about Bob's article on absolute or relative time

Stripe

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My mistake for not being clearer. When I said the “only change is the mass of body 2” I was referring to the only change needed from the values I had just itemized (body 1 mass of 100, zeros for body 1 speeds and positions, etc.

That's what I did. If you want to make any more comparisons you're going to have to do them yourself.
 

ThePhy

New member
That's what I did.
No you didn’t. The values shown in the figure you attached are the default values, with the exception of the body 2 mass.
If you want to make any more comparisons you're going to have to do them yourself.
I don’t blame you for deciding to pull the eject handle. Better than slowly burning in the flaming cockpit.
 

Stripe

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No you didn’t.

Yes, I did.

The values shown in the figure you attached are the default values, with the exception of the body 2 mass.

I didn't bother trying to include both sets of values. I just overlaid the second orbit. Those could be the numbers for either. You could always go and enter the numbers yourself. Takes all of a minute. :plain:

I don’t blame you for deciding to pull the eject handle. Better than slowly burning in the flaming cockpit.

I'm not going anywhere. I still think I'm right and you haven't shown me any reason why I should think otherwise. You've got a little maths equation that you're supposedly using, but I'm still quite convinced that it is inappropriate. The simulation I linked to still backs me up. There are numerous other simulators out there that you might link to to show how mine is incorrect ...

In short you've a lot of :blabla: but not a lot of actual explanation.

I'll give you this - my response from common sense is not going to be enough to convince anyone else and this discussion has led me to consider things that I would never have thought of otherwise. :up:
 

GuySmiley

New member
I don't agree. I can't argue with the maths because I'm sure you all know it better than I do, but I cannot fathom how the orbit would not be affected.

If you change an object's mass but maintain its velocity you altered the energy distribution in the scenario. Where does that energy come from or go to?
Well we are magically turning an apple into the moon, where does the energy come from? lol. That why I think all this depends on conservation of momentum or not. But in a theoretically perfect case, the mass shouldn't make a difference. When I say that I immediately think that we ignore the gravitational pull of the object (moon or apple) on the earth, which is reasonable for satellites or apples, but not for the moon. Im sure that simulator doesn't ignore any of that, including the perturbing effects I mentioned earlier.
 

ThePhy

New member
I didn't bother trying to include both sets of values. I just overlaid the second orbit. Those could be the numbers for either.
Precisely. If you had gone to grade school, you would understand those numbers shown in your picture are incorrect for BOTH the moon and the apple orbit. Those are just random values that the person who made the tool supplied. He doesn’t even pretend those are correct for the moon.
You could always go and enter the numbers yourself. Takes all of a minute. :plain:
I did. 5 minutes after you showed me the tool long ago. Still waiting for you to do the same.
I still think I'm right and you haven't shown me any reason why I should think otherwise. You've got a little maths equation that you're supposedly using, but I'm still quite convinced that it is inappropriate. The simulation I linked to still backs me up. There are numerous other simulators out there that you might link to to show how mine is incorrect ...
Oh I don’t expect you to admit failure. Your job in these discussions is comic relief. Rather like HAL – the computer in 2001 – you would have a short circuit if forced to be logical.
 

Stripe

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Precisely. If you had gone to grade school, you would understand those numbers shown in your picture are incorrect for BOTH the moon and the apple orbit. Those are just random values that the person who made the tool supplied. He doesn’t even pretend those are correct for the moon.

I see now why you're so eager for me to use your numbers .. :chuckle:

When I say that I immediately think that we ignore the gravitational pull of the object (moon or apple) on the earth, which is reasonable for satellites or apples, but not for the moon. Im sure that simulator doesn't ignore any of that

The orbit will change, but not as dramatically as I might have implied. The graphic I provided demonstrated a change, with Phy's numbers the change is hidden because the difference is so small.

The common center of mass is the difference that changes when the mass of one object changes. In the earth/moon system the common center is inside the earth, changing the moon to an apple will only move that center within the earth. With a more dramatic change in mass (or closer objects) that center might move outside the interior of the earth (this is what my graphic showed). So here's my conclusion. The orbit will change, but perhaps Phy is justified in pointing out that the change will only be rather small.

Does that make sense?
 
