joigus Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 9:50 AM, John2020 said: Here you miss something. I will explain later. Expand I'm always open to surprises. Your new concept of space distorted by a nut and screw I can only eagerly await. Get ready for some heavy-duty vector algebra and some real analysis too. And by real I mean... Get ready to get real. Pun intended.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 On 10/15/2020 at 9:59 AM, joigus said: I'm always open to surprises. Your new concept of space distorted by a nut and screw I can only eagerly await. Expand First of all, I would like to correct your statement "relative linear displacement" to "relative fictitious linear displacement". Reasoning: a) There is no real force along the axis of rotation. b) The nut follows a helix trajectory because of the threaded rod. c) The analysis has to be done while the nut (and the thread in opposite rotation direction) moves along the helix trajectory. Maybe, later in the evening I may share a complete diagram with all the forces (friction, normal and torque) that act upon the nut and the thread and what is really going on with this construction (how the COM accelerates). A short answer (Hint) on the above is: While the screw rotates clockwise (see helix trajectory), it induces a counterclockwise motion (see helix trajectory in opposite direction) upon the nut. The key to understand why all analysis fail (I mean conclude the opposite of what I expect) is the following: 1.Motion is allowed only over the helix trajectory. Otherwise, it automatically introduces the action-reaction principle for collinear forces that leads to misunderstanding/failure. 2.The moment the nut advances counterclockwise that is translated to fictitious displacement (means not caused by a real linear force), the screw turns clockwise (along the helix), however without being able (see linear actuator topology. The screw is hold by the housings (being in the two ends of the screw)) to transfer mass (as it happens with the nut) in the other direction. 3.Due to (1) and (2) we have an accelerated mass transfer without causing a reaction upon the rest of the system that leads to the change and acceleration of COM of the system as a whole. Important Note: Attempting to do the same using a nut linear motion (real force) the analysis becomes what we have in Fig.1-Lower (which there, although the COM changes, it cannot be accelerated due to Newton's 3rd law.
Ghideon Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 7:42 AM, John2020 said: What I confirmed back then I take it back because it is wrong. Expand Ok, you claim the velocity is constant again. On 10/15/2020 at 7:42 AM, John2020 said: Yes, gravity will start pushing the nut along the helix. Expand At time t=0 the velocity v=0. at some time later t>0 we have v>0. That is not constant velocity. The statements contradict each other, please clarify. On 10/15/2020 at 7:42 AM, John2020 said: No. In the case of the ball, gravity exerts a force rectilinear, where just the component along the hill will affect and start directly the ball motion without push. It is not the same situation with the translation screw. Expand Ok. So a ball placed on a straight slope will start roling downhill due to gravity. I get that the helix shape is important. Will a ball placed in a helix shaped slide remain at rest until pushed? I'm continuing this line of reasoning to allow for possible simplifications; that will allow us to find the specific difference between an object that needs an initial torque vs one that will start to move due to gravity, without an initial external "push" or torque. Finding a simple object or device makes it easier to draw the forces and make a analyse.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 You are right about gravity. In all frictionless cases you will need no torque to initiate since gravity play this role, although I have to make a drawing to demonstrate this. Please check my post above quoting joigus and tell me what you think. Important: Again, no linear motion along the axis of rotation. See you later in the evening
swansont Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 5:50 AM, John2020 said: As projecton but not as mechanism description. Here is a helping comparison: Expand As physics analysis, where terms have specific meanings Quote -Cranksaft: Converts linear to rotational motion and vice versa through real forces. Here your analysis would be correct -Leadscrew with nut: Converts rotational motion (real force) to mass transfer (Inertial force). No real force is pushing along the axis since there is none. However, there is a real force that pushes the nut along the helix trajectory. Expand Those are descriptions, not physics analysis. There is a force; I’ve identified it. All you have done is assert the contrary and avoid actual discussion of the force vector components. If there is no net axial force, what is balancing the axial component of the normal force of the bolt on the nut? If something moves along any line or curve, it has a linear speed. If it rotates on or revolves about an axis it has an angular speed. (and if it moves it has momentum. Both linear and angular) Quote If you can see clearly the difference here then I will disclose you the rest which is a little bit tricky, actually. Expand You are not in a position to disclose any physics insight. On 10/15/2020 at 7:28 AM, John2020 said: The normal forces between the thread and the nut. Expand Show this with a free-body diagram and component analysis. On 10/15/2020 at 10:45 AM, John2020 said: First of all, I would like to correct your statement "relative linear displacement" to "relative fictitious linear displacement". Reasoning: a) There is no real force along the axis of rotation. Expand Wrong. Nothing valid follows from an incorrect premise, and it’s pointless to discuss anything beyond this, since it will be wrong On 10/15/2020 at 11:01 AM, John2020 said: You are right about gravity. In all frictionless cases you will need no torque to initiate since gravity play this role, although I have to make a drawing to demonstrate this. Please check my post above quoting joigus and tell me what you think. Important: Again, no linear motion along the axis of rotation. See you later in the evening Expand No linear motion? How does it get to the bottom? How does it rotate without its center of mass moving? If the CoM moves, there is linear motion.