Shine a laser perpindicular to ground

Discussion in 'Science' started by Pianist, Jul 19, 2008.

  1. Pianist

    Pianist Member

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    Hey guys,

    I was thinking that lets say i shone a laser perpendicular to the earths surface at that point, would the beam just carry on forward into space or would it curve around the earth and hit me in the back?

    The diagram explains what im trying to say

    Thanks

    [​IMG]
     
  2. scottath

    scottath Member

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    My Yr 11 knowledge of last terms phyics is helpful.....WOW

    In Theory it would be the second option of continuing of in a straight line - but particles in the atmosphere and the atmosphere itself would refract the light so it would curve a little before going straight again - but will still leave the atmosphere in a straight line

    Make sense?
     
  3. -KoMoD0-

    -KoMoD0- Member

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    It will go straight :thumbup:
     
  4. pippin88

    pippin88 Member

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    Do you perhaps mean parallel to the earth's surface?
     
  5. SLATYE

    SLATYE SLATYE, not SLAYTE

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    As above, it'll go roughly straight. The atmosphere and Earth's gravity will cause a tiny bit of curving, but it certainly won't curve around to hit you again.
     
  6. OP
    OP
    Pianist

    Pianist Member

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    yeah, to the flat surface that im standing

    ok so it bends a little bit, if the earth was bigger say as big as the sun, would it curve along the surface or still continue straight?
     
  7. scottath

    scottath Member

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    Same as before - small curve.

    If you were to do it on the sun though [assuming you survived] i would say it would go straight - as the sun has no atmosphere.
     
  8. -KoMoD0-

    -KoMoD0- Member

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    Gravity will affect it but we are talking about tiny tiny variations here, nowhere near a curve.
     
  9. scottath

    scottath Member

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    Also have refraction of the light when hitting particles [water vapour etc] in the atmosphere
     
  10. OP
    OP
    Pianist

    Pianist Member

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    so would the planet have to be light years in diameter for the light to bend around and come back?

    are there any formulas for calculating photon interactions with gravity?
     
  11. -KoMoD0-

    -KoMoD0- Member

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    Wait for Goth to show up, he is the physics genius :)
     
  12. scottath

    scottath Member

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    Very unlikely that the light would bend around at all - Actually probably impossible

    ????? I'm only in Yr11....so no idea - i would guess there is but the particles in the atmosphere would through it off - so if you went to a planet the same size as Earth but with no atmosphere the it would work [the gravity calcutlation - not the bend around the planet bit...]
     
  13. Whisper

    Whisper Member

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    No

    Just very massive, as in, has a lot of mass.

    Think black holes or neutron stars

    Actually, its not really possible to observe something that is capable of bending light back in the way you are describing.
     
  14. hlokk

    hlokk Member

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    edit: light is affected by gravity (or more accurately curved space-time which is what gives the illusion of gravity), so it is possible

    The only way something would come full circle would be if you matched the speed to the orbital speed at that location (i.e. height). The speed is the square root of the gravitational parameter divided by the radius. The radius in the case of a light object (compared to the earth, as a heavy one would shift the orbit point) would be from the center of the earth to where the projectile left. Thats for a circular orbit, you could get elliptic orbits or whatever, which would hit you as well, but a little more complicated.
    (We'll assume no atmosphere and no rotation of the planet as you would have moved some amount by the time it made one revolution).


    Could you somehow be in space around a large object and fire a laser such that it orbits and hits you? Yes.

    Basically you need to be on the photon sphere. This is a sphere where tangential photons will orbit. You would find one around a black hole (1.5 times the radius of the event horizon radius, or swartzchild (sp?) radius). It is possible to have other non-black hole things do this such as a neutron star. I dont think you could stand on the surface though, as a planet made of atoms would have is diameter larger than the photon sphere radius (afaik). If you could stand on a pole (figureatively) jutting out of a suitable sized neutron star, or had a jetpack near the star or a black hole you could.


    edit: try some orbits here: http://www.mofunzone.com/online_games/orbit.shtml#
     
    Last edited: Jul 19, 2008
  15. scottath

    scottath Member

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    That sort of made sense....

    Thanks for the impossible in site into life of a laser beam on a object we haven't yet reached.

    Seriously - that was interesting and very technical - thanks for the lesson

    EDIT: cool game :)
     
    Last edited: Jul 19, 2008
  16. hlokk

    hlokk Member

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    Theres another game where you attack other people with gravity influenced rockets which is fun, and theres also a small java applet where you can create as many objects as you like at the same time, and you can wait for the bad orbit ones to weed themselves out.

    Keep in mind, the speed of light is fixed if you're playing the game while thinking about light (also, the masses would all be black holes or something)
     
  17. Menthu_Rae

    Menthu_Rae Member

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    What the hell do they teach you kids in school these days? :p edit: added the tongue so it sounds like it should (i.e. not too serious)
    http://en.wikipedia.org/wiki/Corona

    http://en.wikipedia.org/wiki/Photosphere

    http://en.wikipedia.org/wiki/Chromosphere

    http://en.wikipedia.org/wiki/Solar_transition_region

    http://en.wikipedia.org/wiki/Stellar_atmosphere
     
    Last edited: Jul 19, 2008
  18. scottath

    scottath Member

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    Whoops - your right

    Havent been there for 2 weeks any how - in holiday mode.....:confused::D:confused:
     
  19. Menthu_Rae

    Menthu_Rae Member

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    Yeah yeah and I haven't been there for 5 years :lol:

    Anyway it's all good mate - even though it didn't sound like it - my post was kind of tongue in cheek.

    Was just letting you know that it does indeed have an atmosphere, albeit completely unlike our own ;) :thumbup:
     
  20. scottath

    scottath Member

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    By atmosphere ealier i was refering to the particles in ours - like water vapor, CO2 etc that can/will refract the light of the said lazer

    No offence taken -
     

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