Z.10.46 Posted August 21 Share Posted August 21 Hi, A superfluid has zero viscosity. If a vortex is created, it can rotate indefinitely without any loss of energy. There are objects less dense than a superfluid that can float on its surface, where a magnet can be placed. If a vortex is created in this liquid, the magnet will move indefinitely. If a bulb is placed in a closed circuit next to a moving magnet, the bulb will light up through electromagnetic induction. Here, the purpose of these questions is to understand why the bulb does not always light up through electromagnetic induction, even if the magnet moves indefinitely due to the vortex properties of a superfluid... What is the behavior of a magnet floating in a superfluid that rotates indefinitely? Why doesn’t the bulb light up indefinitely, even if the magnet moves indefinitely without any loss of energy? Link to comment Share on other sites More sharing options...
MigL Posted August 21 Share Posted August 21 A superfluid will rotate almost indefinitely due to almost zero frictional losses, and viscosity. The floating platform supporting the magnet will not be dragged along because it has inertia and no friction to drag it. ( the fluid is essentially a 'frictionless' surface ) If it did, the fluid would need to do work to overcome the inertia, and the energy to do that work would need to come from somewhere as we have well established conservation laws. You cannot make a perpetual 'lighting' machine. Link to comment Share on other sites More sharing options...
exchemist Posted August 21 Share Posted August 21 5 hours ago, Z.10.46 said: Hi, A superfluid has zero viscosity. If a vortex is created, it can rotate indefinitely without any loss of energy. There are objects less dense than a superfluid that can float on its surface, where a magnet can be placed. If a vortex is created in this liquid, the magnet will move indefinitely. If a bulb is placed in a closed circuit next to a moving magnet, the bulb will light up through electromagnetic induction. Here, the purpose of these questions is to understand why the bulb does not always light up through electromagnetic induction, even if the magnet moves indefinitely due to the vortex properties of a superfluid... What is the behavior of a magnet floating in a superfluid that rotates indefinitely? Why doesn’t the bulb light up indefinitely, even if the magnet moves indefinitely without any loss of energy? Because the induction will act as a brake on the rotating magnet. Just like regenerative braking on a locomotive or an electric vehicle. The bulb radiates electromagnetic energy, which comes from the kinetic energy of rotation of the magnet. So it will slow down and stop. Link to comment Share on other sites More sharing options...
Z.10.46 Posted August 21 Author Share Posted August 21 (edited) The rotation of the magnet comes from the endless rotation of the superfluid. Does slowing down the magnet affect the rotation of the superfluid even if there is no friction? So in the end the vortex will stop. Have we already done this experiment? Clearly I don't understand, will the magnet stop rotating even if the vortex rotates, or is it the vortex that will stop? Edited August 21 by Z.10.46 Link to comment Share on other sites More sharing options...
exchemist Posted August 21 Share Posted August 21 39 minutes ago, Z.10.46 said: The rotation of the magnet comes from the endless rotation of the superfluid. Does slowing down the magnet affect the rotation of the superfluid even if there is no friction? So in the end the vortex will stop. Have we already done this experiment? Clearly I don't understand, will the magnet stop rotating even if the vortex rotates, or is it the vortex that will stop? The induction is due to the magnet, right? So the magnet will lose energy. If the fluid is frictionless, the vortex can continue, since the slowing down of the magnet will not slow down the rotation of the fluid. Link to comment Share on other sites More sharing options...
Z.10.46 Posted August 21 Author Share Posted August 21 electromagnetic induction comes from the movement of a magnet, and the movement of the magnet comes from the movement of the superfluid. I don't understand why the magnet will freeze in place even if it's moving by the vortex? In any case, I believe that the outcome of this experience is that the vortex will stop but I am not sure... Link to comment Share on other sites More sharing options...
MigL Posted August 21 Share Posted August 21 A superfluid is characterized by no ( or very close ) viscosity; look it up on Wiki. Once set in motion or spinning, it will do so indefinitely as it has no internal friction. It will 'climb' up the sides of open containers, against gravity, and escape, coating inside and outside walls. It will not demonstrate shearing stresses between differing flows, or boundary surfaces ( no boundary layer ). It will, in effect, present a frictionless surface to whatever is floating the magnet; so what is compelling the magnet to move ??? And if there is no motion, there is no induction to consider. Physics 101: Will a rotating tire on a frictionless surface move the car ??? Link to comment Share on other sites More sharing options...
KJW Posted August 22 Share Posted August 22 It should be remarked that a rotating superfluid behaves differently to other rotating fluids, exhibiting quantized vortices. Link to comment Share on other sites More sharing options...
Z.10.46 Posted August 27 Author Share Posted August 27 Yes, the superfluid vortex is a quantum phenomenon. It is often assumed that the cause is the absence of viscosity, but if the cause is actually a quantum energy, then the light bulb would continue to glow indefinitely. In any case, with this experiment, we can truly determine whether the reason the vortex keeps spinning is due to the lack of viscosity or some other unknown energy. Link to comment Share on other sites More sharing options...
MigL Posted August 27 Share Posted August 27 ALL effects, including lack of viscosity, are quantum effects. Link to comment Share on other sites More sharing options...
sethoflagos Posted August 27 Share Posted August 27 7 hours ago, Z.10.46 said: Yes, the superfluid vortex is a quantum phenomenon. We're not there yet. Your OP seemed to suggest an inviscid classical orbital velocity field about some (undefined) axis of rotation: ie some particular solution of the Euler equations for some undefined geometry. The first thing you have to help us get our heads around is what exactly you mean by the word 'vortex' for a system that sounds as if it should have a local vorticity field value of zero throughout. It will differ appreciable from the familiar(ish) picture we have of vortex phenomena in viscous fluids. Maybe tell us the geometry of your containment? How you get the superfluid rotating in the first place? How does local fluid velocity vary with distance from the axis of rotation? Reassure us that the Euler equations aren't going to start producing singularities (which they are apt to do when presented with non-physical boundary conditions) On 8/21/2024 at 2:04 AM, MigL said: You cannot make a perpetual 'lighting' machine. Probably easier just to start and finish with this. On 8/21/2024 at 4:44 PM, MigL said: Physics 101: Will a rotating tire on a frictionless surface move the car ??? Will a frictionless wall stop the car? 🤔 (I don't think this is quite as silly a question in context as it sounds. Again, how would one persuade a superfluid to rotate?) Link to comment Share on other sites More sharing options...
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