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Acceleration At Constant Speed? Centrifugal Force?

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#1 Mattzy

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Posted 21 June 2019 - 08:28 PM




We often hear the term "centrifugal force" used commonly in everyday life. I think this is not correct. Are we not really meaning centripetal reaction? It is also said that objects moving at constant speed in a circle are accelerating towards the centre of the circle. This does not seem right to me.
The spinning or turning driver (say a motor) is the force and the outward effect is the reaction - me thinks.  It is said that when an object is moving in a circle at a constant speed, its velocity is constantly changing (being a vector) and that it is accelerating. This is called centripetal acceleration and for this to happen there must be a resultant force, this force is called the centripetal force. This has always puzzled me and seems incorrect. I was never convinced even at school. I postulate: Constant speed is constant speed - there is no acceleration. The object wants to continue in a straight line (Newtons 1st) but some other force makes it describe a circle. The reaction felt on (say) a rope or the wall of a centrifuge is centripetal reaction.
If we draw vectors on paper we can see increasing change in a given direction - and therefore acceleration? I have never understood this rationale. It looks like a paradigm against logic. There is no increase in speed. There is no movement towards the centre. I continue to reason that there is no acceleration. A perfect orbit is a perfect equilibrium - and nothing else (I stand to be corrected).
 


#2 VictorMedvil

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Posted 21 June 2019 - 11:04 PM

 




We often hear the term "centrifugal force" used commonly in everyday life. I think this is not correct. Are we not really meaning centripetal reaction? It is also said that objects moving at constant speed in a circle are accelerating towards the centre of the circle. This does not seem right to me.
The spinning or turning driver (say a motor) is the force and the outward effect is the reaction - me thinks.  It is said that when an object is moving in a circle at a constant speed, its velocity is constantly changing (being a vector) and that it is accelerating. This is called centripetal acceleration and for this to happen there must be a resultant force, this force is called the centripetal force. This has always puzzled me and seems incorrect. I was never convinced even at school. I postulate: Constant speed is constant speed - there is no acceleration. The object wants to continue in a straight line (Newtons 1st) but some other force makes it describe a circle. The reaction felt on (say) a rope or the wall of a centrifuge is centripetal reaction.
If we draw vectors on paper we can see increasing change in a given direction - and therefore acceleration? I have never understood this rationale. It looks like a paradigm against logic. There is no increase in speed. There is no movement towards the centre. I continue to reason that there is no acceleration. A perfect orbit is a perfect equilibrium - and nothing else (I stand to be corrected).

 

 

There is an acceleration toward the middle of the object due to something has to counter the mass's motion in a linear direction at every point the object's mass wants to move in a linear path a force is required to pull the object into a circular orbit as there has to be some attraction toward the middle the concept of this is proven to exist in physics via orbits of planets and other circular orbital motion. In planetary orbits gravity acts as the acceleration force toward the middle if the acceleration of gravity toward the middle ceased then the planets would fly off into space in a linear motion instead of going in a circle via gravitational acceleration toward the middle. Why is this you may ask, this is because there must be a force to keep the object in the circle as it naturally wants to travel at a velocity in a linear path, it is just the way the universe works with orbital motion meaning that the circular path itself causes an acceleration outward against the middle while something has to pull it in to keep its path.

 

Loop-FBD1.png

 

figure2.png


Edited by VictorMedvil, 21 June 2019 - 11:18 PM.


#3 Mattzy

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Posted 22 June 2019 - 02:26 AM

Thanks Victor. The diagram will be useful if anyone else want to discuss the matter - but the text and diagram is what I question. I repeat:-

 

I have never understood this rationale. There is no increase in speed. There is no movement towards the centre - and therefore no acceleration towards it. A perfect orbit is a perfect equilibrium - and nothing else (I stand to be corrected).

 

On planetary orbits: As I said, a perfect orbit is a perfect equilibrium - that is between gravitational attraction and Newtons first law.

