John2020

2 minutes ago, Ghideon said:

The measured acceleration may vary and is always towards the center*. The acceleration may look different from different frames of reference such as a rotating or an inertial frame of reference. 

Your argumentation is all about an inertial frame. I speak about the rotating frame. So there it cannot be towards the center since there we have the centrifugal that is greater than the centripetal during the increase in angular velocity.

7 minutes ago, Ghideon said:

May I advice you to focus one the other more serious issues pointed out?

You mean about the Euler force?

1 hour ago, Ghideon said:

*) Again, as noted earlier In a perfectly tuned setting the accelerometer attached to mass m could possibly measure exactly zero during a short time. 

That cannot be true along the rigid rod (we speak always about the mass m accelerating radially). 

12 minutes ago, Ghideon said:

Does the concept of "Euler force" ring a bell? Given the title of your speculative thread the tangent force Swansont mentions should not be too unfamiliar.

But the Euler force is being developed along the axis of rotation. We don't have any mass there that would be influenced. That could be utilized if the mass m and the rod would on the z-axis (as seen from screen). It means the rod and the mass along the axis of rotation of mass M. It is a good alternative for my next challenge.

3 minutes ago, Ghideon said:

No. 

Don't forget I speak for the transition time where the centrifugal > centripetal and not while they are equal (thus zero acceleration).

8 minutes ago, Ghideon said:

Here is one source of confusion. When you say that mass m will accelerate outwards, you mean as seen in the rotating frame, OK? 

What will an accelerometer, attached to the mass m, show? Number not important yet, just direction. 

Before I wrote those points, I mentioned "Rotating Frame (Fictitious Forces)". So, for the rotating frame it will be outwards as also the accelerometer (we speak always for mass m) will show the same direction.

12 hours ago, swansont said:

You haven’t accounted for the change in angular speed. So you now have rotation in your rotating frame (have fun analyzing that). There must be a tangential force acting in order for this to happen.

I don't understand what you actually mean. Both are provided by the motor (inner mechanism, power etc) and transferred through the rigid rod.

2 hours ago, Ghideon said:

I have never experienced that. I have experienced a centripetal force resulting in a net force F>0 resulting in a change of direction AKA acceleration. (Given seatbelt is fastened and / or car door shut)

I have also, as an engineer, experienced the efficiency of introducing a fictitious force such as centrifugal force to allow for calculations in an accelerated frame of reference.

Being inside a car driving in a curve you are in a rotational frame that implies what you experience is a centrifugal force that creates a pretty physical outwards acceleration when you are on board.

2 hours ago, Ghideon said:

Note that in the inertial frame of reference the mass m never accelerates out from the centre in your example. An accelerometer onboard the mass m will never register an acceleration* away from the circle centre, only a varying acceleration towards the centre. 

*) In a perfectly tuned setting the acceleration could possibly be exactly zero (onboard the mall and in the inertial frame of reference) during a short time. 

There is a problem here. In both cases the coordinates of the mass m will appear away from the center because we have a change in angular velocity. How you say the acceleration is towards the center in both cases? Such claim brings the inertial and rotational in disagreement. I suppose this is a mistake in your description.

I would understand the above for the inertial frame, however when we are in the rotating frame the role of varying centripetal (the difference actually between two subsequent angular velocity values) is taken by the varying centrifugal force.

There are some points that for me up to now have no satisfactory explanation as given from your side (as forum).

Rotating frame in my example (fictitious forces)

a) The role of centripetal is taken by the friction force

b) When the angular velocity is constant, the centripetal and the inertial centrifugal force are equal that keeps the mass at point r1 or moves with constant velocity (assuming to be very small due to limited rod length)

c) During the transition to a greater angular velocity value, the centrifugal becomes greater than the centripetal

d) Due to (c) the mass m will acquire a radial outwards acceleration (since we have a change in angular velocity)

e) Due to (d) for a mass ratio e.g. M/m=10/1, the CoM changes and accelerates in the same direction as the mass m

Conclusion: Since the acceleration of mass m is caused by the inertial centrifugal force (considered fictitious), there will be no counteracting force upon the rest of the system that implies a change and acceleration of CoM of a system is feasible.

Note: swansont assumed m<<M in his analysis so there will be no change and in CoM that is OK. 

7 minutes ago, Ghideon said:

Non-real forces (fictitious) have no physical effect. You seem to have missed that point. ( but you agreed on it in the earlier analysis)

Then how you explain the acceleration of mass m? The fact we experience the centrifugal force while being in a car driving over a curve, it is a physical effect. Otherwise, it is like being in denial that inertial forces exist. What I agreed was we don't have fictitious forces in an inertial frame.

6 minutes ago, Ghideon said:

"the obvious" ? 

