Talk:Standard gravity

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[edit] Is this true?

The article says that "the value of G can be measured precisely", but my understanding is that, compared to other physical constants, G is actually rather difficult to measure precisely and is not known to a great degree of accuracy. Is the statement in the article just wrong, or am I misunderstanding something? Matt 01:47, 27 April 2007 (UTC).

g is fairly easy to measure precisely, using the frequency of a long heavy pendulum or whatever. At our physics building they have an accurate value of g measured in one of the lecture theatres. 213.48.15.234 13:23, 18 May 2007 (UTC)

g is easy to measure. G is hard. --Reuben 22:44, 25 May 2007 (UTC)

I have changed the offending section to make it clear that G is rather difficult to measure precisely. Matt 01:36, 27 May 2007 (UTC)

In fact, I have now moved that whole section to Earth's gravity. Matt 02:35, 27 May 2007 (UTC)

"For a planet R will be the planet's radius and z will be the distance from the centre of mass to the object (z ~ R) while for an accretion disk around a celestial body like a black hole R will be the distance to the black hole, and z the distance above the accretion disk." This is confusing and needs better explanation. I assume "z ~ R" means z is approximately equal to R? Why approximately? What is the geometry of an "accretion disk" and how does this relate to the formula? 199.46.245.230 (talk) 00:12, 15 February 2008 (UTC)

Yep, approximately. 69.143.226.129 (talk) 03:23, 23 February 2008 (UTC)

[edit] Dubious

The value of g0 defined above is an arbitrary midrange value on Earth...

I find it hard to believe that the value of 9.80665 is "arbitrary". Surely all those decimal places weren't plucked out of thin air? At http://home.att.net/~numericana/answer/units.htm#g it says:

To an actual measurement of 9.80991 m/s2 in Paris, a theoretical correction factor of 1.0003322 was applied which gives a sea-level equivalent at 45° of latitude. The result (9.80665223...) was rounded to five decimals to obtain the value officially enacted by the third CGPM, in 1901.

This explanation sounds far more likely to me, but I can't find any other sources to back it up so I haven't yet changed the article. —Preceding unsigned comment added by 86.134.72.74 (talk) 19:25, 25 April 2008 (UTC)

[edit] explanation of units

I've never heard accelerations being described in terms of "square seconds." The phrase "per second per second" sounds a lot more meaningful. I'm having trouble even conceiving of square seconds because a number of seconds isn't a distance. Arithmetically, yes, it makes sense, because to arrive at the correct number, the seconds quantity has to be multiplied by itself. Joe (talk) 20:00, 18 May 2008 (UTC)