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Ross B
are 2 objects in the same frame if their centre of mass is stationary wrt each other?
Ross B said:u say "different frames" isn't it implicit in that statement one frame vs another?
Ross B said:if one frame cannot be distinguished from another
Ross B said:how do you know when to use a diff corrd system?
Ross B said:the book Serway 4th ed
Ross B said:I find this so confusing arent 2 objects in the same FOR if they are not moving relative to each other?
If you point the laser at the image of Earth that you see (you being in the Sun), you miss Earth by 16 minutes, or about 30000 km.Ross B said:so going back to my original post. If u are standing on the sun and you point a laser at where u think the Earth is will the laser miss the Earth as it is pointed at a false image which is 8 minutes behind where the Earth actually is ?
Ross B said:so going back to my original post. If u are standing on the sun and you point a laser at where u think the Earth is will the laser miss the Earth as it is pointed at a false image which is 8 minutes behind where the Earth actually is ?
Ross B said:there is no facility to edit yr post, like FB, so if u think of a bit u want to add us have to do an entirely new post?
Mister T said:There's nothing false about the image. Hold your hand as far away from your eyes as you can and look at it. You see it as it was about 3 ns ago, because it takes light about 3 ns to travel the length of your arm. Everything you see is a consequence of a real image forming on your retina.
If you lead Earth by 8 minutes when you aim, you'll still miss by 8 minutes because that's how long it will take for the laser beam to reach Earth, so as @SlowThinker points out, it's a total of 16 minutes.
Is this the situation you were pondering when you asked your original question? If so, a lot of frustration could have been avoided if you'd have mentioned that. Usually when people ask me a question I try to figure out why they're asking, because that helps me form a more meaningful answer. When we're really stumped on something we often don't know how to formulate the right question.
Sounds correct. Why do you have doubts, and why are you asking this in a Relativity section? Is this the first step to something else?Ross B said:If I lead the image of the Earth that is formed on my retina by 16 minutes I should get a reflection ...yeh?
Ross B said:as an outside observer of our galaxy (the Milky Way) is the Earth in the same frame as the galaxy?
Ross B said:as an outside observer of our galaxy (the Milky Way) is the Earth in the same frame as the galaxy?
Ross B said:if I point the laser at the image of the Earth that is formed on my retina I will miss it
Ross B said:If I lead the image of the Earth that is formed on my retina by 16 minutes I should get a reflection ...yeh?
Ross B said:If I note that angle and then gradually rotate the angle of the laser until I get a reflection.
I could just point it at the retina image each time, note the angle, rotate it (with a slight increment) note the angle and repeat ...that would work I think...until eventually I got a reflection ...it would be weird tho cos the reflection would be from, what would appear to be, empty space ...does that mean the laws of physics are not working in this frame as empty space is reflecting a laser ? and space that appears full (the retina image) is not reflecting a laser?PeterDonis said:Yes.
Yes.
It takes 16 minutes for light to make the round trip, so you won't be able to do this unless you rotate the laser very slowly--waiting for 16 minutes each time you move it a little bit, to see if there's a reflection, before moving it again. But during that time the Earth's image that you see is moving too, so you're not really gaining anything.
What? No. Why would you think that?Ross B said:it would be weird tho cos the reflection would be from, what would appear to be, empty space
I was told the following list of factsIbix said:What? No. Why would you think that?
You lead the Earth's apparent position by sixteen minutes when you send out your laser pulse. The pulse return time is sixteen minutes. Where will the Earth appear to be when the pulse returns?
If you don't lead a moving target, you miss it. This is not bizarre.Ross B said:1 if I fired the laser at where the Earth appeared to be, according to my retina, the laser would miss, and there would be no reflection, as the laser would miss...bizarre measurement 1
Why do you think the reflection would come from empty space? If you aim at the point where Earth will appear to be in sixteen minutes, where will Earth appear to be when the reflection comes back sixteen minutes later?Ross B said:2 if I fired the laser leading where the Earth appeared to be, according to my retina, by about 16 minutes (ie empty space) then the laser would reflect of the Earth so I would detect a reflection. From empty space!
It may be better to imagine a short laser flash rather than a beam, at least for now.Ross B said:bizarre measurement
Ibix said:No.
You seem to be bouncing all over the place. This thread isn't remotely about centre of mass, and it isn't even about the Earth in orbit any more, which at least was the topic of your other thread. Is there something you are trying to understand?
My point is that this:Ibix said:No.
is pretty much unrelated to what you were asking before. Why are you asking these questions? What is it that links these questions together? If there isn't anything you'd be better starting separate threads, since then people won't be trying to second guess what the link is. If there is a theme, it would help if you'd say what it is.Ross B said:yes given the above can I calc w?
Ibix said:I didn't miss it. You're asking two completely different questions. Yes, you can measure the speed of the Earth relative to the Sun. You cannot measure its speed relative to some arbitrarily chosen fixed point (which is what you now want to do), not without involving that fixed point somehow.
In short, you cannot ever measure the speed of something. You can only measure its speed relative to your measurement apparatus. If you'd left your apparatus behind when you fired your rocket, then you could measure the speed of the rocket. Or if you'd left a marker behind you could measure the speed of the marker from the rocket. But you cannot do it from inside the rocket because "speed" without the "relative to a specified thing" is meaningless.
I've answered this question twice already. Will you read my answer if I write it out a third time?Ross B said:Im not sure what yr answer is , is that a yes I can measure W or no I can't measure W ?
OK so that is a NOIbix said:I've answered this question twice already. Will you read my answer if I write it out a third time?