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O/T What is the speed of gravity?

Discussion in 'Off Topic Threads' started by joe kuhn, Mar 23, 2013.

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  1. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    This is an interesting question to me because we live in gravity all our lives and don't have any experience with it turning on and off. It's just there when you wake up in the morning and seems to be instantaneous. Gravity is 'on' all the time. So how long does it take for gravity to have it's pulling effect on things nearby?

    If the moon were to magically disappear it would take 1.5 seconds for the last light from it to reach earth and then there would be no more moon to see.

    How long would it take for the tides to start flattening out?

    Again, how long does it take for the gravity of the moon to reach earth? Would it be instantaneous, as soon as the moon disappears from view, or a while after the moon can no longer be seen?
     
  2. hmb

    hmb Well-Known Member

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    Trap shooters do not have sufficient cranial capacity to understand this concept. HMB
     
  3. rpeerless

    rpeerless Well-Known Member

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    "Newton's law of universal gravitation states that the attractive force F between two bodies of masses M1 and M2 separated by distance d is F=GM1M2/d2 where G is the Universal Gravitional Constant (6.67 x 10 to -11 power Nm2kg to the negative 2 power) The force of gravity on the earth ia a special case of all attraction between masses and causes bodies to fall toward the center of the earth with a uniform acceleration g = GM/R squared where R and M are the radius and mass of the earth."

    ref: New American Desk Encyclopedia

    Does that help?
     
  4. oz

    oz Active Member

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    gravity is not a velocity...It is a force.
     
  5. Shooting Jack

    Shooting Jack Active Member

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    It really relates to how high you are when you fall and how old you are. The older you are the faster you hit the ground and with more impact. Jackie B.
     
  6. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    "...since general relativity specifies the detailed mechanism by which gravity works, it provides a mathematical framework for determining how fast it transmits its influence. The speed of transmission comes down to the question of how fast the shape of space can change in time...He (Einstein) found that warps and ripples-gravity, that is-do not travel from place to place instantaneously, as they do in Newtonian calculations of gravity. Instead, they travel at exactly the speed of light."

    "If aliens plucked the moon from its orbit, the tides would recede a second and a half later, at the exact same moment we'd see that the moon had vanished. Where Newton's theory failed, Einstein's general relativity prevailed."

    Page 71-72, "The Fabric of the Cosmos", by Brian Greene.

    So light, magnetism, electricity and gravity all move or have an effect at the same speed: 186,000 miles per second. Why all the same?

    barfin got it right away, and did a cart wheel to celebrate, but oz my friend - even though gravity is indeed a force, it can have an effect with a certain speed. Jackie and I have been enthralled with the effects of gravity for a while now.
     
  7. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    No snow but too cold to shoot, yes.

    rpeerless - question had to do with how fast gravity would begin to have an effect on a body - to make it start to fall, if the earth were instantly created in a flash, for example, rather than how fast the object itself would fall towards the earth. Trick question people normally don't even consider. At least I hadn't until I read about it. I had no basis for making a guess.
     
  8. rpeerless

    rpeerless Well-Known Member

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    Wow, Joe!
    (Wish I could do back flips like that!)
     
  9. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Takes practice. Gravity is tricky you know.
     
  10. Steve W

    Steve W Well-Known Member

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    Can you ask something simple on Saturday? I had enough questions to answer during the week.

    And college was 30 years ago. :-(
     
  11. halfmile

    halfmile Well-Known Member

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    It's a hell of a lot faster in the neighborhood of Jupiter.

    HM
     
  12. Mike Battista

    Mike Battista Well-Known Member Supporting Vendor

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    From my skydiving days 16 feet per second / per second until terminal velocity is reached. That being predicated upon air density and resistance.
    Mike Battista
     
  13. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    There seems to be some confusion between:

    1. The speed of a objects falling towards earth.

    And

    2. The speed with which gravity reaches out effects other objects, which is the speed of light.

    Some of you are talking about the first, which is great. It's important to know that in certain applications like sky diving you fall at rate X and need to pull that chute open by time Y. Heh.

    I'm referring to the second which is 186,000 miles per second.

    If you were floating freely in space and the earth was suddenly created 186,000 miles from you, it would take 1 second for gravity to reach you and begin pulling you towards earth. The speed with which you began moving towards earth is not what I'm asking about. I'm talking about how gravity actually moves through space at a given rate and then begins to have it's effect. It's a subtle difference conceptually but the difference in the numbers is huge.
     
  14. wayneo

    wayneo Active Member

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    Mike, I thought it was 32 ft. per second/per second?

    Wayne
     
  15. grnberetcj

    grnberetcj Active Member

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    For those that paid attention in school!!

    Curt


    [​IMG]
     
  16. Bvr Tail

    Bvr Tail Well-Known Member

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    Hey, I resent that, Curt!


    I did pay attention in school, and finally got her phone number, and address, but my attention span soon shortened with the presence of her big brother.


    Wow, was life simpler then.
     
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