John2020 Posted May 22, 2021 Posted May 22, 2021 Hi everybody! I would like to share three experiments I conducted some 11 years ago as also I may share all the technical details in case there is interest to make some calculations: url deleted per rule 2.7 I am searching for an answer in the following questions: a) Since there are no external forces pushing the ferromagnetic ring in any direction in all three videos then, how does it move? b) if (a) is correct then, what Newton's 3rd law has to say about it?
exchemist Posted May 22, 2021 Posted May 22, 2021 14 minutes ago, John2020 said: Hi everybody! I would like to share three experiments I conducted some 11 years ago as also I may share all the technical details in case there is interest to make some calculations: I am searching for an answer in the following questions: a) Since there are no external forces pushing the ferromagnetic ring in any direction in all three videos then, how does it move? b) if (a) is correct then, what Newton's 3rd law has to say about it? If you can explain your concept in words, with a diagram, we can have a look and see where your analysis is faulty. But videos are a waste of time for that sort of thing, as it is impossible to tell exactly what one is looking at, how it is powered and so forth. They also have the great disadvantage of being a linear medium, so you have to keep rewinding to see again anything you need to revisit. So give us a summary in words, please, if you want help with this.
swansont Posted May 22, 2021 Posted May 22, 2021 14 minutes ago, John2020 said: Hi everybody! I would like to share three experiments I conducted some 11 years ago as also I may share all the technical details in case there is interest to make some calculations: ! Moderator Note Which is against the rules. You must post the material for discussion here. You can’t require anyone to watch a video or click on a link to participate
John2020 Posted May 22, 2021 Author Posted May 22, 2021 OK, I will present the setup with some technical details to help the members understand what is all about. The setup consists of an L-R circuit in series: -Inductance: L = 1mH -> (Ferromagnetic ring as core) -Resistance: R = 4.7 Ohm (High Power Resistor) -Driving Frequency approx. 5 KHz -Current: approx. 0.6A Exp #1: Self-propelled moving ferromagnetic ring. Here we have a special situation like a self-frequency shift. Generator's frequency is kept unchanged. Exp #2: Self-propelled LEGO car (pushing a LEGO car from inside). AM Modulation using a 200mHz (milliHerz) wave as message signal. Exp #3: Self-propelled rotating ferromagnetic ring. Manual frequency shift through the Generator that leads to controlling the rotation direction of the ring. Experiments: https://www.youtube.com/channel/UCyHiYTj88O2ylGEXcq3am4w I am searching for an answer in the following questions: a) Since there are no external forces pushing the ferromagnetic ring in any direction in all three videos then, how does it move? b) if (a) is correct then, what Newton's 3rd law has to say about it?
exchemist Posted May 22, 2021 Posted May 22, 2021 34 minutes ago, John2020 said: OK, I will present the setup with some technical details to help the members understand what is all about. The setup consists of an L-R circuit in series: -Inductance: L = 1mH -> (Ferromagnetic ring as core) -Resistance: R = 4.7 Ohm (High Power Resistor) -Driving Frequency approx. 5 KHz -Current: approx. 0.6A Exp #1: Self-propelled moving ferromagnetic ring. Here we have a special situation like a self-frequency shift. Generator's frequency is kept unchanged. Exp #2: Self-propelled LEGO car (pushing a LEGO car from inside). AM Modulation using a 200mHz (milliHerz) wave as message signal. Exp #3: Self-propelled rotating ferromagnetic ring. Manual frequency shift through the Generator that leads to controlling the rotation direction of the ring. Experiments: https://www.youtube.com/channel/UCyHiYTj88O2ylGEXcq3am4w I am searching for an answer in the following questions: a) Since there are no external forces pushing the ferromagnetic ring in any direction in all three videos then, how does it move? b) if (a) is correct then, what Newton's 3rd law has to say about it? From your description all I see is a circuit with a resistance and an inductance, with a high frequency AC current flowing in it. As you have not described the physical arrangement of the components, it is impossible to comment on whether any motion of any part would be expected.
