Talk:Plumb line

Strictly speaking the plumb line is not straight: it is curved mainly in the North-South direction (approximately 0.2" per km of elevation). This is mathematically connected with the fact that gravity diminishes when going from pole to equator. The curvature is additionally affected by rough topography.

This makes no sense and definitely needs a source. —Keenan Pepper 22:43, 25 September 2006 (UTC)[reply]

It makes sense, following from the fact that the gravity of an ellipsoidical geoid is a nonhomogeneous vector field with divergent field line gradients (or something like that...) The number needs a source but the basic statement seems OK.

Right, but there's only one weight, and it's at the end of the string. As long as the weight of the string itself is negligible in comparison, the weight pulls the string taut, which means a straight line. It's only affected by the value of the gravity field at one point. Anyway, the main reason I removed it was because it lacks a source. —Keenan Pepper 05:16, 30 September 2006 (UTC)[reply]

>> "It's only affected by the value of the gravity field at one point."

Then the "The line has in every point the same direction as that of the force of gravity of the Earth" is wrong too. Femto 12:59, 30 September 2006 (UTC)[reply]

Regarding the proposed merge, this topic appears to be related more to the concept of "up" rather than to the tool, I'd merge into vertical direction instead, which incidentally already mentions non-straight verticals. Femto 14:20, 28 September 2006 (UTC)[reply]

I'm not sure I understand how you would arrange the redirects. You'd have Plumb bob as an article but Plumb line redirect to Vertical direction?? —Keenan Pepper 05:16, 30 September 2006 (UTC)[reply]

Yes, plumb bob about the tangible object, and plumb line a redirect to the abstract infinitesimal concept of directions in a vector field; judging from the Special:Whatlinkshere/Plumb line that's the primary use of this title. We must keep these two meanings strictly separate or run into contradictions like above. Those few redirects (if any?) that neither refer to the local direction of gravity, nor to the tool but specifically to its string, can use a disambiguated link like plumb line. Femto 12:59, 30 September 2006 (UTC)[reply]

Ah, that makes sense. But the original meaning of the phrase is the physical object, so it shouldn't be a redirect, but a disambiguation page. There's also another meaning in geometry, as a synonym of perpendicular. —Keenan Pepper 18:57, 30 September 2006 (UTC)[reply]

• Merge, no reason to have two articles. Luigizanasi 17:57, 28 September 2006 (UTC)[reply]
• Merge, as per above, and Plumb bob seems more appropriate — Graibeard ^(talk) 09:38, 29 September 2006 (UTC)[reply]