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Quote from: Jaaanosik on 16/10/2020 15:47:20When the CD players are ON then we need to consider the 'elasticity' of EM field of the motors.One CD will be accelerated and the other will be decelerated when we apply the same external momentum as per the image.Once the disks are spinning then the motors have no work to do (apart from overcoming bearing losses which, in principle could be practically zero).So you can switch the motors off at that stage.There's no EM field needed.So there's no need to consider any elasticity it might have.Quote from: Jaaanosik on 16/10/2020 15:52:47My post above shows what you missed.NoIt shows that you do not understand physics.
When the CD players are ON then we need to consider the 'elasticity' of EM field of the motors.One CD will be accelerated and the other will be decelerated when we apply the same external momentum as per the image.
My post above shows what you missed.
Quote from: Jaaanosik on 16/10/2020 15:47:20We apply the external forces as per the image, in the CDs parallel plane.Quote from: Jaaanosik on 16/10/2020 15:47:20This is what I meant when I said: "The external momentum will distribute through the system differently and therefore the systems will move (translate/rotate) differently."Why did you talk about that?The question was about what happens after the disks are spinning.There's a difference between the case of having the disks locked in place or not.But since we are talking about CD players, and since I talked about being able topers play on the remote control, and get the disks spinning, it is clear that we are talking about the case where the discs can rotate.Why are you talking about some nonsensical system where the discs won't play?
We apply the external forces as per the image, in the CDs parallel plane.
This is what I meant when I said: "The external momentum will distribute through the system differently and therefore the systems will move (translate/rotate) differently."
Escaping to unrealistic assumptions, really?
It is you that does not understand the real world physics.
OKSo, let's try to agree a simple system that actually addresses the point.There is no air resistance.The bearings are frictionless and the motors are ideal so that, once they are up to speed the back emf exactly balances the applied voltage, no current flows and they draw no power. As a consequence, they produce no torque once the disks are spinning at 5 revs per second. The disks "coast" after that.The two players are identical.They are taped rigidly together feet to feet so that the angular momentum of the disks (and motors, for what it's worth) are identical in magnitude, but opposite in direction.The cd players are (nearly) perfectly rigid (A perfectly rigid material would breach relativity).We are doing the experiment in microgravity, so the effect of gravity from surrounding objects is small enough to ignore.The players have remote controls which use IR or some such and which lets you start or stop them remotely without applying a significant force to them (we can ignore photon pressure from the IR).The "stop" button on the remote actually drives the motor in reverse to apply a breaking force until the disk stops WRT the player and then switches off the drive power.No other significant forces act on the players except those explicitly stated as part of the experiment.Anything else we need to clarify?
Quote from: Jaaanosik on 16/10/2020 16:24:40It is you that does not understand the real world physics.Said the guy who thinks conservation of angular momentum can be violated.
Not really, it is all about the space and time boundaries of the system discussed.
Quote from: Jaaanosik on 16/10/2020 17:33:21Not really, it is all about the space and time boundaries of the system discussed.I have seen you argue that linear momentum and angular momentum can be interconverted. That leads to violations of both conservation of linear momentum and angular momentum.
OK, what's next?
Do we have an agreement that the system demonstrates different attributes, the system behaves differently due to the internal motion of inner parts even thought the total net angular momentum is the same before the external impulse?
First thing to recognize is the difference.The 3 CD players at 0:49s when the CDs are not spinning inside.There is an external impulse to the system of connected 3 CD players when they are not running.The system starts to rotate/spin.The system center of mass moves/translates at velocity v1.The CDs are spinning inside at 0:55s.There is an external impulse (it appears to be the same magnitude, but off center) to the system of connected 3 CD players when the are running (CDs are spinning inside).The system does not start to rotate. The system wobbles.The system center of mass does not move/translates at velocity v1 (magnitude).The system center of mass is resisting the straight line motion/translation.
What momentum was applied? Angular or linear?
They can
Quote from: Jaaanosik on 16/10/2020 17:31:04OK, what's next?OK, you presumably remember asking thisQuote from: Jaaanosik on 12/10/2020 15:41:44Do we have an agreement that the system demonstrates different attributes, the system behaves differently due to the internal motion of inner parts even thought the total net angular momentum is the same before the external impulse?And saying thisQuote from: Jaaanosik on 12/10/2020 15:41:44First thing to recognize is the difference.The 3 CD players at 0:49s when the CDs are not spinning inside.There is an external impulse to the system of connected 3 CD players when they are not running.The system starts to rotate/spin.The system center of mass moves/translates at velocity v1.The CDs are spinning inside at 0:55s.There is an external impulse (it appears to be the same magnitude, but off center) to the system of connected 3 CD players when the are running (CDs are spinning inside).The system does not start to rotate. The system wobbles.The system center of mass does not move/translates at velocity v1 (magnitude).The system center of mass is resisting the straight line motion/translation.Now, imagine wto pairs (as discussed) of CD players.One has the two disks spinning and the other does not.You apply a similar impulse to the two pairsAs you put it "There is an external impulse (it appears to be the same magnitude, but off center)"But let's' be clear; in this case it is exactly similar, the same push in the same place on the shell of the CD player.Do you believe that the motion of the two systems would be different. To sum up, the only difference is that the disks are (contra) rotating in one, but stationary in the other.
If the bearings are friction-less then CDs are not part of the system in this exact scenario.
Quote from: Jaaanosik on 16/10/2020 17:42:28They canAnd thus you prove my original point.
Quote from: Jaaanosik on 16/10/2020 17:53:15If the bearings are friction-less then CDs are not part of the system in this exact scenario.That may be true in the case where the impulse is exactly tangential to the rotation axis, but it is not true in general.
Did the momentum of the CD player system changed when the external momentum was applied?Where is the conservation? What boundaries are we talking about?
Quote from: Jaaanosik on 16/10/2020 17:53:15If the bearings are friction-less then CDs are not part of the system in this exact scenario.Seriously? Since when did friction define whether or not something was a part of a system or not?
If we change time boundaries during the CDs acceleration then we need to specify ideal EM field (no skipping), again some unrealistic stuff.