 

Also: If the diagram is suggesting that the force of rotation is coming from the hand/muscles at the centre, then it can't be placed in the centre! It must be leading and dragging the mass around the centre.  For a rope (which can only pull) there has to be a moment between the centre and the inner attachment point of the rope - this point will describe a concentric circle. A stiff rod could be placed at the centre, it will bend back against inertia and hold a circular motion against what I think should be called centripetal reaction to the driving force of torque.



#4 exchemist

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Posted 22 June 2019 - 03:12 AM

 




We often hear the term "centrifugal force" used commonly in everyday life. I think this is not correct. Are we not really meaning centripetal reaction? It is also said that objects moving at constant speed in a circle are accelerating towards the centre of the circle. This does not seem right to me.
The spinning or turning driver (say a motor) is the force and the outward effect is the reaction - me thinks.  It is said that when an object is moving in a circle at a constant speed, its velocity is constantly changing (being a vector) and that it is accelerating. This is called centripetal acceleration and for this to happen there must be a resultant force, this force is called the centripetal force. This has always puzzled me and seems incorrect. I was never convinced even at school. I postulate: Constant speed is constant speed - there is no acceleration. The object wants to continue in a straight line (Newtons 1st) but some other force makes it describe a circle. The reaction felt on (say) a rope or the wall of a centrifuge is centripetal reaction.
If we draw vectors on paper we can see increasing change in a given direction - and therefore acceleration? I have never understood this rationale. It looks like a paradigm against logic. There is no increase in speed. There is no movement towards the centre. I continue to reason that there is no acceleration. A perfect orbit is a perfect equilibrium - and nothing else (I stand to be corrected).

 

If a velocity vector changes with time, that must involve acceleration. That is what acceleration is.

 

Also, you concede it takes a force to keep an object moving in a circle. What does F=ma tell you?


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#5 Dubbelosix

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Posted 22 June 2019 - 05:24 AM

Centripedal and Centrifugal forces are not forces, I forget though now the slight differences, if there is any difference at all. Will look it up later to see what differences may exist again.



#6 Dubbelosix

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Posted 22 June 2019 - 06:51 AM

I knew there was a subtle difference, you see, its the direction of motion. A collapsing universe for instance, could be considered a centripedal force. Here's a ''soft school'' example.

 

http://www.softschoo...etal_force/458/



#7 Dubbelosix

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Posted 22 June 2019 - 06:53 AM

Centripedal force and even centrifugal psuedoforce are indeed correction terms, they exist blatantly within the geometric algebraic space describing general relativity and has even fundamental applications to an electron.



#8 Mattzy

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Posted 22 June 2019 - 10:54 PM

If a velocity vector changes with time, that must involve acceleration. That is what acceleration is.

 

Also, you concede it takes a force to keep an object moving in a circle. What does F=ma tell you?

Good point exchemist. This is precisely my point. I am saying that the velocity vector is not changing with time. The example looks to me like equilibrium - not acceleration. If there is a change from an existing straight path to a curved path then there will be acceleration until equilibrium is reached, but I don't see continuous acceleration just because the circle is continuous.

I think your argument will be that if we compare the resultant circular path with the projected tangential path then we see an increasing change in velocity vector and therefore acceleration. This is what is taught. But I am saying that the straight line is purely notional in an existing circular path. It is a useful explanation of the outward inertia, but it has no effect, because it is canceled by the inward pull, the notion seems wrong to me as there is no point on the circular path that the mass can accelerate away from. The distance to the centre does not change. All measurements are unchanging.

There is only one path for the mass and that is the resultant circle. There is no acceleration in any direction.

What does F=ma tell me?

In planetary motion Newtons first law keeps the planetary motion and also provides opposition to gravitational attraction. When these are in equilibrium we have orbit - I see no acceleration. So in this case F=ma does not apply. (I am as always, open to correction).

In the case of a centrifuge at constant speed - after it has accelerated to constant rpm (as per the example) - all the forces have reached equilibrium. The turning force from the motor is in equilibrium with the resistant inertia (this is the equal and opposite reaction) and the tendency for the force to continue on at a tangent is balanced by the restraining structure - the reaction will be structural movement / distortion.

On terminology - the force is the driver, the reaction is the result, therefore the outward fling is reaction, not force. We could call it centrifugal reaction.



