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Quote from: Jaaanosik on 22/04/2020 06:53:53Dictionary is not a textbookYour point being what?Quote from: Jaaanosik on 22/04/2020 06:45:06There is no answer till we settle the closed system definition.The spaceship is an isolated system. That is clearly defined. No matter or energy is entering or leaving the system. No momentum is entering or leaving the system either.So if a system does not have momentum entering or leaving it, you understand that the momentum must remain unchanged, yes?
Dictionary is not a textbook
There is no answer till we settle the closed system definition.
Do you understand what it means?
The cat is isolated system, correct?
How the cat could start the rotation without an external impulse?
Quote from: Jaaanosik on 22/04/2020 07:03:41Do you understand what it means?Yes, it means that executing a rotation does not require net momentum (unlike your engine, which does require net momentum).Quote from: Jaaanosik on 22/04/2020 07:03:41The cat is isolated system, correct?For the sake of discussion, yes.Quote from: Jaaanosik on 22/04/2020 07:03:41How the cat could start the rotation without an external impulse?Because net momentum isn't needed for a rotation (but net momentum is needed for your spaceship to go forward). I've already said that before.The thing about the gyroscope is ultimately irrelevant. Even if I was utterly unable to explain anything about gyroscopes, I can still point to Noether's theorem as proof that you can't interconvert angular and linear momentum.
I'll just say an isolated system is not a closed system
The isolated system can generate momentum
You are mistaken about the wobble.Check how big wobble is for the CD players.
What is this torque?
How is this torque used on ISS?
Quote from: Jaaanosik on 22/04/2020 07:21:40I'll just say an isolated system is not a closed systemAccording to the definitions that you have provided in your Wikipedia link, an isolated system is even more cut off from the outside world than a closed system is. A closed system allows for the transfer of energy but not matter, whereas an isolated system does not allow for the transfer ot either energy or matter.Quote from: Jaaanosik on 22/04/2020 07:21:40The isolated system can generate momentumHow is it going to generate momentum when (1) it can't receive momentum from an outside source, and (2) momentum is conserved?
Quote from: Jaaanosik on 22/04/2020 07:21:40You are mistaken about the wobble.Check how big wobble is for the CD players.Even if I am, so what? It won't help your engine work.Quote from: Jaaanosik on 22/04/2020 07:21:40What is this torque?https://en.wikipedia.org/wiki/TorqueQuote from: Jaaanosik on 22/04/2020 07:21:40 How is this torque used on ISS?I presume it is used to reorient the ISS and make it stable against changes in orientation. But that doesn't change the net angular momentum of the ISS nor does it help your engine work.You have agreed with me that your ship starts with zero angular momentum and zero linear momentum. You have agreed that conservation of momentum is true. The ship is an isolated system. Putting these three things together, the ship cannot ever have a net momentum that isn't zero. There is no angular momentum present, so you can't argue that it can be changed into linear momentum because zero can't become a positive number. No momentum is entering the ship from an outside source nor is momentum leaving the ship to an outside source. So tell me already: how can zero net momentum in an isolated system turn into positive net momentum without violating conservation of momentum?
Are we sure the cat generated no net angular momentum?
The orientation of the body seems to be different.
We stop the CMG rotations before they hit the spaceship back.
What would be the result? A forward net momentum
Quote from: Jaaanosik on 22/04/2020 18:53:14Are we sure the cat generated no net angular momentum?Yes, because Noether's theorem says so. Do you even know what a conservation law is?Quote from: Jaaanosik on 22/04/2020 18:53:14The orientation of the body seems to be different.Of course it's different. Changing orientation doesn't require net momentum.Quote from: Jaaanosik on 22/04/2020 18:53:14We stop the CMG rotations before they hit the spaceship back.What force is stopping the CMG?Quote from: Jaaanosik on 22/04/2020 18:53:14What would be the result? A forward net momentumI don't really need to explain to you why zero angular momentum plus zero linear momentum equals positive linear momentum is bad math, do I?As long as you keep arguing that 0 + 0 = positive number I am going to stand against it because it is wrong.
