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Weak Equivalence Principle (WEP)

  1. Aug 2, 2009 #1
    As most of you probably know, the WEP states that the intertial mass and gravitational mass of any object are equal. This principle has base in Galileo's observations, that all free-falling objects have a constant acceleration. What I would like to get clear is the order of arguments that leads to this conclusion.

    My guess is that it went down like this:

    We know that
    [tex]F = m_i \cdot a[/tex]
    We also know that
    [tex]F_g = \frac{k \cdot m_g \cdot M}{r^2}[/tex]
    where k is a contant yet to be determined. We then have
    [tex]m_i \cdot a = m_g \cdot \frac{k \cdot M}{r^2}[/tex]
    We observe that a is constant, and therefore that
    [tex]m_i \propto m_g[/tex]
    Finally we set k = G (gravitational constant), so that [tex]m_i = m_g[/tex]

    Am I right? Is this 'the origin' of the value of G?

  2. jcsd
  3. Aug 3, 2009 #2
    the field produced by a massive body depends (by definition) only on its gravitational mass.
    the acceleration of a massive body within any given gravitation field depends only on its inertial mass and the strength of that field.
  4. Aug 4, 2009 #3


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    All free falling objects have the same acceleration.

    In Newtonian gravity, this is modelled by inertial mass being proportional to gravitational mass by a universal constant. In appropriate units, inertial mass equals gravitational mass.
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