John2020 Posted May 22, 2021 Author Posted May 22, 2021 (edited) 8 minutes ago, exchemist said: From your description all I see is a circuit with a resistance and an inductance, with a high frequency AC current flowing in it. As you have not described the physical arrangement of the components, it is impossible to comment on whether any motion of any part would be expected. The physical arrangement of the components is clearly seen in Exp #1 and Exp #3. The same arrangement applies to Exp #2. In other words, we have a coil with a ferromagnetic ring as core that has a mass of 0.2 Kgr being electrically connected in series with the 4.7 Ohm resistor (not moving). After powering the L-R circuit, the only component that unexpectedly moves by itself in the setup is just the coil in all three experiments (Exp #1, Exp #2 and Exp #3). Edited May 22, 2021 by John2020
exchemist Posted May 22, 2021 Posted May 22, 2021 (edited) 7 minutes ago, John2020 said: The physical arrangement of the components is clearly seen in Exp #1 and Exp #3. The same arrangement applies to Exp #2. In other words, we have a coil with a ferromagnetic ring as core that has a mass of 0.2 Kgr being electrically connected in series with the 4.7 Ohm resistor (not moving). After powering the L-R circuit, the only component that unexpectedly moves by itself in the setup is just the coil in all three experiments (Exp #1, Exp #2 and Exp #3). OK. So you have a high frequency alternating magnetic field in this ferrite ring, and when you energise it you find the ring slowly slides across the table. I notice the table has metal legs and that there are various large metal components also on the table. It is unclear whether or not the table is flat. I have two questions for you. First, if you hold the ring in your hand, do you feel any vibration, or when it is on the table, can you hear any sound from it? Second, what happens when you place the ring on a surface with no metal objects nearby? Edited May 22, 2021 by exchemist
John2020 Posted May 22, 2021 Author Posted May 22, 2021 6 minutes ago, exchemist said: OK. So you have a high frequency alternating magnetic field in this ferrite ring, and when you energise it you find the ring slowly slides across the table. I notice the table has metal legs and that there are various large metal components also on the table. It is unclear whether or not the table is flat. I have two questions for you. First, if you hold the ring in your hand, do you feel any vibration, or when it is on the table, can you hear any sound from it? Second, what happens when you place the ring on a surface with no metal objects nearby? About your questions: -We speak about the MnZn (Manganese Zinc alloy) ferromagnetic core named T87/56/13 3E6 Grade. See technical details below: -The ring core data as also the topology of the ring itself will practically keep all magnetic field lines inside the core. Therefore, the table metal legs and other components will not affect its behavior. -The table is flat. -The ring creates a very loud sound as you may have already noticed by watching the videos. -I never hold it in my hands. -When I first witnessed this phenomenon the ring was placed on the floor away from any metal objects and had a similar behavior. Take into consideration that any change in the current affects the electromagnetic characteristics of the core, namely the magnetic permeability. See B-H Curve below:
exchemist Posted May 22, 2021 Posted May 22, 2021 (edited) 56 minutes ago, John2020 said: About your questions: -We speak about the MnZn (Manganese Zinc alloy) ferromagnetic core named T87/56/13 3E6 Grade. See technical details below: -The ring core data as also the topology of the ring itself will practically keep all magnetic field lines inside the core. Therefore, the table metal legs and other components will not affect its behavior. -The table is flat. -The ring creates a very loud sound as you may have already noticed by watching the videos. -I never hold it in my hands. -When I first witnessed this phenomenon the ring was placed on the floor away from any metal objects and had a similar behavior. Take into consideration that any change in the current affects the electromagnetic characteristics of the core, namely the magnetic permeability. See B-H Curve below: OK if it makes a loud sound it is vibrating. This will make it tend to move if there is any asymmetry in its contact with the surface it rests on, or if there is any force from strain in the the wires. It will also make it move more readily in response to gravity, if there is any slope at all in the surface it is resting on. Coils actually expand and contract in synch with the current flow. You have a conductor in a magnetic field, so it will experience a force at right angles to both, by Fleming's Left Hand Rule, which stretches and then relaxes the coil. So it will vibrate. (Electric motor armatures have to be very tightly wound for this reason - to stop the windings coming loose when energised as the windings stretch.) I think this vibration may be the source of the motion. Edited May 22, 2021 by exchemist