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 (edited) On 10/15/2020 at 11:08 AM, swansont said: Wrong. Nothing valid follows from an incorrect premise, and it’s pointless to discuss anything beyond this, since it will be wrong Expand No it is not wrong. I insist motion occurs only along the helix trajectory. When you finish the analysis with the helix then, you see how affects the motion of the entire system along the axis of rotation. I can do it but later in the evening or in the weekend. I have no time actually. Or let us see your version first or anyone who would like to do the analysis when he agrees with my justification above. Note: I removed what I wrote with xx' axis. It was wrong what I wrote. Edited October 15, 2020 by John2020
joigus Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 11:20 AM, John2020 said: No it is not wrong. Do you know way? Because you place the xx' axis along the rotation axis that leads to false analysis. I insist motion occurs only along the helix trajectory (here you have to place the xx' axis to start your analysis). When you finish the analysis with the helix then, you see how affects the motion of the entire system along the axis of rotation. Expand I'm starting to suspect you don't understand how a nut works. It does not follow an helical trajectory. A point at the contact surface does, not the nut as a whole. For every point that moves in that helical orbit, a symmetrical point moves opposite to it, and the nut advances along the axis. No "overall helical motion" results. Is that what you don't see?
John2020 Posted October 15, 2020 Author Posted October 15, 2020 (edited) On 10/15/2020 at 11:26 AM, joigus said: Is that what you don't see? Expand Remove the guiding bars and give a torque to the nut. Will it follow a helix trajectory or not? I understand what you mean. The contacts follow the helix trajectory that means the motion of the nut should be attributed to a helix and not to linear motion. Otherwise, you conclude wrong. Make the following exercise: Remove the guiding bars, keep the screw fixed (not rotating) and assume the applied torque to the nut now will be converted to nut displacement. We are speaking exactly about the same thing. I have to go back to work. Edited October 15, 2020 by John2020
joigus Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 11:37 AM, John2020 said: Remove the guiding bars and give a torque to the nut. Will it follow a helix trajectory or not? Expand That's easy: No.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 After recognizing the above crucial detail that all of you missed and overlooked, the discussion will start from now and on to become really interesting. On 10/15/2020 at 12:56 PM, joigus said: That's easy: No. Expand If you really mean it then the discussion is over.
joigus Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 12:57 PM, John2020 said: After recognizing the above crucial detail that all of you missed and overlooked, the discussion will start from now and on to become really interesting. If you really mean it then the discussion is over. Expand You're not the one who gets to say when the discussion is over, may I point out.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 Use the below: Make the following exercise: Remove the guiding bars, keep the screw fixed (not rotating) and assume the applied torque to the nut now will be converted to nut displacement. We are speaking exactly about the same thing. Do you still answer with a No?
joigus Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 1:01 PM, John2020 said: Do you still answer with a No? Expand Yes.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 If your answer and all the participants is a NO then, I don't think we have to discuss anything else and I would ask from the Moderator to close this thread.
Ghideon Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 11:01 AM, John2020 said: You are right about gravity. In all frictionless cases you will need no torque to initiate since gravity play this role, although I have to make a drawing to demonstrate this. Expand Just to make sure you do not still claim constant velocity. The object will accelerate due to the gravity. Yes? On 10/15/2020 at 11:01 AM, John2020 said: Please check my post above quoting joigus and tell me what you think. Expand OK! (Unless later posts makes it unnecessary) On 10/15/2020 at 11:01 AM, John2020 said: Important: Again, no linear motion along the axis of rotation. Expand I do not agree. But thanks for the notice, this is an important thing to analyse; finding the exact reason for that statement. We may continue later.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 Dear @Phi for All I am asking you to close this thread since it has served its purpose and thank you very much so far for your understanding and patience.
joigus Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 1:18 PM, Ghideon said: Just to make sure you do not still claim constant velocity. The object will accelerate due to the gravity. Yes? Expand Wait a minute. Has the claim changed again? If there is gravity, the nature of the claim changes completely. That's not what I understood.