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Stripe

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situation 1:
M100----------X----------M100

situation 2:
M100--X------------------M10

situation 3:
M100X--------------------m1


M=Mass (of an orbiting body).
100/10/1=Arbitrary masses of orbiting bodies.
X=Common centre of gravity for two body system.

Here is why the orbit of the moon would change were it replaced with an apple.

Above we have three situations. In situation 1 two bodies of mass 100 (M100) are in orbit. They do not form a system where one orbits the other. Instead they both orbit a common centre of gravity (X). Just imagine each body being on the end of a T-section pole is being rotated at the red X. This rule applies in all cases.

In situation 2 the mass of the second body has been reduced (to 10). Thus the centre of gravity moves toward the larger body. The large body (M) will orbit the centre of gravity. Being much closer to the centre its orbit will be smaller than in situation 1. The smaller body (M) will now be much farther from the centre of gravity. Thus its orbit will be larger than in situation 1.

In situation 3 the mass imbalance is very one sided. The centre of gravity for both bodies will likely be not much different from the centre of gravity for the larger body. Thus the large body will orbit a point near its own centre. This will leave it with little orbit at all. The smallest body (m) will orbit the centre of gravity and is almost as far from that centre as physically possible. Thus its orbit will be nearly the largest it could possibly be.

To model the moon/apple situation I should properly add a situation 4. This is because I somewhat overestimated the effect a change in mass from moon to apple would have. The centre of gravity for the earth/moon situation is already very close to the centre of the earth. Changing the moon to an apple would only move that centre a few thousand kilometres.

So I think it's pretty clear cut that the orbit will change if we were to replace the moon with an apple. If I am somehow incorrect then I'd appreciate an explanation of exactly how that is. :)
 
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ThePhy

New member
situation 1:
M100----------X----------M100

situation 2:
M100--X------------------M10

situation 3:
M100X--------------------m1


M=Mass (of an orbiting body).
100/10/1=Arbitrary masses of orbiting bodies.
X=Common centre of gravity for two body system.

Here is why the orbit of the moon would change were it replaced with an apple.

Above we have three situations. In situation 1 two bodies of mass 100 (M100) are in orbit. They do not form a system where one orbits the other. Instead they both orbit a common centre of gravity (X). Just imagine each body being on the end of a T-section pole is being rotated at the red X. This rule applies in all cases.

In situation 2 the mass of the second body has been reduced (to 10). Thus the centre of gravity moves toward the larger body. The large body (M) will orbit the centre of gravity. Being much closer to the centre its orbit will be smaller than in situation 1. The smaller body (M) will now be much farther from the centre of gravity. Thus its orbit will be larger than in situation 1.

In situation 3 the mass imbalance is very one sided. The centre of gravity for both bodies will likely be not much different from the centre of gravity for the larger body. Thus the large body will orbit a point near its own centre. This will leave it with little orbit at all. The smallest body (m) will orbit the centre of gravity and is almost as far from that centre as physically possible. Thus its orbit will be nearly the largest it could possibly be.

To model the moon/apple situation I should properly add a situation 4. This is because I somewhat overestimated the effect a change in mass from moon to apple would have. The centre of gravity for the earth/moon situation is already very close to the centre of the earth. Changing the moon to an apple would only move that centre a few thousand kilometres.

So I think it's pretty clear cut that the orbit will change if we were to replace the moon with an apple. If I am somehow incorrect then I'd appreciate an explanation of exactly how that is. :)
You are now only 7 months late in describing center of mass considerations in this discussion. Next.
 

Stripe

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You are now only 7 months late in describing center of mass considerations in this discussion. Next.

Uh .. you were responding to my original analysis there.

Am I wrong?

You described my position as "technically correct" seven months ago, but you're still arguing with me. Why is that?
 

ThePhy

New member
Uh .. you were responding to my original analysis there.

Am I wrong?

You described my position as "technically correct" seven months ago, but you're still arguing with me. Why is that?
In what coordinate system do you claim the orbits will differ?
 

smalcat

New member
I am a bit reluctant to post, as I have not read the complete thread.

Of relativity, clocks and problems:

So it all started with Galileo, he first thought of relativity. It kind of goes like this: I am on a ship that relative towards the shore travel at certain speed lets say 5knots in one direction, and there is another ship that goes in the opposite direction also with the speed 5 knots. Both ships are on the same line (ie they will crash).

