pipe cap onto the threaded end of the pipe. Insert the compression spring into the pipe. Next, insert the platinum ball into the pipe. Now hold the pipe vertically with the cap, spring, and ball at the bottom. Spring C should now be visibly compressed and glow a bright red. This demonstrates that gravity can produce a force.

Experiment 3. Leave the spring and ball in the pipe. Lay the pipe on a smooth floor. With one hand push against the pipe cap for a second or two. While you are pushing the spring will display its red glow. When you stop pushing the glow will instantly cease. Because the spring will only glow when pushed from both its ends, this experiment demonstrates that the ball tries to resist being moved by generating a force opposing the force of your hand. The resisting force of the ball was created by the inertia of the ball. The inertia of the ball performs another task whether a force is pushing it or not. It constantly and simultaneously watches in all directions for any new force to resist. It is always ready, at moment’s notice, to almost instantly throw its resisting force in any required direction. Its aim is always perfect. It never misses. In a very similar way, it almost instantly withdraws its force whenever any force acting against it gives up and withdraws. (‘Almost’ because there can be no infinite propagation velocities, especially where action at a distance is involved.)

Experiment 4. Leave the compression spring and ball in the pipe. Pass the L shaped end of the spring connector through the holes in the open end of the pipe. Fasten one end of the tension spring to the free end of the spring connector. Fasten the swivel-handle hook end to the other end of the tension spring. Holding the swivel-handle, swing the whole assembly over your head with a circular motion. You will observe that both springs are glowing brightly, each with its own color. The red glowing spring has been compressed by and has detected the centrifugal force of the platinum ball. That force is clearly directed radially outward in line with and away from the center of rotation. The green glowing spring has detected the forces in opposition at your end of the pipe, i.e., your centripetal force and the ball’s centrifugal force. These observations demonstrate that centrifugal force is as real as can be.

Diagram of experiment 4:
….……C….………………..….…….….…T
…...|////////////O ball..…………………..|\\\\\\|_________+ center of
cap |____________________________| pipe……………….….rotation

…… merely typographic placeholders

Note that in one respect experiment 4 is quite different from rope and rock experiments, and seems quite different from the situations in celestial mechanics. In experiment 4 the centripetal force acting on the ball does not pull from inside the orbit of the ball toward the center of rotation, as in those other experiments. It pushes from outside the orbit of the ball toward the center of rotation.

A person being subjected to centrifugal force, as in some NASA tests, sits facing the center of rotation in a chair fastened to the end of a rigid rotating arm. The person sitting in the chair is pressed against the revolving chair as much as it presses against her/him. The test subject feels not only the centripetal force of the chair against her/his back, but also the centrifugal force of her/his abdominal muscles and innards against her/his back. Healthy proprioceptive sensors do not lie. NASA, and especially its employees who have been centrifuged, cannot but consider centrifugal force to be a real force. Experiment 4 is similar to those NASA tests in that the centripetal force pushes toward the center from outside the orbit of the test object.

Some people may tell you that the platinum ball is continuously falling toward the center of rotation and is accelerating in that direction. Ask them how the ball, so continuously busy falling and accelerating toward the center, ever finds time to push in the exactly opposite direction and compress the spring. Some people will also say that the ball is accelerating in free-fall. Ask them how a ball in free-fall can compress the spring against a rigid structure. Some may even go so far as to say that there is no such thing as centrifugal force. Ask them to name the forces that compressed the spring or to explain how a nonexistent force can compress a spring.
_____________________________________
*…my gifts displayed for you in loyal love
you must not scorn before you grasp their meaning.* Lucretius

BZZZZT!! again

We do not live in a simple Newtonian universe.

The two revolving globes will lose energy and slow down due to loss of gravitational energy.

Newton's laws are a good first approximation. Einstein's relativities are a better formulation and may be superceded in the future. IF that happens, relativity will still be a good approximation in most circumstances (just as Newton's "laws" are now.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Kaptain K

Gravitational energy loss has no bearing on Newton’s two globes because the globes do not constitute a gravitationally bound system. Their gravitational potential energy is so completely negligible compared to their kinetic energy of rotation that a cord is required to bind them. Were they to lose their gravitational energy by some as yet unknown process, their angular velocity (RPM) would not be altered.

