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Quote from: Bored chemist on 16/10/2020 17:58:20Quote 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.Hence what I am trying to get across. The devil is in the detail.
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.
If the bearings are friction-less then CDs are not part of the system in this exact scenario.
Escaping to unrealistic assumptions, really?
Quote from: Kryptid on 16/10/2020 17:55:37Quote 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?Just think about this exact scenario and tell us how you can change the rotation of the CDs inside?
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?
Quote from: Jaaanosik on 16/10/2020 17:53:15If we change time boundaries during the CDs acceleration then we need to specify ideal EM field (no skipping), again some unrealistic stuff.It may be a language thing,but that makes no sense.No EM field is involved.Time isn't good at obeying boundaries.What do you mean?
If we change time boundaries during the CDs acceleration then we need to specify ideal EM field (no skipping), again some unrealistic stuff.
Quote from: Bored chemist on 16/10/2020 18:12:31Quote from: Jaaanosik on 16/10/2020 17:53:15If we change time boundaries during the CDs acceleration then we need to specify ideal EM field (no skipping), again some unrealistic stuff.It may be a language thing,but that makes no sense.No EM field is involved.Time isn't good at obeying boundaries.What do you mean?What happens when the external momentum would be applied at the time when the CD players are turned on and the CDs are accelerating.
Rather Than us defining the system and you wriggling out of it, perhaps we could look at it the other way round.Please show us what impulse you could apply to the two pairs of players which would give rise to them following different motions
Quote from: Jaaanosik on 16/10/2020 18:18:21Quote from: Bored chemist on 16/10/2020 18:12:31Quote from: Jaaanosik on 16/10/2020 17:53:15If we change time boundaries during the CDs acceleration then we need to specify ideal EM field (no skipping), again some unrealistic stuff.It may be a language thing,but that makes no sense.No EM field is involved.Time isn't good at obeying boundaries.What do you mean?What happens when the external momentum would be applied at the time when the CD players are turned on and the CDs are accelerating.Exactly the same as when they were stationary, or at full speed.At all time the total angular momentum is zero.
By symmetry, whatever you added to one disk, you subtracted from the other, and so the effects cancel.
Quote from: Bored chemist on 16/10/2020 18:45:57By symmetry, whatever you added to one disk, you subtracted from the other, and so the effects cancel.No, that's my point about the random friction. There is no symmetry.
Two things.First, there's no friction in the system under discussion,Second, random stuff cancels out on average.
Quote from: Jaaanosik on 16/10/2020 20:31:57Quote from: Bored chemist on 16/10/2020 18:45:57By symmetry, whatever you added to one disk, you subtracted from the other, and so the effects cancel.No, that's my point about the random friction. There is no symmetry.Two things.First, there's no friction in the system under discussion,Second, random stuff cancels out on average.
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.Nonsense. This violates momentum conservation laws. I can build a reactionless spaceship drive if this ludicrous statement is true.
How do we spin the CDs that are on the friction-less bearings?
Any friction in a CD player is countered by a motor keeping the CD rotating at a constant relative speed, required for the music to play properly.
To be fair, I wrote that out of the discussion by saying we were considering a model where friction must be so small you can ignore it.
The external momentum as per the image.
He's adding needless complication in effort to never have to actually make such a statement.
Jano of course has no clue what he's talking about and has not explicitly spelled out a single scenario with an explicit statement about the difference in behavior between a pair of zero-momentum devices running or not.
That said, strap two CD players face to face an despite the two motors doing work, you cannot tell if the things are running or not. The internal torque by the two motors always cancel each other and there is no external effect.
Let's go slowly.
Two CD players taped together, CDs inside, not spinning, friction-less bearings.The external momentum as per the image.
What happens?The CD players rotate, the CDs inside do not rotate.
Any translation?