If photon is mass-less why can it be pulled into blackhole?

Discussion in 'Physics & Math' started by Saint, Aug 7, 2017.

  1. The God Valued Senior Member

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    Nothing I said is proven wrong.
    You are just joining the bandwagon as if eureka moment for you that lo The God is proved wrong. Just highlight a single line from this thread which proves me wrong. I challenge both you and James R. Leave aside the other three who could not explain simple momentum transfer even in 100 odd posts.
     
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  3. DaveC426913 Valued Senior Member

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    This is wrong.



    Also, this thread is about capture and escape in orbital mechanics. Please take your inflammatory sidebar elsewhere.
     
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  5. The God Valued Senior Member

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    Ref post #138 again, three possibilities are shown. And it is not wrong, it is wrong in your mind only because you do not understand what Gravitational capture means.


    Read the wiki link, you should start from that...

    https://en.m.wikipedia.org/wiki/Asteroid_capture

    Come back after reading this and if you have learnt something you will retract your statement, and if you have not learnt anything then let me see what strawman you give.
     
    Last edited: Aug 20, 2017
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  7. The God Valued Senior Member

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    Kittamaru,

    I object to Kittamaru public assertion that I am wrong in infraction comment. I am not questioning his infraction but he made an unsupported statement about my being wrong, he should prove which statement of mine is wrong otherwise retract. Does he have the guts or civility which he is attempting to preach?

    It is shocking that he is swayed by James passing comments and without evaluating made a poor comment. James siding with individual was in bad taste, he should have given his opinion on the subject, James fuelled the hostility which was otherwise tamed, he must resign, due to his part time interest, he cannot do justice to super mod post. He is promoting favouritism too.

    I standby my challenge if James or Kittamaru can pin point a single incorrect statement.
     
  8. The God Valued Senior Member

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    3,546
    That's the problem with you. You do not follow the full thread and start making half understood biased comments.

    The word propulsion was used by DaveC not me. He also made a statement that no natural body can escape from the surface of a planet, I gave him this photon example.

    He made another assertion that a body cannot be captured in orbital motion in 2 body system, I gave him photon capture and orbital motion around black hole.

    It is clear that either you are ignorant like DaveC on this or you just did not read the relevant posts. To me it appears the former is true.
     
  9. exchemist Valued Senior Member

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    6,289
    I'm reporting all these ridiculous, vexatious and offensive posts of yours. I don't know what's got into you, but whatever it is, it spoils the thread for everyone.
     
  10. DaveC426913 Valued Senior Member

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    Did you read it?

    1] They don't say any body; they say planetary body.

    "Asteroid capture is the entering by an asteroid into an orbit around a larger planetary body.*** (link) to defintiion "

    They then define a planetary body - just for your benefit:

    ***"A planetary body or planetary object is any secondary body in the Solar System."

    i.e. there are more than just the two objects in the scenario.



    2] And notice, no mention of the primary body (the Sun) as a capturing agent, as was your assertion. (The sun can capture a body, but it still requires a third mass to steal the asteroid's energy at just the right moment.)


    3] Point of order: People who have facts don't need to troll to get their point across; they can simply state facts, civilly, as others have been doing. Trolling is a deliberate distraction tactic, designed to draw attention away from weak or erroneous assertions. It's a dead-giveaway. I'll engage you as long as (or if) you stay on-topic and remain civil.
     
    Last edited: Aug 21, 2017
  11. Confused2 Registered Senior Member

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    I need guidance on this point. If two bodies of (say) equal mass approach with a trajectory that will lead to one (or both) retracing its path (to a fair approximation) then the gravitational interaction will lead to an exchange of momentum which will result in a departure speed that is:-
    1) The same as the speed of arrival.
    2) Less than the speed of arrival.
    3) Greater than the speed of arrival.

    Far be it from me to suggest what the consequences of alternative 2) might be.
     
  12. DaveC426913 Valued Senior Member

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    6,604
    It is simpler than that.

    If any two bodies (of any mass) approach each other (and do not collide), both will exit each other's sphere of influence with the speed (relative to each other) with which they entered (though the angle will most likely be different). Again, for The God's benefit: what you described is a two-body scenario.

    I'm not sure that answered your question re: "retracing its path".
     
  13. Confused2 Registered Senior Member

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    424
    Suffice it to say that it failed to convince me.
     
  14. Confused2 Registered Senior Member

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    Shaken but not stirred.. Make one mass M and the other 3M ... in the exchange of momentum M1 loses .. and M3 gains v/3 ... and the parting velocity is
    1) The same as the speed of arrival.
    2) Less than the speed of arrival.
    3) Greater than the speed of arrival.
     
  15. DaveC426913 Valued Senior Member

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    2. Same.

    At some distance X, pointM1X1, pointM2X1, they each have a combination of gravitational potential energy and kinetic energy. As each falls toward the other, it converts g-pot energy into kinetic energy. Then as each rises away from the other, it converts the kinetic back to g-pot energy at the same rate. This is conservation of momentum at work. When each arrives again at distance X (pointM1X2, pointM2X2), each has exactly the same g-pot energy and exactly the same kinetic energy as when it started.

    Notice also, by the way, that this is symmetric. You can reverse the procedure - start each at their respective pointsX2 - and it each follow exactly the same path backwards to point X1.

    The upshot of that shows that, not only can a falling body not be spontaneously captured into an elliptical orbit, but that an orbiting body cannot be spontaneously ejected into a hyperbolic trajectory.
     
