John2020

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.

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?

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.

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.

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.

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

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.

Here you miss something. I will explain later.

The helix angle should be also included. It is very important, otherwise the analysis will lead to wrong conclusions. With all respect, motion occurs just along the helix (crucial detail) and not along the axis of rotation of the screw. I hope you agree with me.

What I confirmed back then I take it back because it is wrong. A couple of days ago I was studying this situation and I can say now I have a better view of how all the forces are exerted upon the nut and what is really going on. My intuition was right but just now I am able to justify how this mechanism may work. I have to update my paper this weekend in order to add all these details as forces upon the thread, and nut as also something to counteract the system countertorque in order to not rotate. My pause time is finished. See later in the evening. 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. I have to go now. I think you are right about gravity but it is not for the reason you probably think (no force along the axis of rotation). I will explain later. Yes, gravity will start pushing the nut along the helix. Here is another consideration: When you make a pure theoretical analysis (not real world application), I will be correct since then the lead must have almost zero length that will require a continues torque to apply. Go ahead. You are right with gravity but not by claiming force along the axis of rotation. See you later in the evening.

The normal forces between the thread and the nut. I am not a specialist on threads. Let's continue with what we have shared up to now.

As projecton but not as mechanism description. Here is a helping comparison: -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. If you can see clearly the difference here then I will disclose you the rest which is a little bit tricky, actually. I am almost in my workplace. See you later at the evening. See my reply to swansont, above. Nobody, said Newton is incorrect but incomplete in terms of an additional interpretation. If you take the total derivative of the change in momentum, reveals two terms, where the second one has today two interpretations (acrettion of mass, and ejection of mass). There could be a third interpretation for the same term.

The nut is not being pushed. The torque initiates its motion. Initiating its motion by the torque and then removing the torque the nut will acquire a constant speed for the frictionless horizontal scenario.

We like it or not the nut follows a helix trajectory and not a rectilinear motion. Otherwise, it is like we are addressing Fig.1-Lower (unthreaded rod and nut's rectilinear motion). This is exactly the point of misunderstanding from your part meaning that you (and not only you) ignore this very crucial detail. We have a helix trajectory in Fig.1-Upper.

Because the nut follows a helix trajectory and not a real rectilinear motion therefore it will require an initial torque. It is not the same conditions as in my construction because gravity comes into play (normally when the construction is 100% in parallel with gravity then it shouldn't be influence by it. However, in real conditions it will be difficult to be 100% in parallel in any location across the globe).

Something is missing. In order your proposal to start working as you envisioned, it will require an initial torque, otherwise it will not start to accelerate. I think we should not orientate the construction vertically because we introduce an adfitional force due to gravity (it will complicate the analysis and will lead to wrong conclusions). It would be better your construction to be placed in outer space horizontally and then to apply a couple (F_A and F_A') of non constant magnitude (increasing), permanently. That way it will start to accelerate just because of the applied torque (exactly as in my construction).

The blue box and the screw is one system, right? If so then proceed. I am not sure because we have an external field now already that of gravity (I assume you are going to introduce a nut acceleration due to earth's gravitational field). Anyway, let us see what comes next.

I am not addressing the velocity as value but the trajectory of the nut. The nut does not develop a velocity along the axis of rotation since it ascribes a helix (in our case the screw. removing the guiding bars then when you give a torque upon the nut, it will ascribe a helix, thus no axial real rectilinear velocity. Consequently, there is no real force along the axis of rotation.)

I think N1 is enough to present the argument. However, what you write about the axial component of N1 cannot apply because you assume rectilinear motion for the nut from the moment there is none (there is no rectilinear real motion along the axis of rotation). OK

You are right, my mistake. I will come on this later. In the meantime your new drawing doesn't seem to be correct. The opposing Normal forces must be collinear (N1 and N2 are not). Later in the evening. I go back to work now.

No it's not. Please check the mechanical advantage definition: https://en.wikipedia.org/wiki/Simple_machine This is the reason I used a varying angular velocity (accelerating) which is a requirement for the accelerating mass transfer that would imply in an accelerating change of the COM and eventually acceleration of the system as caused by the assumed reactionless force (fictitious in nature, it is not a rectilinear real force since it emerges through the evolution of the nut around the axis of rotation of the translation screw (when one uses your analog or my own where here the screw rotates).

I am aware about this analogy. Well this is not exactly the same as in my apparatus. The nut is being affected by a constant external gravitational force that implies constant evolution of nut around the screw that means constant displayment speed. In my case is accelerated displacement. The displacement force is not rectilinear (as we see with real contact forces) and that was the reason I called it fictitious and more accurately an artificial fictitious force because of the translation screw construction that implies an helix trajectory is at play (not rectilinear motion). However, the question remains: Where appear the normal forces pair (action-reaction) in your analogy and what is their angle in regards to the rotation axis or the evolution axis (your case).

I am saying this from the moment I shared the drawing with the thread. Furthermore, the pair appears a constant angle with the rotation axis (because of the thread inclination) while the translation screw rotates. No worries. It is perfectly understood for someone knowledgeable in Physics to use modern argumentation (see GR) in contrast to old fashioned non fascinating, boring and a closed chapter like classical mechanics. Well, from my side I explore just the possibility whether Newton's laws are incomplete (not discarded, just incomplete) or not. I would be totally careless to dismiss proven science.

Then you ignore the normal forces pair is all the time at a constant angle with the rotation axis that means they are not along the rotation axis that implies a net force that pushes the nut appears reactionless.

I cannot follow you. Do you speak about the F_A or about the normal forces pair,?