A determination of the Newtonian gravitational constant on a scale of ten metres

Moore, Gary Ian (1986). A determination of the Newtonian gravitational constant on a scale of ten metres PhD Thesis, School of Physical Sciences, The University of Queensland. doi:10.14264/uql.2015.36

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Author Moore, Gary Ian
Thesis Title A determination of the Newtonian gravitational constant on a scale of ten metres
School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
DOI 10.14264/uql.2015.36
Publication date 1986
Thesis type PhD Thesis
Supervisor Unknown
Total pages 166
Language eng
Subjects 040405 Gravimetrics
Formatted abstract
A sensitive vacuum beam balance has been developed and used in an experiment to determine the Newtonian gravitational constant, G, on a scale of ten metres. The balance is used to weigh the gravitational forces exerted by layers of water, on 10 kg masses suspended (in evacuated tubes) at different levels in a hydro-electric pumped-storage reservoir.

A preliminary value of

 G = (6.668 +/- 0.040) × 10-11 m3 kg-1 s-2

has been obtained and stronger constraints have been placed on proposed departures from the gravitational inverse square law over the range 2 m to 20 m than were previously available from laboratory scale experiments.

Angular displacements of the balance arm are sensed using the technique of capacitance micrometry which is sensitive to displacements as small as 10-7 of full scale. The balance arm is servoed to a null by means of a voltage applied to one of two electrostatic deflection electrodes. Independence of the null position from tilt of the surroundings is achieved by servoing the entire balance assembly relative to the local horizontal defined by a mercury level reference. Measurements are made in terms of the deflection voltage required to restore the balance arm to the null position. The balance is sensitive to changes as small as 3 parts in 1011 in the weight of a 10 kg test mass. This sensitivity would allow a measurement of the effect of a ten metre layer of water and hence a determination of G with an accuracy of 3 parts in 105. This accuracy exceeds that of current laboratory determinations. However vibration of the supporting pylon and imperfect servoing of the apparatus to horizontal currently reduce the accuracy of individual weighings to about 3 parts in 109. Suggestions for improvements are made which should lead to about a factor of ten increase over the current accuracy, even allowing for the vibration problem.
Keyword Gravitation
Additional Notes Other Title: Newtonian gravitational constant.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Mon, 05 Jan 2015, 14:54:02 EST by Mary-Anne Marrington on behalf of Scholarly Communication and Digitisation Service