swansont Posted May 22, 2021 Posted May 22, 2021 2 hours ago, John2020 said: OK, I will present the setup with some technical details to help the members understand what is all about. The setup consists of an L-R circuit in series: -Inductance: L = 1mH -> (Ferromagnetic ring as core) -Resistance: R = 4.7 Ohm (High Power Resistor) -Driving Frequency approx. 5 KHz -Current: approx. 0.6A Exp #1: Self-propelled moving ferromagnetic ring. Here we have a special situation like a self-frequency shift. Generator's frequency is kept unchanged. Exp #2: Self-propelled LEGO car (pushing a LEGO car from inside). AM Modulation using a 200mHz (milliHerz) wave as message signal. Exp #3: Self-propelled rotating ferromagnetic ring. Manual frequency shift through the Generator that leads to controlling the rotation direction of the ring. Experiments: I am searching for an answer in the following questions: a) Since there are no external forces pushing the ferromagnetic ring in any direction in all three videos then, how does it move? b) if (a) is correct then, what Newton's 3rd law has to say about it? ! Moderator Note Is there a comprehension problem here? members should be able to participate in the discussion without clicking any links or watching any videos
John2020 Posted May 22, 2021 Author Posted May 22, 2021 1 minute ago, swansont said: Is there a comprehension problem here? members should be able to participate in the discussion without clicking any links or watching any videos No there is not. I placed a description and the experimental results (the link with the video). Where is the problem? Without the experiments the discussion is useless. As you already have noticed the exchemist already participates in the discussion and has already raised some questions.
swansont Posted May 22, 2021 Posted May 22, 2021 A ferrite core with an AC current creates a magnetic field, which will interact with nearby fields from current-carrying wires. Also magnetic materials. I imagine there are wires. There’s also the phenomenon of magnetostriction https://en.wikipedia.org/wiki/Magnetostriction Without watching the video I can’t tell if this might be happening. Any noise coming from the core? edit to add: https://res.mdpi.com/d_attachment/materials/materials-11-01894/article_deploy/materials-11-01894.pdf Magnetostrictive strain is the main source of acoustic noise generated by transformers If it makes sound, it’s vibrating. 7 minutes ago, John2020 said: As you already have noticed the exchemist already participates in the discussion and has already raised some questions. I don’t know if they watched any videos
John2020 Posted May 22, 2021 Author Posted May 22, 2021 4 minutes ago, swansont said: Without watching the video I can’t tell if this might be happening. Any noise coming from the core? Yes, there is a noise coming from the core. However, if you could have let the videos been watched by the members you would have noticed (Exp #3) there is one where the rotation of the core is controllable by shifting the frequency manually. Consequently, magnetostriction is half the answer. 4 minutes ago, swansont said: I don’t know if they watched any videos What is the problem to discuss the subject by having additionally some experimental results made by the initiator (me)of this thread? I will place the link to the videos in my signature. I hope you will not close the thread because of this. -1
swansont Posted May 22, 2021 Posted May 22, 2021 2 minutes ago, John2020 said: Yes, there is a noise coming from the core. However, if you could have let the videos been watched by the members you would have noticed (Exp #3) there is one where the rotation of the core is controllable by shifting the frequency manually. Consequently, magnetostriction is half the answer. “let the videos been watched by the members“ is a misrepresentation of the rules. Which indicates a comprehension problem. 4 minutes ago, John2020 said: I will place the link to the videos in my signature. ! Moderator Note No, you will not.