The obvious can be identified in the rotating frame easily: On my example as long as the angular velocity changes, the  centrifugal force increases (net force is not null -> centrifugal > centripetal) results in accelerating mass m radially. At that particular time frame this change is not counteracted by a force upon the rest of the system because the centrifugal is by nature inertial (not a real force. If it was a real force then I would agree with you. This is the point you all miss.). Thus, the acceleration of mass m results in an accelerating change of the CoM of the system as a whole.

5 hours ago, swansont said:

A table leg doesn’t move, but exerts a force to keep whatever’s on the table from falling to the ground.

Your assessment of what is and is not possible needs to be based in physics, not fantasy.

5 hours ago, swansont said:

There is always a reaction force in an inertial frame. The rod exerts a frictional force on the mass, the mass exerts a frictional force on the rod.

5 hours ago, swansont said:

You keep asking if there’s a reaction force, like you’re hoping that someone will eventually say, “no”

In our case you overlook an important detail, there is a mass transfer that implies an accelerating change of the CoM. The situation has nothing to do with the normal forces and the table. You are fantasizing things that do not hold. Lastly, I am not hoping someone will eventually say, "no", but to acknowledge the obvious.

Next time, I would suggest you to make the same exercise with the hammer (as Ghideon proposed) or to think the situation of a passenger in a car while is taking a curve by changing the speed slightly.. 

6 minutes ago, Ghideon said:

So the simplest thing you could imagine is that all of Newton, Lagranage, Hamilton, Einstein, and down to the core of knowledge is wrong*. Your definition of "simple" seems to deviate from my definition. 

I didn't say that. The problem is I searched in the entire web to find physics exercises that address this kind of problem (as I proposed with my last drawing), however I found none. Do you have any resource that may show a detail solution to this specific problem (non-rotating and rotating frame of reference)?

10 minutes ago, Ghideon said:

Does your answer imply that you are not prepared to move back to basics and try again? 

When something does not fit well, I have always doubt (and eventually I am right about it). I need a detailed and clear mathematical analysis based on classical mechanics (No Lagrangians, no Hamiltonians and stuff). If you have any resource on this, please share it with us. The way we handled this problem through the thread was 99.9% based on texting and not maths, meaning what we exchanged was just views/interpretations, no proofs and no real life observations.

13 minutes ago, Ghideon said:

Thats cool, we knew that your claims were incorrect according to known laws of physics from your very first post. Question was if you wanted to stay wrong or eventually learn more physics. 

No thanks. I already learnt a lot.

13 minutes ago, Ghideon said:

Me and @swansont will reach the same conclusion regarding inertial vs rotational frame of reference as long as we are able to make identical interpretations of your instructions. It can't be any other way since we use the same physical rules, principles and laws. I guess performing such an analysis will have to wait till such a time when your level of understanding matches the required explanations.

When you make the analysis on the rotating frame, I am convinced 99.9999% that your view on this matter will be wrong because you follow of what is familiar to you, thinking that will never fail and you will ensure that you will not get embarrassed (don't forget you are a member of this forum having a good reputation). 

15 minutes ago, Ghideon said:

Have you seen any support for your Newton circumvention here during the discussions here?
Also not that this is just about some minor details of one specific example. The big picture regarding all possible examples and designs of this type was analysed and presented to you long ago. 

That does not mean anything. Those who know very good physics may fall into the trap of not questioning something for many reasons even if there is a small doubt on their head because of an observation/experience (equals experiment), however they afraid to express it publicly over the forum. It would be like being against the stream. Unfortunately, most humans are afraid more of their reputation (especially when one is specialist on the field) than to explore something that may look initially far-fetched or ridiculous. 

Next time, take the hammer with the short leather grip (semi non-rigid) and make the experiment by yourself. I suppose there will be enough centrifugal force left in the rotating frame that will show you the way forward (enlightenment).

3 minutes ago, Ghideon said:

You are back into expecting that Newton's laws does not apply, are possible to circumvent or have "alternative interpretations". So somewhere along the line you failed to understand, point out where so we may restart at the right location. Your own example is too advanced for you at this time, you need something simplified first.

This is the simplest example I could imagine. No worries. If I am wrong then I am wrong. However, I suspect if you make a careful analysis in the rotating frame, maybe what I proposed will start to make sense. Anyway, if all other participants are of the same opinion like yours then I have nothing more to add.

Good night and be well!

Just now, Ghideon said:

Ok. Your analyse was wrong the previous time and is still wrong. 

OK. I would like to see from you (or anyone still interested) the analysis in the rotating frame. I am curious, what kind of justification we may have there.

11 minutes ago, Ghideon said:

Feel free to provide an alternative.

I already did. I am expecting no reaction upon the rest of the system while the mass m is being accelerated because the acceleration of the mass m is caused by the increasing centripetal (by subtracting the kinetic friction force). In other words, the change in centripetal appears as an inertial force in the inertial frame that by nature has no counter part (reaction force).

The same I expect to happen in the rotating frame but now with the centrifugal force that is by nature inertial having no counter part (reaction force).

