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Recent measure of G constant

  1. Jun 23, 2015 #1
    Has there been any recent changes in the G constant value?
     
  2. jcsd
  3. Jun 23, 2015 #2
    I meant in the official value of G known to us?
     
  4. Jun 23, 2015 #3

    SteamKing

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    Since G must be determined experimentally, there will be some variability in its reported value.

    This article, Ref. 9, contains a report on the latest measurements of G:

    https://en.wikipedia.org/wiki/Gravitational_constant
     
  5. Jun 23, 2015 #4

    D H

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    The job of the CODATA Task Group on Fundamental Constants is "to periodically provide the scientific and technological communities with a self-consistent set of internationally recommended values of the basic constants and conversion factors of physics and chemistry based on all of the relevant data available at a given point in time."

    Updates are released every four years. This update will be published online at http://physics.nist.gov/cuu/Constants, supposedly in May or June 2015, but that hasn't happened yet. That site still has the CODATA 2010 values. It's still June 2015, so nominally this should any day now -- or maybe not.
     
  6. Jun 23, 2015 #5
    G cannot be a constant since the mass of the Earth is not a constant.
    In fact several tonnes of micrometoric dust is accumulated every day.
    Although that makes no significant difference to the measure of G over the course of a human life time, it might make a difference on geologic time scales.
     
  7. Jun 23, 2015 #6

    SteamKing

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    This just means that GMearth varies slightly over time.

    The variation in G over longer time scales has been studied using astronomical phenomena:
    from the Wiki article linked above.
     
  8. Jun 23, 2015 #7

    D H

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    You are confusing G, the Newtonian gravitational constant, with g, gravitational acceleration at the surface of the Earth. Big G is dimensional physical constant, the G in [itex]F=\frac {Gm_1m_2}{r^2}[/itex] (Newton's law of gravitation). That is modern notation; Newton himself didn't express his law of gravitation that way, nor did Henry Cavendish, the first to measure G (but only after the fact). Cavendish intent was to "weigh the Earth".

    Measuring G is extremely non-trivial. It is the least well known fundamental physical constant.
     
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