John2020 Posted May 22, 2021 Author Posted May 22, 2021 1 minute ago, swansont said: “let the videos been watched by the members“ is a misrepresentation of the rules. Which indicates a comprehension problem. How one could show to someone else a phenomenon that requires some explanation? Just by writing. Who is going to believe it? None. And because of this you would be happy to close the thread by judging the person who opened that thread does not understand physics. Well, maybe I don't understand physics so well, however this doesn't forbid me to think and to raise questions. So, here there is a chance to discuss a subject by having some kind of evidence. Just by throwing the words "vibrations" and "magnetostriction" cannot justify the motion of the core across the table or the LEGO car motion or the controllable rotation. Allow me to share the Link to the experiments in order for anyone to have a decent point of view. In the About me section of my Profile I have the link to the Experiments. swansont, if you close the thread because of this, it will automatically prove the mods act in the name of discrimination and dishonesty. It is your call. 1 hour ago, exchemist said: I think this vibration may be the source of the motion. Well this is the usual answer most people give, however they cannot justify why the ring should move from the moment there are no external excitation forces at play (horizontal plane). By claiming the vibration is the solution to the puzzle, it cannot justify the motion itself (see Newton's 3rd law in the context of internal forces). Anyway, it is not in my intentions to go back to the arguments regarding the rotating unbalance thread which in a way these experiments are associated to. Whoever I showed those experiments they claimed the same unjustified vibrations (see Newton's 3rd law in the context of internal forces), however none (I don't understand why) of them address the video with the LEGO car. The ring is placed on the back of the LEGO car which is the only component that could be blamed pushing the LEGO car forwards. Consequently, according to Newton's 3rd law the LEGO car should never move, however and unexpectedly it moves. -2
exchemist Posted May 22, 2021 Posted May 22, 2021 32 minutes ago, John2020 said: How one could show to someone else a phenomenon that requires some explanation? Just by writing. Who is going to believe it? None. And because of this you would be happy to close the thread by judging the person who opened that thread does not understand physics. Well, maybe I don't understand physics so well, however this doesn't forbid me to think and to raise questions. So, here there is a chance to discuss a subject by having some kind of evidence. Just by throwing the words "vibrations" and "magnetostriction" cannot justify the motion of the core across the table or the LEGO car motion or the controllable rotation. Allow me to share the Link to the experiments in order for anyone to have a decent point of view. In the About me section of my Profile I have the link to the Experiments. swansont, if you close the thread because of this, it will automatically prove the mods act in the name of discrimination and dishonesty. It is your call. Well this is the usual answer most people give, however they cannot justify why the ring should move from the moment there are no external excitation forces at play (horizontal plane). By claiming the vibration is the solution to the puzzle, it cannot justify the motion itself (see Newton's 3rd law in the context of internal forces). Anyway, it is not in my intentions to go back to the arguments regarding the rotating unbalance thread which in a way these experiments are associated to. Whoever I showed those experiments they claimed the same unjustified vibrations (see Newton's 3rd law in the context of internal forces), however none (I don't understand why) of them address the video with the LEGO car. The ring is placed on the back of the LEGO car which is the only component that could be blamed pushing the LEGO car forwards. Consequently, according to Newton's 3rd law the LEGO car should never move, however and unexpectedly it moves. There is no connection to your eccentric mass (washing machine - type) example whatsoever and I find it depressing that you have still failed to grasp how to analyse that example. It is commonplace for vibrating devices placed on nominally horizontal surfaces to move. The object is in effect jumping off the surface many times per second, so any tiny source of asymmetry of forces in the contact zone can cause it to move. This is why kitchen appliances like my blender have suction feet on them. Forget this crank nonsense about Newton's laws being broken.
