The%20Newtonian%20equivalence%20principle

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The Newtonian equivalence principle

• It states that gravity is indistinguishable from
  any other form of acceleration.

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Roland Eötvös1848-1919

• Hungarian physicist.
• He studied the Earths gravitational field.
• He invented the torsion balance and showed that,
  to a high degree of accuracy, gravitational mass
  and inertial mass are equivalent.
• His work became a major principle of Albert
  Einsteins general theory of relativity.

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The torsion balance

• The torsion balance consists of two balls
  attached onto an insulating rod suspended from
  the middle by a thin wire. Eotvos used two
  spheres of identical mass but of different
  substances one of wood one of platinum.
• For Eotvos, any deviation from the
  proportionality of gravitating and inertial
  masses could be checked by detecting differences
  in the direction of the acceleration of different
  substances, and that those differences might be
  detected by rotations of a horizontal rod.

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• Therefore, if the magnitude of the Coriolis force
  (centrifugal force due to the Earth rotation) and
  gravity had been different for the two bodies due
  to their different compositions, Eotvos would
  have detected a twisting of the wire. None was
  seen.
• His experiment, performed in 1889, proved that
  the gravitational mass is proportional to the
  inertial mass up to 8 decimal figures ( not just
  4 decimals as was known before) accuracy of
  1/200 000 000.

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The torsion balance
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Measurements
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Robert Dicke1916-1997

• American experimental physicist.
• Dicke carried out a new experiment, using modern
  technology, and achieved an accuracy of 1/100 000
  00 000.
• He was able to increase the sensitivity, compared
  to Eötvös, in part by measuring the accelerations
  of their test masses to the Sun, rather than to
  the Earth. Any signal arising from the difference
  between gravitational an inertial mass would have
  the same 24hour periodicity as the the Earths
  rotation.
• It allows the signal to be discriminated from
  background perturbations, without disturbing the
  torsion fibre.

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• Works used
• www.kfki.hu/eotvos/onehund.html
• www.norskfysikk.no/nfn/epsbiografer/EOTVOS.PDF
• www.kfki.hu/eotvos/stepcikk.html