#9 exchemist

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Posted 23 June 2019 - 05:31 AM

Good point exchemist. This is precisely my point. I am saying that the velocity vector is not changing with time. The example looks to me like equilibrium - not acceleration. If there is a change from an existing straight path to a curved path then there will be acceleration until equilibrium is reached, but I don't see continuous acceleration just because the circle is continuous.

I think your argument will be that if we compare the resultant circular path with the projected tangential path then we see an increasing change in velocity vector and therefore acceleration. This is what is taught. But I am saying that the straight line is purely notional in an existing circular path. It is a useful explanation of the outward inertia, but it has no effect, because it is canceled by the inward pull, the notion seems wrong to me as there is no point on the circular path that the mass can accelerate away from. The distance to the centre does not change. All measurements are unchanging.

There is only one path for the mass and that is the resultant circle. There is no acceleration in any direction.

What does F=ma tell me?

In planetary motion Newtons first law keeps the planetary motion and also provides opposition to gravitational attraction. When these are in equilibrium we have orbit - I see no acceleration. So in this case F=ma does not apply. (I am as always, open to correction).

In the case of a centrifuge at constant speed - after it has accelerated to constant rpm (as per the example) - all the forces have reached equilibrium. The turning force from the motor is in equilibrium with the resistant inertia (this is the equal and opposite reaction) and the tendency for the force to continue on at a tangent is balanced by the restraining structure - the reaction will be structural movement / distortion.

On terminology - the force is the driver, the reaction is the result, therefore the outward fling is reaction, not force. We could call it centrifugal reaction.

I think you have in effect decided that you don't believe in vectors! A vector has both magnitude and direction. If you want to change the direction of a supermarket trolley, you have to apply a sideways force to accelerate it in the new direction while decelerating it in the previous direction (in practice you may be able to let friction do that for you). The trolley follows a curved path during the process as the velocity in the new direction builds up.

 

Circular motion is just a special case of this.

 

If you want, you can always consider circular motion from the viewpoint of the frame of reference of the rotating object. But then you will feel an outward (centrifugal) force, which depends, rather bizarrely, on the rate at which the universe rotates around you.

 

You can work with this alternative mechanics if you like, but it can get a bit difficult.  


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#10 Mattzy

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Posted 24 June 2019 - 12:28 AM

I think you have in effect decided that you don't believe in vectors! A vector has both magnitude and direction. If you want to change the direction of a supermarket trolley, you have to apply a sideways force to accelerate it in the new direction while decelerating it in the previous direction (in practice you may be able to let friction do that for you). The trolley follows a curved path during the process as the velocity in the new direction builds up.

 

Circular motion is just a special case of this.

 

If you want, you can always consider circular motion from the viewpoint of the frame of reference of the rotating object. But then you will feel an outward (centrifugal) force, which depends, rather bizarrely, on the rate at which the universe rotates around you.

 

You can work with this alternative mechanics if you like, but it can get a bit difficult.  

Yes, I suppose circular motion is a special case of vectors. I concede that if we turn to the right from a straight path (in a vehicle) to a curved path we accelerate towards the right. What has always troubled me is the constant circular motion and how it is described. ie. acceleration towards the centre, and centrifugal force (I stll see this as a reaction - but it doesn't really matter what we call it so I'll let that one drop)



#11 Dubbelosix

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Posted 27 June 2019 - 03:23 AM

Not only that, but where there is a curved path taken, even for particles, there is by direct translation a concept of gravity from gravity. This is probably the only way we can quantize gravity - its a not a true quantization, but what it demonstrates is that a refractive index for instance, has quantum solutions, not in the form of particles, but as a part of curved motion. I am so convinced that gravitational waves are an accoustic wave, that we will learn a great deal from a new type of understanding behind how we view gravity itself. 



#12 Dubbelosix

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Posted 27 June 2019 - 03:29 AM

I'm probably not giving myself enough credit, I know enough about magnetohydrodynamics to know that the cross products behind the potential [math]A[/math] is related to the same equations described through maxwell's equations. I know that it applies to fluid like systems right down to the sun for example, but I am still in no position to give advice how to relate it to the other topic, because it wasn't until the other day I looked into it. But teaching oneself about such things, can be so very rewarding. 