John2020 Posted May 22, 2021 Author Posted May 22, 2021 2 minutes ago, exchemist said: There is no connection to your eccentric mass (washing machine - type) example whatsoever and I find it depressing that you have still failed to grasp how to analyse that example. It is commonplace for vibrating devices placed on nominally horizontal surfaces to move. The object is in effect jumping off the surface many times per second, so any tiny source of asymmetry of forces in the contact zone can cause it to move. This is why kitchen appliances like my blender have suction feet on them. Forget this crank nonsense about Newton's laws being broken. It is clear that you cannot explain why a device should vibrate in the context of Newton's 3rd law regarding just internal forces. There is an apparent difference between a rotating unbalance and a vibrating spring with a mass attached. Anyway, I am not going to continue the discussion about the eccentric mass, the current thread has a different subject. So, forget about it and just focus on the questions below: a) Why a solid mass like the ring, having no moving parts, should start moving as seen on that video? b) Why the LEGO car starts moving from the moment the ring is on its back? Could anyone push his car while being inside? Definitely, not! c) Why the rotating ring moves with a 100% controllable rotating direction just by applying a frequency shift (increased frequency -> turns clockwise, decreasing frequency -> turns counterclockwise)? The main question is: Since there are no excitation external forces, how the ring moves? Newton's 3rd law forbids motion by means of internal forces. -1
exchemist Posted May 22, 2021 Posted May 22, 2021 (edited) 2 hours ago, John2020 said: It is clear that you cannot explain why a device should vibrate in the context of Newton's 3rd law regarding just internal forces. There is an apparent difference between a rotating unbalance and a vibrating spring with a mass attached. Anyway, I am not going to continue the discussion about the eccentric mass, the current thread has a different subject. So, forget about it and just focus on the questions below: a) Why a solid mass like the ring, having no moving parts, should start moving as seen on that video? b) Why the LEGO car starts moving from the moment the ring is on its back? Could anyone push his car while being inside? Definitely, not! c) Why the rotating ring moves with a 100% controllable rotating direction just by applying a frequency shift (increased frequency -> turns clockwise, decreasing frequency -> turns counterclockwise)? The main question is: Since there are no excitation external forces, how the ring moves? Newton's 3rd law forbids motion by means of internal forces. I explained the vibration of your washing machine twice, but you ignored it, just demanding all over again that we provide an explanation. Both I and @swansont have explained why your ferrite ring vibrates, and I have explained, twice, why that can lead to motion. But you have ignored it and now you are demanding all over again that we explain it. In neither case has there been any engagement from you with what we have had to say. If you will not even address our explanations, what is there for us to do? Repeat ourselves? As for Newton's laws, I will tell you, one last time, that Newton's laws require only that the centre of gravity of an object continues in a straight line at constant speed if no net force acts. If it is non-rigid, and part of it is in motion relative to the CG, then Newton's laws demand that there be a correspondong motion elsewhere, to maintain the CG moving in this way. As I told you before, gas molecules, floating in free space between collisions, vibrate. This is entirely in accordance with Newton's laws. You have got this wrong notion from somewhere that a non-rigid body, free from external forces, can't be in a state of vibration. That is just ballocks, I'm afraid. Edited May 22, 2021 by exchemist 1
swansont Posted May 22, 2021 Posted May 22, 2021 3 hours ago, John2020 said: How one could show to someone else a phenomenon that requires some explanation? You can upload pictures, which are displayed in the thread. You can include a full description of the setup. Quote Well, maybe I don't understand physics so well, however this doesn't forbid me to think and to raise questions. But you aren’t. You are insisting you have an explanation, which violates Newton’s laws Quote swansont, if you close the thread because of this, it will automatically prove the mods act in the name of discrimination and dishonesty. It is your call. If I (or another mod) close the thread, and/or if you are suspended, it will be because you refused to follow our rules, and that’s all on you, regardless of how much you invoke a persecution complex and blame others. Quote Well this is the usual answer most people give, however they cannot justify why the ring should move from the moment there are no external excitation forces at play (horizontal plane). By claiming the vibration is the solution to the puzzle, it cannot justify the motion itself (see Newton's 3rd law in the context of internal forces). It’s in contact with the table, which means there are external forces. 2 hours ago, John2020 said: It is clear that you cannot explain why a device should vibrate in the context of Newton's 3rd law regarding just internal forces. Because this doesn’t apply. 2 hours ago, John2020 said: Why a solid mass like the ring, having no moving parts, should start moving as seen on that video? Magnetostriction means this is an incredibly bad assumption. 2 hours ago, John2020 said: The main question is: Since there are no excitation external forces, how the ring moves? The table exerts an external force, so this is moot. 1