Gravitational energy of a system can only be lost in the form of electromagnetic radiation (emr) from the system or as actual loss of mass. The former loss takes place when gravitational potential energy is converted to kinetic energy and subsequent friction, fusion reactions, fission reactions, or collision reactions generate emr that leaves the system. The latter loss requires reactions that create mass particles with energy high enough to at least assure escape velocity. The processes for gravitational loss of energy are irrelevant to Newton’s globes.

More re centrifugal force:

Thinking about the rope and rock, I realized that the centripetal force is also applied by the rope to the rock from outside rather than inside of the rock’s orbit. Centripetal force could be applied from inside the orbit of the rock if we fastened the end of the rope to the rock with a high-strength adhesive, for example. In the Principia Newton described two cases where the centripetal force is applied to the far side of the orbiting object. The first is in his description of a stone whirled around in a sling, stretching the sling. The second is in his spinning bucket of water, where the wall of the bucket applies centripetal force (opposing the centrifugal force of the meniscus forming, orbiting water) from outside the orbit of the water.

Now I will let you in on a secret my readers already know. In A JOURNEY BEYOND THE UNIVERSE I show that so-called gravitational attraction is a result of repelling forces on the far side of objects that push them together. That is why I knew that centrifugal force had to be a real force. Perhaps, in a century or two, gravity will be recognized as a repelling rather than attracting force and will be properly called gravitational repulsion. From that new viewpoint, celestial mechanics, Newton’s stone and sling, the NASA centrifuge tests, and the ball and spring experiment have forces similarly oriented.
-------------------__________________________________________________ ________
*It is not easy paddling upstream alone.
It is even harder against the mainstream.* Hanak
__________________________________________________ ________

Nope. The rotating weights are a gravitational dipole (regardless of how they are bound) and will radiate gravitationally (not electromagnetically).

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-07-14 14:53 ]</font>

Forgive me for being pedantic, but gravitational radiation cannot be generated by a dipole moment, only a quadrupole moment will do the job. This is because no matter how a system of masses move they cannot have a dipole moment.

If you have two unlike charges on each end of a spinning rod then you have an electric dipole moment, but if you have two like charges then you can only have a quadrupole (or higher) moment. Since all mass has, in effect, has the same charge the same reasoning applies.

But you are certainly correct in saying that two masses will only radiate gravitationally.





<font size=-1>[ This Message was edited by: Ring on 2002-07-14 23:31 ]</font>

Ring,
I thank you for the correction. I also appreciate you backing me up. I knew that they would radiate, but I was a little fuzzy on the mechanics. You don't want to know how long ago college was*.

*Hint: Saturn was the only planet with rings!

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Kaptain K and Ring:

On 2002-07-14 14:51 Kaptain K wrote:
Where would the implied lost angular momentum reappear in order to be conserved?

DUH! As gravity waves, what else?

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Kaptain K’s statement attempted to claim that Newton’s first law was not valid for two globes connected by a cord and rotating about their common center of gravity. To the best of my knowledge gravitational radiation has not been detected directly. The evidence for that radiation is indirect: e.g. an eight-hour period of a binary pulsar system observed to be decreasing by 75 microseconds per year. If that system existed and began its rotation 15 billion years ago, it would have lost only about one one-thousandth of its angular velocity by now.

So when he says that Newton's globes would lose angular velocity via gravitational radiation, his claim that therefore Newton's first law doesn't apply to his globes seems like hair-splitting of some hairs that are already very, very fine. For all we know a similar argument might be made against Newton’s first law really applying to linear motion of a body. A more fundamental refutation of Kaptain K’s claim follows.

The laws of angular motion are analogs of Newton’s three laws of linear motion. Here is the first law for rotating motion. A body in rotation will continue to turn about a fixed axis with unaltered angular velocity unless acted upon by an external torque-producing force.

Note that the first law for rotating motion does not restrict the shape of the body in rotation. That body could have a rigid dumbbell shape, or could have a wire-like section connecting the two globular ends. Thus, there is no reason that Newton’ globes and cord would not be subject to the same law.