Ghideon Posted October 15, 2020 Posted October 15, 2020 (edited) On 10/15/2020 at 1:20 PM, joigus said: Wait a minute. Has the claim changed again? Expand Due to the latest information I have available the answer is yes. Off Topic and less serious: On 10/15/2020 at 11:26 AM, joigus said: nut works Expand English is not my fist language but I think I prefer a bag of Nutworks rather than explaining how a nut works to nut jobs. On 10/15/2020 at 1:20 PM, John2020 said: I am asking you to close this thread since it has served its purpose and thank you very much so far for your understanding and patience. Expand Thanks for noticing. Just curious, this means you found the error(s) in your approach? Edited October 15, 2020 by Ghideon 1
swansont Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 11:20 AM, John2020 said: No it is not wrong. I insist motion occurs only along the helix trajectory. Expand Insist all you want. It’s wrong. Whatever you’re doing, it’s not physics. Roll a cylinder down an inclined plane. If you don’t account for linear motion (translational KE) you will get the wrong answer. Good luck with convincing the world that energy conservation isn’t a thing Also, “follow a helix trajectory” is inaccurate. The CoM doesn’t do this, which is what a trajectory refers to. The object is rotating and translating. You need to use proper terminology. It’s bad enough you’re making physics up.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 (edited) On 10/15/2020 at 1:28 PM, Ghideon said: Thanks for noticing. Just curious, this means you found the error(s) in your approach? Expand Yes, I found it and is the following: Those who participate in this discussion think they know better by ignoring of what they see (along with the thread writer(me)) in favor of what is familiar to them and to their company. This has as result to confuse parts of the discussion, eirher on purpose or because they don't follow the discussion (see joigus last question about gravity. This has to do with Ghideon thought experiment and not with my construction). On 10/15/2020 at 2:25 PM, swansont said: Insist all you want. It’s wrong. Whatever you’re doing, it’s not physics. Expand You still don't see where you (all of you) are wrong. Does the helix trajectory has intrinsically what you call linear motion? Otherwise, it would be called just a circle. Edited October 15, 2020 by John2020
swansont Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 2:36 PM, John2020 said: You still don't see where you (all of you) are wrong. Expand If you’re going to argue with the teachers you at least need to provide a credible reference to back up your claim. You have no credibility for your assertions. 4 minutes ago, John2020 said: Does the helix trajectory has intrinsically what you call linear motion? Otherwise, it would be called a circle. Expand It’s not a helix trajectory. A charged particle in a magnetic field can exhibit a helix trajectory (but let’s not go there. We have enough misconceptions already) The nut in free space, spinning on its axis would be rotation without translation. The CoM doesn’t go anywhere.
Ghideon Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 2:36 PM, John2020 said: Yes, I found it and is the following: Those who participate in this discussion think they know better by ignoring of what they see (along with the thread writer(me)) in favor of what is familiar to them and to their company. This has as result to confuse parts of the discussion, eirher on purpose or because they don't follow the discussion (see joigus last question about gravity. This has to do with Ghideon thought experiment and not with my construction). Expand Sorry if my thought experiments moved the discussion in an unwanted direction and allowed for confusion.
John2020 Posted October 15, 2020 Author Posted October 15, 2020 Let us see again my argument in the construction in Fig.1-Upper: a) Remove the guiding bars, keep the screw fixed (not rotating). Apply a torque upon the nut and assume it will be converted to nut displacement (fictitious = not over a linear force). b) See my construction. There instead the space (screw) rotates and the contacts of the nut ascribe a helix that results in an induced motion of the nut that is essentially based on an helical trajectory.
swansont Posted October 15, 2020 Posted October 15, 2020 On 10/15/2020 at 2:50 PM, John2020 said: Let us see again my argument in the construction in Fig.1-Upper: a) Remove the guiding bars, keep the screw fixed (not rotating). Apply a torque upon the nut and assume it will be converted to nut displacement (fictitious = not over a linear force). Expand Your argument is flawed because nothing about this scenario is fictitious. if you apply a tourque to the nut it will rotate and translate, and with increasing speed as long as the torque is applied. Further, you would have to account for both translational and angular momentum and energy to get the right answer. Quote b) See my construction. There instead the space (screw) rotates and the contacts of the nut ascribe a helix that results in an induced motion of the nut that is essentially based on an helical trajectory. Expand Trajectory refers to the CoM motion. It is not helical. Stop making stuff up.
Ghideon Posted October 15, 2020 Posted October 15, 2020 (edited) On 10/15/2020 at 2:50 PM, John2020 said: Let us see again my argument in the construction in Fig.1-Upper: Expand Not yet. I'm not moving away from the vertical case. On 10/15/2020 at 11:01 AM, John2020 said: You are right about gravity. In all frictionless cases you will need no torque to initiate since gravity play this role, although I have to make a drawing to demonstrate this. Expand Just to make sure you do not still claim constant velocity. The object will accelerate due to the gravity. Yes? On 10/15/2020 at 11:01 AM, John2020 said: Important: Again, no linear motion along the axis of rotation. Expand 1: What is your definition of linear motion? 2: What is your definition of helical motion? Edited October 15, 2020 by Ghideon added 2:nd question
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