Wikipedia:Reference desk/Archives/Science/2023 May 5

= May 5 =

Coal merchant occupational diseases
I've just finished an article on coal merchants, once one of the most common businesses but now much rarer. The Dutch Wikipedia article on the topic is totally unsourced but mentions that back and shoulder injuries were common because of the backbreaking work of carrying heavy sacks. Does anyone know if there's a source on this to add? (Yes, I know about chimney sweeps' carcinoma, but I don't think it's directly relevant.) And of course any other sources to improve the article would be much appreciated. Blythwood (talk) 11:18, 5 May 2023 (UTC)


 * I don't have a reference but I would imagine hauling heavy sacks of anything could cause back and shoulder injuries and this is just stating the obvious. I doubt you need a reference for that. That said, black lung disease may be of interest. "It is common in coal miners and others who work with coal." (Referenced.) 41.23.55.195 (talk) 12:31, 5 May 2023 (UTC)
 * I know about You do need to cite that the sky is blue but gimme a break here. 41.23.55.195 (talk) 12:43, 5 May 2023 (UTC)


 * This article may be of interest (not sure how RS but it has a named author). Alansplodge (talk) 12:55, 5 May 2023 (UTC)
 * Not related to your question, but some images of coal merchants here, here, here and here. Alansplodge (talk) 17:45, 5 May 2023 (UTC)
 * Thanks so much to both of you! Will add the photos and that source. Currently thinking about a DYK hook. Haven't found a specific source for black lung in people delivering coal but might try looking further. Blythwood (talk) 19:47, 5 May 2023 (UTC)

Pendulum Motion
Suppose a pendulum consists of a rigid slender rod. As the pendulum swings downward, the points closer to the free end of the rod are moving faster than the points closer to the fixed end, but all of the points are being accelerated by gravity at the same rate. I understand that gravity provides a torque about the fixed end, but somehow I can't intuitively understand what's allowing the points to have different speeds.  Puzzledvegetable Is it teatime already?  21:43, 5 May 2023 (UTC)
 * The gravity is applying a force to each part of the pendulum. But because it is rigid, there are forces withing the material called stress. This mostly counterbalances the force of gravity. It varies in strength and direction in different parts of the pendulum at different phases of the swing. Graeme Bartlett (talk) 21:50, 5 May 2023 (UTC)
 * Since the pendulum is a rigid body, gravity can be simplified to acting at the centre of mass. For a uniform rod this will be in the centre of the rod.  Neglecting air resistance (probably not a valid assumption for a rod), then gravity acts on this centre and will vary from a maximum when the rod is horixontal to a minimum when it is vertical. Martin of Sheffield (talk) 22:12, 5 May 2023 (UTC)
 * The reason, though, this simplification can be made is due to forces acting within the rigid body, as indicated above by Graeme Bartlett. These internal forces counteract the effect of external forces (such as gravity) that threaten to shear it apart. If the stress (in the pendulum case more specifically the tension) exceeds a certain limit, it will still come apart. --Lambiam 06:29, 6 May 2023 (UTC)
 * A related "real world" example of gravity acting on a rigid body anchored at one end is the popular "falling chimney" problem in intro-physics courses. Can't find a WP article about it. DMacks (talk) 23:31, 8 May 2023 (UTC)
 * If both are modelled as homogeneous straight rods of constant thickness, the equations for the pendulum and chimney are identical (until the chimney hits the ground). In practice, the chimney comes apart before it hits the ground, since the bound between the bricks cannot withstand the tension. --Lambiam 21:01, 9 May 2023 (UTC)