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Stonehenge
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Registered: 06/20/04
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Re: Distance and Time [Re: DieCommie]
#15022298 - 09/03/11 11:30 AM (12 years, 8 months ago) |
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>rocket is never in an inertial frame
The rocket is moving relative to the earth. The earth is moving relative to the rocket. You can't say the earth is standing still and only the rocket is moving. It matters not which is the more massive object. The earth is moving in relation to the sun. The earth is moving much faster than that in relation to the galactic core. All speed is relative. I don't blame you for not being able to solve the question. It's a very hard one.
There are galaxies moving away from us at a high percentage of the speed of light. Someone who is at rest in relation to that galaxy will be zooming by the earth. To the people on that rocket, the earth is the one moving fast. Who is correct? It's all relative.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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DieCommie

Registered: 12/11/03
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Quote:
All speed is relative. I don't blame you for not being able to solve the question.
Save your condescending remarks. I understand the problem fully and already provided you a complete explanation. Re-read my posts and think it through. Do you know what an inertial frame is?
BTW, its not really that hard of a problem. This was the very first subject we did in my very first physics class as an undergraduate. Its an advanced freshmen level problem.
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Stonehenge
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Re: Distance and Time [Re: DieCommie]
#15023857 - 09/03/11 05:16 PM (12 years, 8 months ago) |
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Then oh great one can you explain to us mere mortals why an inertial frame makes the speed between objects irrelevant? Instead of saying read the links or you already explained it, explain in detail if you do indeed understand. If you have no idea then continue on.
Einstein said that all speed was relative. The time dilation concept derives from high relative velocities which are stipulated in the example i gave.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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DieCommie

Registered: 12/11/03
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Edited by DieCommie (11/11/16 09:50 AM)
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johnm214


Registered: 05/31/07
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Loc: Americas
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Stonehenge, please cut out the condescending remarks and sarcastic personal commentary. Discuss the issue, not the person.
I've noticed this is somewhat common in your posts here, but it needs to stop. You can discuss germane ideas without limitation, howerver; this is not true in the case of irrelevant personal appeals.
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Stonehenge
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Re: Distance and Time [Re: johnm214]
#15027565 - 09/04/11 12:35 PM (12 years, 8 months ago) |
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John, i said it was a hard question and it is. That is not being condescending, it's the truth. If dc decides he is offended by being told his answer is wrong that does not make what i said an insult.
DC you still have not explained anything.
>Consider an astronaut and a space craft, and consider conservation of energy. The astronaut is in an inertial frame so he can claim that he is still and his ship is moving.
His ship is moving relative to the earth or some other frame of reference. He can claim he is still in relation to the ship but he is moving in relation to the earth or whatever point of reference you want to make.
>He observes his ship has kinetic energy of one half m v squared. He fires his rocket and 'boosts' into a different inertial frame.
I assume you mean accelerates the ship since you have used the terms rocket and ship.
>He changes his velocity, is momentarily in a non-inertial frame, and then comes to a rest relative to the ship. He is now again in an inertial frame and can claim he is at rest.
At rest relative to the ship, not to where he started from or any other point.
>He now calculates that the ship has zero kinetic energy - and he is right! He calculates that the exhaust from his boosting rockets has nowhere near enough energy to make up for the difference. He concludes that conservation of energy does not hold.
This contains many errors. Zero kinetic energy in relation to what? All speed is relative as you agreed before. Kinetic energy has to have a point of reference. We are at rest in relation to the earth but we are spinning around the sun and the earth itself is spinning. So we are experiencing motion even if we don't feel it. The conclusions drawn by your astronaut are incorrect.
>What is wrong with his thinking? He is comparing the situation in one inertial frame to that in another inertial frame. That is not how conservation laws work. You have to compare apples to apples, you have to compare conserved quantities from within the same inertial frame.
You can compare conservation of energy in regard to any frame of reference. It will work and has to work in all those reference points. For example, if he is moving at speed toward the moon, he has kinetic energy in regard to the moon and if he hits it, that energy will cause the ship to be smashed. He will have a different kinetic energy in regard to the earth, to the sun, to other planets or to a piece of debris floating by. By firing the rocket he changes the kinetic energy he has in regard to each of those systems. He might be moving slower in regard to the moon, faster toward the earth and at an angle to another point
>This is where you are going wrong as well. In your first situation you can use an inertial frame of the earth. And you can also use an inertial frame of your space ship until it 'boosts' by changing inertial frames. At that point you have to consider your inertial frame to be still moving away from the earth, not towards it like the space ship.
Sorry, that makes no sense. I was speaking of a rocket passing by the earth at speed. It has velocity relative to the earth. The earth has velocity relative to the ship.
>In your second situation you made the resolution even clearer. You made it such that the space ship is never in an inertial frame, it is constantly accelerating. In that case, you can still use the inertial frame of the earth. But for the space ship, you can only choose a frame that it occupies for an instant. You can choose one that is the same as the ships when it begins, or when it is half way around. But your ship will constantly be accelerating (or 'boosting') out of your inertial frame. In that case, you can still use the inertial frame of the earth. But for the space ship, you can only choose a frame that it occupies for an instant. You can choose one that is the same as the ships when it begins, or when it is half way around. But your ship will constantly be accelerating (or 'boosting') out of your inertial frame.
The ship will have an acceleration due to traveling in a circular path. It still has a velocity in relation to the earth. At some point it's going away, at some point it's going at right angles, at some point in the circular path it is heading toward the earth. The point being that it is always moving at speed in relation to the earth. I will grant you that the speed varies but that makes no difference. We can take the average speed and i said it had a time dilation of one day per month which corresponds to an average speed which is fairly fast.
>To resolve the apparent paradox, pick an inertial frame and don't change it half way through your situation - stay with it. Then calculate your time dilation and see that there is never really a paradox at all. I can help you with this if you want. If you read the original paper on relativity its clearly explained in there too. (As well as any general university physics textbook )
Now who is being condescending? Your mistake as i see it is that you seem to think that if the ship is changing velocity then the rules fly out the window. We have not changed the frame of reference. It always has a high speed in relation to the earth. A changing speed in relation to a fixed point, in this case the earth, just means the time dilation will change over the course of the orbit but you can still calculate an average.
Lets go back to the first example since the second seems confusing. The ship is moving fast in relation to the earth. The earth is moving fast in relation to the ship. Which one experiences time dilation and why?
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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DieCommie