John2020 Posted May 22, 2021 Author Posted May 22, 2021 (edited) 1 hour ago, swansont said: You can upload pictures, which are displayed in the thread. You can include a full description of the setup. When motion is involved, pictures are useless. It requires videos instead. 1 hour ago, swansont said: But you aren’t. You are insisting you have an explanation, which violates Newton’s laws I am asking you how you explain and not how I see it. However, you still ignore Newton's 3rd law for an isolated system. 1 hour ago, swansont said: If I (or another mod) close the thread, and/or if you are suspended, it will be because you refused to follow our rules, and that’s all on you, regardless of how much you invoke a persecution complex and blame others. Do whatever you like, I don't care. 1 hour ago, swansont said: It’s in contact with the table, which means there are external forces. Contact forces are supporting and not excitation forces. 1 hour ago, swansont said: Because this doesn’t apply. You are forcing me to refer to the rotating unbalance for once more. Since you are good at maths (and not only you), if you check the second order inhomogeneous differential equation and its particular solution, you will realize as the differential equation as also its solution, may justify only the response of the system. In terms of physics, it fails to justify the cause of the effect of vibration of the isolated system itself (no external excitation forces, no gravity, nothing) since there are only internal forces at play. If you do not agree with the above statement then, you cannot clearly identify all parts of the differential equation. I just found quickly an image from internet showing the differential equation. See below: Could you show me the excitation force on the above differential equation? Isn't just the RHS of the equation or not? Now in order to simplify the above system, set the stiffness (k) and the damping coefficient (c) to zero. What remains? Note: Gravity is not taking into account (see differential equation) therefore the system is isolated. It means the system vibrates in absence of external forces. 1 hour ago, exchemist said: I explained the vibration of your washing machine twice, but you ignored it, just demanding all over again that we provide an explanation. See my answer above this comment. Edited May 22, 2021 by John2020
exchemist Posted May 22, 2021 Posted May 22, 2021 7 minutes ago, John2020 said: When motion is involved, pictures are useless. It requires videos instead. I am asking you how you explain and not how I see it. However, you still ignore Newton's 3rd law for an isolated system. Do whatever you like, I don't care. Contact forces are supporting and not excitation forces. You are forcing me to refer to the rotating unbalance for once more. Since you are good at maths (and not only you), if you check the second order inhomogeneous differential equation and its particular solution, you will realize as the differential equation as also its solution, may justify only the response of the system. In terms of physics, it fails to justify the cause of the effect of vibration of the isolated system itself (no external excitation forces, no gravity, nothing) since there are only internal forces at play. If you do not agree with the above statement then, you cannot clearly identify all parts of the differential equation. I just found quickly an image from internet showing the differential equation. See below: Could you show me the excitation force on the above differential equation? Isn't just the RHS of the equation or not? Now in order to simplify the above system, remove the stiffness (k) and the damping coefficient (c). What remains? Note: Gravity is not taking into account (see differential equation) therefore the system is isolated. It means the system vibrates in absence of external forces. This differential equation is irrelevant. In your ferrite ring, the vibration is excited by the AC current: either by the stretching of the coil I referred to or the magnetostriction effect or both. The vibration causes the contact force from the table to vary, since the surface of the ferrite in contact with the table is moving up and down. This accelerates the centre of gravity of the ferrite, first in one direction and then in the other. It is just like you jumping up and down on the spot.
John2020 Posted May 22, 2021 Author Posted May 22, 2021 1 minute ago, exchemist said: This differential equation is irrelevant. I shared the above as a reply to swansont regarding that internal forces are the cause of vibration (we speak always for the experiments and the similarity with a rotating unbalance) where the differential equation cannot justify (I think this is very clear, although you tend to ignore it). Your blender vibrates because it is a rotating unbalance and not a vibrating string with a mass attached. In absence of gravity, it would have the same behavior (vibrating). 8 minutes ago, exchemist said: The vibration causes the contact force from the table to vary, since the surface of the ferrite in contact with the table is moving up and down. This accelerates the centre of gravity of the ferrite, first in one direction and then in the other. It is just like you jumping up and down on the spot. You still have the focus on Exp #1, which is more complicated I would say. Please revisit the About me section of my Profile and watch the LEGO car (Exp #2) and the rotating ring (Exp #3) videos. Those two experiments have nothing to do with your claims above. Especially, the rotating ring (Exp #3) where the rotation is controlled by manually shifting the excitation frequency (increasing frequency -> clockwise rotation, decreasing frequency -> counterclockwise).