Galileo claimed, that if you are standing on the first ship, you can consider yourself standing still and the other ship crashing into you with the speed of 10 knots. Interestingly someone on the second ship can claim he is standing still and it is you who crashed into them with 10knots. Both are considered right in their claims, the observation systems are different.

Most people today accept this relativity and even take it for granted and even trivial.

There is one problem though. No matter how fast we move compared to a source of light, the speed of the light is the same. This we measure. There was no good theory that would explain that until the (special) theory of relativity.

So its not that we have observed some clocks to be slower than others, its that we have observed that light has the same speed, even if we are traveling with aprox 0.1% of the speed of light (30km/s) towards the source of the light. I would be extremely interested if anyone would try to explain why that is without using theory of relativity.




Some other random thoughts:
- each object (ie earth) has geostationary orbit, it is dependent on the objects mass and rotation, but until the mass of the satellite is comparably small not on the mass of its satellite
- if moon (moon is not in geostationary orbit) was switched with an apple there would be a change. Moon-Earth system circles around barycenter some 5000km from the center of Earth (= 1000km bellow surface), Apple-Earth system would circle almost at the exact centre of the earth. This difference of 5000km is rather small compared to the earth moon distance.
 

Lighthouse

Star-Spangled Kid
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I am a bit reluctant to post, as I have not read the complete thread.

Of relativity, clocks and problems:

So it all started with Galileo, he first thought of relativity. It kind of goes like this: I am on a ship that relative towards the shore travel at certain speed lets say 5knots in one direction, and there is another ship that goes in the opposite direction also with the speed 5 knots. Both ships are on the same line (ie they will crash).

Galileo claimed, that if you are standing on the first ship, you can consider yourself standing still and the other ship crashing into you with the speed of 10 knots. Interestingly someone on the second ship can claim he is standing still and it is you who crashed into them with 10knots. Both are considered right in their claims, the observation systems are different.

Most people today accept this relativity and even take it for granted and even trivial.

There is one problem though. No matter how fast we move compared to a source of light, the speed of the light is the same. This we measure. There was no good theory that would explain that until the (special) theory of relativity.

So its not that we have observed some clocks to be slower than others, its that we have observed that light has the same speed, even if we are traveling with aprox 0.1% of the speed of light (30km/s) towards the source of the light. I would be extremely interested if anyone would try to explain why that is without using theory of relativity.




Some other random thoughts:
- each object (ie earth) has geostationary orbit, it is dependent on the objects mass and rotation, but until the mass of the satellite is comparably small not on the mass of its satellite
- if moon (moon is not in geostationary orbit) was switched with an apple there would be a change. Moon-Earth system circles around barycenter some 5000km from the center of Earth (= 1000km bellow surface), Apple-Earth system would circle almost at the exact centre of the earth. This difference of 5000km is rather small compared to the earth moon distance.
You have already demonstrated that what we observe is wrong.
 

smalcat

New member
Well its true we live in a more miraculous world than we perceive, so for sure we are probably observing faulty. However, there is something peculiar about light.

The special theory of relativity is quite nice though. It for example predicts a different universe for different entities. An example: for light in this universe all the distances are 0. On the other hand, time spans into infinity. With other words for light everything is here and everything is eternal.

Physics kinda dont like this implication of the theory, which is rather strange as in other cases they are not above division by zero and other no-no mathemathical things.

So why do you believe we are observing it wrong?
 

Lighthouse

Star-Spangled Kid
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Well its true we live in a more miraculous world than we perceive, so for sure we are probably observing faulty. However, there is something peculiar about light.

The special theory of relativity is quite nice though. It for example predicts a different universe for different entities. An example: for light in this universe all the distances are 0. On the other hand, time spans into infinity. With other words for light everything is here and everything is eternal.

Physics kinda dont like this implication of the theory, which is rather strange as in other cases they are not above division by zero and other no-no mathemathical things.

So why do you believe we are observing it wrong?
For the very reason you posted about how it's observed speed never changes in relation to other objects, regardless of the other object's speed.
 

Stripe

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There is no practical difference between assuming gravity affects space and assuming gravity affects the instruments that measure space.

Simple, yet profound. :thumb:

If only the Darwinists would stop venting and think. Do they really care that much if there might be a better model out there than relativity?
 
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