Where does the value of G come from in displacement experiments?

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Discussion Overview

The discussion centers on the origin of the gravitational constant G, specifically its numerical value of 0.0000000000667, and how it is derived from historical experiments and the choice of measurement units. Participants explore the implications of G's value in the context of physics and the universe.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that G represents the force between two 1-kilogram masses 1 meter apart, questioning the origin of its value.
  • Another participant argues that the value of G is a consequence of the arbitrary choice of units for distance, time, and mass, suggesting that in natural units, G could be considered unity.
  • A different participant clarifies that G should not be referred to as an "acceleration rate," contrasting it with "g," which is the acceleration due to gravity.
  • One participant speculates that G's value might be unique to our universe, proposing that different values could exist in other universes, and notes that G is one of the least accurately measured constants.
  • Another participant acknowledges the role of human-defined constants in determining G's value and seeks a layman's explanation of how these constants lead to the value of G.
  • A later reply suggests that G can be derived from Newton's law of gravitation and provides a link for further information.

Areas of Agreement / Disagreement

Participants express differing views on the nature of G and its measurement, with no consensus reached on the implications of its value or the best way to explain its derivation.

Contextual Notes

There are unresolved questions regarding the accuracy of G's measurement and the assumptions underlying the choice of constants used in its definition.

omin
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The magnitude of G is the same as the magnitude of the force between two masses of 1 kilogram each, I meter apart: 0.0000000000667.

Where does 0.0000000000667 come from?

G is an acclerlation rate. The experiments in my text from Henry Cavendish and Philip von Jolly. Both experients seem to only show a displacement rather than the time the displacement occurs. Wouldn't they have to know in the experiment the time the displacement occurs to get the constant G? If they didn't test for the time, how did they get it from the experiment?
 
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Well, not to be pedantic, but the numerical value of G is simply a result of mankind's arbitrarily-chosen units of distance, time, and mass. In many situations, physicists use natural units in which G (and other constants) are simply unity.

- Warren
 
To be even more pedantic: G is not an "acceleration rate", "g" is.
 
That really helpfull. I sit in a better place now. Thanks for the wonderfull explanation.
 
omin said:
Where does 0.0000000000667 come from?

That is a good question. Why is G the value it is?

Maybe it is the only conceivable value possible that would lead to a stable Universe where thinking lifeforms could evolve and wonder why G was that value!

Maybe in other Universes it has a different value?
It is one of the least accurately measured constants - only 6 significant figures I think...
 
I have misled things unintentionally in my first quesiton.

Humans have chosen distance, mass and time constants. These constants are used to define G, 0.0000000000667.

Is there an accessable to the laymen way, and brief way, to step through how we use our constants to arrive at 0.0000000000667?
 
omin said:
Is there an accessable to the laymen way, and brief way, to step through how we use our constants to arrive at 0.0000000000667?
It is found by application of Newton's law of gravitation. Perhaps http://www.npl.washington.edu/eotwash/gconst.html will help.
 
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