John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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? Edited October 21, 2020 by John2020
swansont Posted October 21, 2020 Posted October 21, 2020 56 minutes ago, John2020 said: 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? 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 (M+m) system would not accelerate, since there is no external force. The axis of rotation would shift by a small amount. But in the limit of M>>m this would vanish.
John2020 Posted October 21, 2020 Author Posted October 21, 2020 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?
swansont Posted October 21, 2020 Posted October 21, 2020 8 minutes ago, John2020 said: The mass slides accelerating or with constant speed? 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.
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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? Edited October 21, 2020 by John2020
Ghideon Posted October 21, 2020 Posted October 21, 2020 22 minutes ago, John2020 said: While accelerates radially is there a reaction force upon the rest of the system? 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. *) Not fictitious force.
John2020 Posted October 21, 2020 Author Posted October 21, 2020 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?
Ghideon Posted October 21, 2020 Posted October 21, 2020 1 minute ago, John2020 said: Where the other applies? I will not sidetrack @swansont's analysis and do not yet have sufficient information to give an exact answer. 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.
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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? Edited October 21, 2020 by John2020
Ghideon Posted October 21, 2020 Posted October 21, 2020 (edited) 13 minutes ago, John2020 said: I am speaking about a radial reaction component. Is there any? 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? Edited October 21, 2020 by Ghideon
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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? Edited October 21, 2020 by John2020
Ghideon Posted October 21, 2020 Posted October 21, 2020 (edited) 13 minutes ago, John2020 said: This is all well known. I am still speaking about a radial reaction force. Is there any opposing force to centripetal? 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? Edited October 21, 2020 by Ghideon
iNow Posted October 21, 2020 Posted October 21, 2020 20 pages answering the same question for a person who’s being willful in his ignorance. Fascinating
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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. Edited October 21, 2020 by John2020
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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? Edited October 21, 2020 by John2020
Ghideon Posted October 21, 2020 Posted October 21, 2020 3 minutes ago, John2020 said: The rod accelerate the mass m? 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 4 minutes ago, John2020 said: I don't know where it will help if the rod is massless. But then we will have no friction. We can assume a negligible non-zero mass then. (massless does not imply zero friction) 3 minutes ago, iNow said: Fascinating There are only six threads with more answers in the speculations section. I'm aiming for the record.
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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. Edited October 21, 2020 by John2020
Ghideon Posted October 21, 2020 Posted October 21, 2020 (edited) 19 minutes ago, John2020 said: Do you speak seriously? How can that be? The rod cannot move radially, thus cannot pull. I am serious but maybe use incorrect words. As seen from an inertial frame of reference the mass m is at all times in centripetal acceleration. Acceleration means force, F=ma. In the inertial frame of reference mass m is never at rest, mass m is never moving with constant velocity, mass m is accelerating towards the centre of the circle. The rod has friction so the mass m can't slide free along the rod, the friction slows down any radial movement along the rod. That friction means that the rod is, at all times, able to affect the mass m with a centripetal force. The force is not constant but you have not stated anything saying the force can be zero. Under those circumstances the rod is the object that applies the force that accelerates mass m. Feel free to provide an alternative. Edited October 21, 2020 by Ghideon
John2020 Posted October 21, 2020 Author Posted October 21, 2020 (edited) 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). Edited October 21, 2020 by John2020
Ghideon Posted October 21, 2020 Posted October 21, 2020 (edited) 20 minutes ago, John2020 said: 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). Ok. Your analyse was wrong the previous time and is still wrong. Edited October 21, 2020 by Ghideon
John2020 Posted October 21, 2020 Author Posted October 21, 2020 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.
Ghideon Posted October 21, 2020 Posted October 21, 2020 22 minutes ago, John2020 said: 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. It looks like you have misunderstood my explanation of the simple example* I posted; your analysis is not compatible with Newtons laws. Doing an analysis of the rotating frame is of limited value at this. 45 minutes ago, John2020 said: 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). I had some hopes that you had grasped the basics by now. For instance: Centripetal force is not an inertial force. So there is no way forward from here, we need to go back for a while: 5 hours ago, Ghideon said: Then you realise that Newton holds, there is no room fo any "interpretation" or circumventing. We apply the correct laws to your example and check the outcome. Ok? You said** 5 hours ago, John2020 said: OK! 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. *) Constant angular velocity, two frames of reference **) https://www.scienceforums.net/topic/123261-circumventing-newtons-third-law-through-euler-inertial-forces/?do=findComment&comment=1157186
John2020 Posted October 21, 2020 Author Posted October 21, 2020 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!
Ghideon Posted October 21, 2020 Posted October 21, 2020 (edited) Does your answer imply that you are not prepared to move back to basics and try again? 24 minutes ago, John2020 said: This is the simplest example I could imagine 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. 24 minutes ago, John2020 said: No worries. If I am wrong then I am wrong. 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. 24 minutes ago, John2020 said: However, I suspect if you make a careful analysis in the rotating frame, maybe what I proposed will start to make sense. 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. 24 minutes ago, John2020 said: Anyway, if all other participants are of the same opinion like yours then I have nothing more to add. 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. *) (Thats what you are implying to someone who know some physics) Edited October 21, 2020 by Ghideon 1
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