13 minutes ago, Ghideon said:

the rod is pulling the mass m in radial direction 

Do you speak seriously? How can that be? The rod cannot move radially, thus cannot pull.

13 minutes ago, Ghideon said:

We can assume a negligible non-zero mass then. 

(massless does not imply zero friction)

If it helps then let us make a version with massless rod.

13 minutes ago, Ghideon said:

Yes. Is there anything else that the mass m is attached to? As long as there is non-zero friction and angular velocity w>0 the rod is pulling the mass m in radial direction 

I am not expecting to have a reaction force in this case. When we make the analysis in the rotating frame, the same conclusion is expected according to my view (in the rotating frame is clearer why there will be no reaction).

When we have to compare both analysis, either we should have a reaction or not at all, in order the observations to agree.

8 minutes ago, iNow said:

20 pages answering the same question for a person who’s being willful in his ignorance. Fascinating 

I don't think is the same question.

8 minutes ago, iNow said:

20 pages answering the same question for a person who’s being willful in his ignorance. Fascinating 

On top of page 18 we have a device. I invite you to make an analysis and give your answers to (a) and (b). Are you in?

6 minutes ago, Ghideon said:

The centripetal force is directed towards the centre, the rod accelerates the mass m. The rod is affected by an equal and opposite reaction force.

Can we assume the rod is massless?

The rod accelerate the mass m? I don't get it. I don't know where it will help if the rod is massless. But then we will have no friction.

3 minutes ago, iNow said:

20 pages answering the same question for a person who’s being willful in his ignorance. Fascinating 

You can join the conversation if you like.

8 minutes ago, Ghideon said:

If the mass is accelerating in the inertial frame of reference there is limited degrees of freedom for the direction the mass can accelerate in. It is tangential due to increased angular velocity and towards the centre due to centripetal force, OK?  

This is all well known. I am still speaking about a radial reaction force. Is there any opposing force (upon the rest of the system) to centripetal? The centripetal is the cause behind the radial acceleration of the mass m in the inertial frame. Where is the reaction upon the rest of the system?

4 minutes ago, Ghideon said:

Do you include the green forces I have added to the picture? It is the force acting in tangential direction pushing at the mass when angular velocity increase and the reaction force from the mass to the yellow rod. Since you have friction included, those forces may or may not have an impact. Again, they shouold only be present during the period of time the angular velocity is increasing

I am speaking about a radial reaction component. Is there any?

4 minutes ago, Ghideon said:

If the mass accelerates in the inertial frame of reference there is a force* acting on the mass. And therefore an equal and opposite reaction force. 

The centripetal has direction towards the rotor, right? Where the other applies?

8 minutes ago, swansont said:

It must be accelerating (the direction is changing).  Since w and r are both increasing, the tangential speed is increasing (v = wr), and there's a radial component, too. So the speed is increasing.

While accelerates radially is there a reaction force upon the rest of the system?

11 minutes ago, swansont said:

The mass slides all the way to the stop, as I said. The frictional force can't supply all of the required centripetal acceleration.

The mass slides accelerating or with constant speed?

10 minutes ago, swansont said:

And I did the inertial frame. There is no centrifugal force in the inertial frame. There are no fictitous forces, because things in inertial frames follow Newton's laws.

This is very clear, no fictitious forces for the inertial frame case. As I said, I am not comfortable with the frame of references, however Ghideon helped me to understand something (it requires more exercising from my side). Now, if you wish you have to do the non-rotating frame analysis.

10 minutes ago, swansont said:

And I did the inertial frame. There is no centrifugal force in the inertial frame. There are no fictitous forces, because things in inertial frames follow Newton's laws.

When you do the analysis in the rotating frame, it will start at rest in that frame.

I forgot to ask you what is the answer for (a) and (b) by the way for the case of the inertial frame? Will mass m accelerate or not? Will the system (M+m) accelerate in the same direction or not?

2 minutes ago, swansont said:

Either the object is rotating (inertial frame of reference) or the item is fixed and the reference frame is rotating.

Of course the object is rotating. How you are going to make the analysis has nothing to do with me. The goal/challenge is (as we agreed with Ghideon) to analyze this system from an inertial frame of reference as also from a rotating frame of reference and then to compare the results.

44 minutes ago, swansont said:

 If you increase to w2, the frictional force can't supply the required centripetal force. The mass will slide because of this.

From the moment the friction plays the role of the centripetal, before we increase the angular velocity the system is in equilibrium that means the centrifugal equals to the centripetal. Increasing the angular velocity the net force will have an outwards direction that implies centrifugal is greater than centripetal. Of course, the centripetal will increase too, however as long the angular velocity increases, the centrifugal will be greater than the centripetal. 

Moreover the centripetal has a direction towards the center of the rotor and the net force is outwards, otherwise mass m acceleration to the right cannot be justified. Additionally, the rotor is not fixed but in outer space.