#13 Mattzy

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Posted 28 June 2019 - 03:26 AM

Not only that, but where there is a curved path taken, even for particles, there is by direct translation a concept of gravity from gravity. This is probably the only way we can quantize gravity - its a not a true quantization, but what it demonstrates is that a refractive index for instance, has quantum solutions, not in the form of particles, but as a part of curved motion. I am so convinced that gravitational waves are an accoustic wave, that we will learn a great deal from a new type of understanding behind how we view gravity itself. 

If the gravitational wave is acoustic then what is the medium? Electromagnetic? Gravitational force seems strongly dependent on proximity to mass irrespective of electromagnetism.



#14 exchemist

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Posted 28 June 2019 - 07:24 AM

If the gravitational wave is acoustic then what is the medium? Electromagnetic? Gravitational force seems strongly dependent on proximity to mass irrespective of electromagnetism.

In conventional general relativity, the medium transmitting gravitational waves is spacetime itself. 



#15 Mattzy

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Posted 29 June 2019 - 08:46 PM

In conventional general relativity, the medium transmitting gravitational waves is spacetime itself. 

How do we separate the debunked ether from a spacetime medium that facilitates waves? 006 is suggesting acoustic transmission which also suggests a substance - normally acoustic means compression waves I think.



#16 Dubbelosix

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Posted 29 June 2019 - 09:21 PM

Spacetime is not nothing, a gravitational wave is not a substance and the medium itself is not mediated by a particle - understand this, the medium responds to all kinds of energy, all types of matter, but it is not mediated by a graviton. What things are mediated in, is a thickness of the gravitational field which varies from planet to planet, from a position in space to another. This is why inertial effects tend towards zero in a vacuum, while here on Earth, inertial effects are quite dominant.

 

The ether wind, is what has been debunked - there was no backlash of the Earth moving through a medium made of particles, because that medium is not made from observable particles. No backlash of gravitons either, because gravity is a pseudo-force, more akin to the magnetic field which relies on the moving frame of reference. A gravitational wave, is an acoustic wave, in the sense that a ripple in the medium will cause a compression on real substances, but it also separates, it is not an effect which cannot be undone, hence why acoustic waves are both transverse and longitudinal.

 

It is only in spin-2 graviton tensor theories, that they have been assumed to be transverse only. But a true acoustic wave does not behave like this.



#17 Mattzy

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Posted 01 July 2019 - 01:58 AM

Spacetime is not nothing, a gravitational wave is not a substance and the medium itself is not mediated by a particle - understand this, the medium responds to all kinds of energy, all types of matter, but it is not mediated by a graviton. What things are mediated in, is a thickness of the gravitational field which varies from planet to planet, from a position in space to another. This is why inertial effects tend towards zero in a vacuum, while here on Earth, inertial effects are quite dominant.

 

The ether wind, is what has been debunked - there was no backlash of the Earth moving through a medium made of particles, because that medium is not made from observable particles. No backlash of gravitons either, because gravity is a pseudo-force, more akin to the magnetic field which relies on the moving frame of reference. A gravitational wave, is an acoustic wave, in the sense that a ripple in the medium will cause a compression on real substances, but it also separates, it is not an effect which cannot be undone, hence why acoustic waves are both transverse and longitudinal.

 

It is only in spin-2 graviton tensor theories, that they have been assumed to be transverse only. But a true acoustic wave does not behave like this.

This is completely new to me. What inertial effects tend towards zero in a vacuum? Inertia can be multiplied by mass and force ie. gravity, and velocity but what relationship is there between inertia and gravity?

I wonder if there is any analysis of the fundamental question: Why (or how) does mass carry inertia? Did newton leave with his laws without further analysis? Mass on collision with another mass can pass on it's inertia to completely give up its velocity and pass it on like those swinging steel balls. It is interesting that the movement is passed on. I think we could just as easily accept that the movement is completely stopped by an equal mass (if it were so).

I wonder if inertia is something more tangible like gravity or spacetime that is not fully explored.





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