swansont Posted May 22, 2021 Posted May 22, 2021 1 hour ago, John2020 said: However, you still ignore Newton's 3rd law for an isolated system. I’m ignoring it because it’s not isolated. The ring is sitting on the table. Quote Contact forces are supporting and not excitation forces. This is nonsense. I can’t be sure how much you’re just making up; “excitation force” is not a term I’ve ever heard in a mechanics problem, and also, this is clearly false/misapplied. There are a number of ways a normal force can cause motion. In this case, the table will vibrate in response, and likely have different modes excited than what’s in the ring. Quote You are forcing me to refer to the rotating unbalance for once more. You got that wrong, so I doubt this will help. Quote since there are only internal forces at play. No matter how many times you repeat this, it will not be true. The vibrating table is external. How you can ignore this is truly mind-boggling. Quote Could you show me the excitation force on the above differential equation? “Excitation force” isn’t a thing (in my experience), so no. I can’t show the Narnia force, either. But the force the table exerts would be modeled as the spring, and it would not have k=0. You’ve simplified the example to the point where it’s flat-out wrong. 50 minutes ago, exchemist said: It is just like you jumping up and down on the spot. According to John2020’s analysis, you can’t jump up and down on a trampoline. Nobody knows how they work.
John2020 Posted May 22, 2021 Author Posted May 22, 2021 (edited) 14 minutes ago, swansont said: This is nonsense. I can’t be sure how much you’re just making up; “excitation force” is not a term I’ve ever heard in a mechanics problem, and also, this is clearly false/misapplied. There are a number of ways a normal force can cause motion. In this case, the table will vibrate in response, and likely have different modes excited than what’s in the ring. 14 minutes ago, swansont said: No matter how many times you repeat this, it will not be true. The vibrating table is external. How you can ignore this is truly mind-boggling. What force is responsible for the vibration of the table (whîch is actually an external component)? The system vibrates and since it is in contact with the table, it will inevitably transmit the vibration to the table, too. Consequently, the force comes from inside the system, the ring itself. 14 minutes ago, swansont said: “Excitation force” isn’t a thing (in my experience), so no. I can’t show the Narnia force, either. But the force the table exerts would be modeled as the spring, and it would not have k=0. You’ve simplified the example to the point where it’s flat-out wrong. By setting the stiffness and the damping coefficient to zero the system will still vibrate since the force comes from inside the ring. When you take e.g. the rotor with the eccentric mass in outer space (in void) in absence of gravitational forces, the rotating unbalance will still vibrate. Excitation is the force being the cause of vibration (it is actually the initial cause). In the example with the rotating unbalance the role of the excitation is being played by the centripetal force (see Rotor Excitation graph above). When the eccentric mass does not rotate then there is no excitation force, resulting in no vibration of the system. Edited May 22, 2021 by John2020
swansont Posted May 22, 2021 Posted May 22, 2021 7 minutes ago, John2020 said: What force is responsible for the vibration of the table (whîch is actually an external component)? The system vibrates and since it is in contact with the table, it will inevitably transmit the vibration to the table, too. Consequently, the force comes from inside the system, the ring itself. The ring’s vibrations cause the table to vibrate. This is an action-reaction force from Newton’s 3rd law. The table is, as you note, an external component. So: force exerted by the table causes the ring to accelerate (in accordance with Newton’s 1st and 2nd laws) 17 minutes ago, John2020 said: By setting the stiffness and the damping coefficient to zero the system will still vibrate No, when you set k to zero you will not have oscillations.
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