Registered: 12/11/03
Posts: 29,258
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Quote:
Your mistake as i see it is that you seem to think that if the ship is changing velocity then the rules fly out the window.
Nope, you are seeing it wrong. Your mistake is that you think you can use a ship with a changing velocity as a reference frame. You cannot. That is the rule you are throwing out the window.
Quote:
Lets go back to the first example since the second seems confusing. The ship is moving fast in relation to the earth. The earth is moving fast in relation to the ship. Which one experiences time dilation and why?
From what inertial frame? Dont forget, what I said... "To resolve the apparent paradox, pick an inertial frame and don't change it half way through your situation - stay with it. Then calculate your time dilation and see that there is never really a paradox at all. I can help you with this if you want."
So pick an inertial frame, and then you can ask how much each one ages relative to that inertial frame. Change your inertial frame half way through, and you will get nonsensical nonphysical results.
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Stonehenge
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Re: Distance and Time [Re: DieCommie]
#15029027 - 09/04/11 05:07 PM (12 years, 8 months ago) |
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>Your mistake is that you think you can use a ship with a changing velocity as a reference frame. You cannot. That is the rule you are throwing out the window.
OK, so you are saying that we must stick to one inertial frame of reference and ignore everything else ? And why is that? The universe is not that simple. A star in a far away galaxy does exert an influence on life here although very slight. All things are interconnected and you can't just look at things in a vacuum while ignoring everything else. Show me where this law is you are quoting? And not a link to a long website. There is nothing in newton's laws of physics that says this nor did einstein, that i'm aware of say that.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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DieCommie

Registered: 12/11/03
Posts: 29,258
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Edited by DieCommie (11/16/16 10:09 AM)
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Stonehenge
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Re: Distance and Time [Re: DieCommie]
#15032697 - 09/05/11 01:08 PM (12 years, 8 months ago) |
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No, i don't think that is it. OK, now i have to admit i'm not sure i have the answer myself. I will present a theory or two though i've already found one or two possible holes in the logic.
If the observer on earth sees the rocket flying past at a high rate of speed, it will seem to be undergoing time dilation and be behind the rate of time on earth. The observer in the rocket sees the earth flying by at a high rate of speed and sees the earth undergoing time dilation while his time is normal. The reason for this is because the man in the craft is not moving at speed in regards to the rocket but the rocket, the calendar and the rocket's observer are moving from the point of view of the earth.
So the time dilation the earth sees in the rocket is correct and the time dilation seen by the rocket is true for that observer. Which one is moving fast depends on your point of view and the time dilation also depends on the point of view. Both observers are correct using their frame of reference.
Can anyone add to this or find some major flaw? Or come up with a better theory? DC i'm sure this is what you were trying to say, right?
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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DieCommie

Registered: 12/11/03
Posts: 29,258
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I suspect Im the most patient poster around here when it comes to explaining science. Most of our local experts wouldnt even bother. I think you understand it better now though.
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Stonehenge
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Re: Distance and Time [Re: DieCommie]
#15042925 - 09/07/11 01:48 PM (12 years, 8 months ago) |
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It's not a matter of patience, its a matter of not being familiar with the material. Like i said, it was not an easy question but i think my answer comes close and is valid by itself. I was hoping someone would offer more insights but it's a rare bird who knows about this stuff outside of something they can quote out of a book.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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