Anything to say?
Quote from: Jaaanosik on 22/04/2020 23:26:59Anything to say?No. The Cubli doesn't violate conservation of angular momentum (nothing ever does), so there is nothing to say.
Is Cubli a closed system?
If yes then it needs an external force to change the momentum.
Do you see any external force that causes the jump up?
Quote from: Jaaanosik on 23/04/2020 01:09:54Is Cubli a closed system?Depends on which definition of "closed system" you are going for.
Quote from: Jaaanosik on 23/04/2020 01:09:54If yes then it needs an external force to change the momentum.The momentum doesn't change...Quote from: Jaaanosik on 23/04/2020 01:09:54Do you see any external force that causes the jump up?No, because no such force is needed. I already told you once that changing orientation does not require a change in net angular momentum.Momentum is conserved. Period. If you think you've found a case where it isn't, it's only because your analysis of it was either flawed or incomplete. We know that beforehand even without having to get into the details of how the system works. Noether's theorem guarantees it.
The textbook definition for now.
Cubli is not a closed system. Agreed?
CMGs are not a closed system.
There is no point in talking that a momentum is conserved if the system is not closed.
Quote from: Jaaanosik on 23/04/2020 03:18:54The textbook definition for now.The one that says a closed system doesn't allow matter to be transferred but energy can?Quote from: Jaaanosik on 23/04/2020 03:18:54Cubli is not a closed system. Agreed?If it was an open system, then matter would be transferred in and out of it. What matter is being transferred in and out of the Cubli?
Thus, if there is no angular impulse about a fixed point (or about the mass center), the angular momentum of the system about the fixed point (or about the mass center) remains unchanged.
Quote from: Jaaanosik on 23/04/2020 03:18:54CMGs are not a closed system.Of course not. They are interacting with the other components of the ship. But the other components of the ship don't have any momentum that they can give to the CMGs. The CMGs don't have any momentum to give to the other components of the ship either (remember, you agreed that the system has zero momentum before the engine is cut on).
...Quote from: Jaaanosik on 23/04/2020 03:18:54There is no point in talking that a momentum is conserved if the system is not closed.You know why that is, don't you? It's because an open system can change its momentum by interacting with outside systems. Your ship is not interacting with other systems because it is an isolated system. No mechanism exists by which it can receive momentum from somewhere else. And if you did rely on receiving momentum from an outside source, then that would pretty much mean that you have abandoned your claim that you can give the ship net momentum just by manipulating its internal components.To drive this home, consider a universe that is completely empty of all energy and matter with the exception of your spaceship and an astronaut that is floating right behind it. The spaceship is turned off and the astronaut sees the ship as stationary in their reference frame. Since the astronaut obviously sees themself as being stationary as well, then they know that the total momentum in their universe is zero (the ship's momentum plus the astronaut's momentum equals zero).Now you turn the engine on. According to you, the ship will begin to move forward and leave the astronaut behind. The astronaut goes about measuring the total momentum of the universe a second time. This time, the moving ship does have momentum from the astronaut's reference frame. They take the measurements, do the calculations and find that the ship's momentum plus the astronaut's momentum is now a positive number. This means that a closed system (the entire universe) has experienced an increase in net momentum.We know, of course, that such a thing is impossible because momentum is a conserved quantity. A closed system cannot go from zero momentum to positive momentum. This is how we know that the scenario I just described cannot happen in the real world. It isn't possible for the ship to move because it will increase the total momentum of a closed system.
This is a completely worthless discussion. You are just as bad at physics as Dave Lev is. You don't understand what conservation laws are. You don't understand what a closed system is. And nothing I can do will be able to alleviate that ignorance. So I'm ending my attempt to educate you.You might as well be arguing that you can charge up a dead battery using another dead battery, because if you believe that momentum can be created, then you might as well believe that energy can be created too. Conservation laws have no meaning to you.
you left out the engine gas.