    Last edited: Aug 21, 2017
  16. Confused2 Registered Senior Member

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    We have to choose the same inertial frame for before and after. It certainly isn't symmetrical before and after because (in my retrace path scenario) when m1 returns to (near) its starting point I think you'll agree that (transfer of momentum) has caused M3 to be heading away for some time. When M1 gets back to the same point in my fixed inertial framework the attraction to M3 is lower (M3 has been moving away at v/3). Does V_m1 compensate for this ... same question again.
     
  17. DaveC426913 Valued Senior Member

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    I think having both bodies moving is complicating matters. If we increase M1's mass by many thousands-fold, we can treat it as essentially motionless, then examine what happens to the smaller mass. knowing that, in actuality it applies to both.
     
  18. Confused2 Registered Senior Member

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    424
    We could on an engineering forum - but this is the physics section of a physics forum.
     
    The God likes this.
  19. The God Valued Senior Member

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    3,546

    So, then for sun you will talk of milky way center and make it 3 body.

    The capture by a planet (of astroid) depends on initial conditions of astroid as explained in my multiple posts, but you are crying hoarse that it requires 3 body. There is no such need. You do not understand binary systems, you are just catching words here and there.

    Although you try to be scientific mind, but unfortunately you failed here.

    Both the assertions of DavC in #1 and #4 as taken up by me were wrong. He is just wriggling out.

    And James R does not know that a photon may be massless but it has momentum, there is a momentum Conservation when a photon is emitted from a body, a process quite similar to propulsion. I objected to his casual nonsense.

    But unfortunately this site has been reduced to pure lay site where none wishes to go beyond the very basic. Where likes of DaveC are experts with no understanding of orbital mechanism.

    you are foolishly stuck in this 2 body 3 body N body nonsense. The key here is when they "approach", that means they will be having certain initial conditions like velocity vector etc. Was it not explained to you? You were confusing W4U that for escape the angle does not matter, it matters because that's the part of 'approach'.

    So what if it is complicated? Answer, why are you dodging after making 2-3 unsuccessful attempts ? Or say you are not equipped to answer this beyond a point, others may take up, then I will invite Kittamaru.
     
    Last edited by a moderator: Aug 21, 2017
  20. The God Valued Senior Member

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    When two bodies "approach" each other....as put up earlier by me one of the three could happen.

    1. They collide.
    2. They get into orbital motion.
    3. They pass by.

    DaveC feels that #2 cannot happen, and he is supported by few others too. But they are all propagating bad science, and now they will get into straw man.

    Your focus is #3, a very relevant question, and it has generalized solution which will cover frame of reference, gain in momentum, loss in momentum (due to gravity assist....we may not know about the central force acting on these two objects, thus making it a real complex problem. Wish it was as simple as an electron moving at very high speed near a moving heavy positive charge.
     
  21. uhClem Registered Member

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    15
    In the “retrace path” you have to view it as extending back to t=-infinity and forward to t=+infinity. The model is also an infinite universe with no other bodies anywhere. In the model “not captured” means the initial starting point at t=-infinity is infinitely far away and has some “excess” radial velocity. The “excess” radial velocity at system escape t=+infinity has to be the same as the initial t=-infinty “excess” radial velocity. So the answer is as DaveC says, the same. The moving body starts with maximum potential energy which is converted by gravity to kinetic energy which is maximum at closest approach and then the kinetic energy is transformed back into potential on the outgoing leg. Energy is, as Dave said, conserved and the whole thing is symmetrical. If the initial excess velocity is non-zero and toward the center, then the path is hyperbolic. If the initial excess velocity is exactly zero the path is parabolic. The only other scenarios (circle and ellipse) do not “start” at an infinite distance away (t=-infinity). System are always in a captured state, or always in an non-captured state. They either start and end infinitely far away, or they don’t. Capturing (starting free and ending captured or vise versa) is not a thing in a 2-body problem.

    Angular velocity is also conserved. Whatever the angular velocity is at t=-infinity, it ends at t=infinity with the same. It does seem like because the entrance and exit angles are not 180 degrees apart that the central object might gain some lasting kinetic energy, but that is just all in our heads.

    I want to add that I was wrong in my first post about the reference frames. I am a bit rusty at this. I knew that falling bodies are an inertial frame of reference but failed to apply that knowledge in this situation because of a brain malfunction. DaveC and exchemist were right about there being a frame of reference for each body in the system. Those are inertial frames and natural choices for the problem.
     
    Last edited: Aug 21, 2017
  22. Kittamaru Now nearly 40 pounds lighter. Staff Member

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    13,025
    You may object all you like - it doesn't change the fact that you have been refuted. Case in point - you are still confused about what it takes for an object to be captured into orbit around the Sun.

    Kindly point out where DaveC said that two bodies CANNOT end up in an orbital situation - what I read from his posts is that it was highly unlikely for an object on a trajectory that would see it pass through the system to wind up being captured without something else acting upon it to alter said trajectory/velocity to result in a capture (such as what happened with Apollo 11). Don't try to attribute things to people that they haven't actually said.
     
  23. The God Valued Senior Member

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    Bland statement devoid of any supporting evidence. You are too good in writing lengthy posts quoting from here and there. Why dont you pin point which statement of mine is incorrect?


    1. It's wrong to say that angle of approach does not matter.
    2. It's wrong to say that an object cannot be captured in orbital motion. It all depends on initial conditions.
    3. It's wrong to say that since photon is massless no propulsion type mechanism is involved.
     

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