In A JOURNEY BEYOND THE UNIVERSE the existence of gravity waves and gravitational radiation arises without recourse to relativity theory. Let us examine their relationship to Newton’s globes. In order to support wave motion a medium must present a finite, non-zero impedance to the generation and propagation of the wave. That impedance represents a real, physical force to be worked against in those processes. Both zero impedance and infinite impedance preclude any energy transfer. The impedance of free space is a well-understood and quantified property (377 ohms) for electromagnetic radiation. The force associated with the impedance of space for gravitational radiation would have to act against the globes’ motion in order for energy transfer to result in the generation of gravity waves. That force is certainly external to Newton’s globes; and therefore, Newton’s first law (in the form of its analog for angular motion) remains valid for Newton’s globes and cord..

On 2002-07-18, in reply to my asking where the angular momentum lost by Newton’s globes would reappear for conservation, Kaptain K wrote:
The question is deeper than a superficial reading of it might suggest. Certainly anything carried away from the globes must be carried by gravitational radiation. Since the energy transported by the wave will be related to the amplitude of the wave, we can look to the amplitude for the energy. The angular velocity of the globes will appear as the frequency of the wave. How will the wave carry the angular momentum?

Think of the question in reverse. Assume a gravity wave detector aimed at a right angle to an approaching gravity wave front. When the wave passes through the detector we would expect the detector to oscillate in the propagation direction of the wave. The magnitude of the oscillation would be proportional to the amplitude of the wave. The frequency of the oscillation (with a compliant detector) would be that of the wave. The wave has given up some of its energy in moving the detector. How would the wave transfer the corresponding quantity of angular momentum to the detector? In other words, how would the wave produce torque on the detector?

Although both quantum mechanics and wave mechanics preclude the continuous loss of energy to which you refer, they do not preclude the balancing of electrostatic attraction by centrifugal force in the allowed orbits. If the quantum number is greater than 10,000 for the electron orbiting the hydrogen atom, the frequencies of the emitted light calculated by quantum mechanics and classical mechanics differ by only 0.015%.
Perhaps there has not been a response because the questions were put too obliquely. Let me reframe the issue in a direct form and address it to the ‘centrifugal-force-is-not-real-camp’ whose members include DaveC, jumbo, Kaptain K, ljbrs, Ring, and Wiley. Do you still claim that centrifugal force is not a real force? If you answer yes, then what forces compressed the spring? If you are undecided, let us know the nature of your dilemma. Maybe we can help you resolve it.

you know the force you feel on the string isn't technically centrifugal force, what you are feeling in the tension on the string. if you had a bucket filled with water, then the water would be experancing centrifugal force. The tension on the string is in responce to Newton's third law of motion. For every action their is an equal but opposite reaction.

Also forces are applications of energy, the only energy that is being imparted in the bucket on a string experiment is the energy from your arm, every thing else is a reaction to that imparted enery, therefore there is only one 'real' force.

_________________
The universe is not only queerer than we imagine, it is queerer than we can imagine.
J. B. S. Haldane

<font size=-1>[ This Message was edited by: moving_target on 2002-07-26 23:48 ]</font>

Hold on, I thought someone said that technically there is no such thing as centrifugal force. [img]/phpBB/images/smiles/icon_smile.gif[/img]

Details, details [img]/phpBB/images/smiles/icon_razz.gif[/img]

Aw, see, I tried to stay out of this discussion because of all my previous posts on "centrifugal force," but now I've been left off Hanak's list! [img]/phpBB/images/smiles/icon_frown.gif[/img]

In your fourth experiment, instead of spinning the contraption around your head, just lay it on your smooth floor and pull it length-wise. The spring will be compressed by the ball's inertia, just like it did in experiment 3. It is this same "force," inertia, which compresses it in experiment 4.

I just fail to see why spinning it instead of sliding it turns the ball's "inertia" into "centrifugal force." [img]/phpBB/images/smiles/icon_smile.gif[/img]

__________________
SeanF

"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

The contents of this post are ©2008 by SeanF and may not be copied or retransmitted in any form without the express written consent of SeanF

First, wave mechanics does not preclude the energy loss I'm refering to, only quantum mechanics does. If wave mechanics did preclude this loss, there would have been no reason to develop quantum mechanics.

Second, by having the electron moving in an orbit, you are no longer in an electrostatic regime, but an electrodynamic one. You must deal with the synchrotron radiation.

Third, classical models of the atom do have a limited range of validity. It's not surprising that there is a limited range your in which your model works, but we need a model that is valid over a large span.

Fourth, a quantum number of 10,000? for t