Wikipedia:Reference desk/Archives/Science/2022 March 9

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March 9

Rusting in building rods

If rainwater falls on the roof of old homes, then there are cracks in the concrete due to rust in the iron rods.

See these images

https://i0.wp.com/civilblog.org/wp-content/uploads/2015/07/Repair-of-corroded-reinforced-concrete-ceiling.jpg?resize=320%2C240&ssl=1

https://happho.com/wp-content/uploads/2017/06/Corrosion-of-Steel-due-to-improper-Cover.jpg

You know that if there is hollow on the wall or roof(If there is space between bricks and concrete plaster) if you hit it makes a different sound, indicating it needs to be repaired, as if the concrete is attached firmly on the body then it won't make any hollow sound, as empty cans make different sounds than filled cans if you hit the surface.

In my case, the concrete of the roof didn't fall like those pictures, but some cracks appeared, due to a hollow sound, I found rust has formed. Now a mason removed the broken concrete completely, removed the rust from the rod, and plastered it with new concrete. There is an extra tin shade that stops rainwater from falling on the roof. After three years I see that cracks appeared again, but this time it is in a small area, and the hollow sound is also less severe.

Now I want to know can the rods which had rusted, develop rust without access to water and air?

The chemical reaction of rusting needs moisture; without it, iron will not rust. If the iron is in contact with outside air, moisture can form by condensation from moist air.  --Lambiam 07:10, 9 March 2022 (UTC)

There's more discussion of this in Reinforced concrete#Common failure modes of steel reinforced concrete. Mike Turnbull (talk) 10:35, 9 March 2022 (UTC)

Oxide jacking (an article that I largely wrote) also discusses this type of problem. Cullen328 (talk) 20:39, 9 March 2022 (UTC)

Language in Palladium

Is this grammatically correct language for scientists, or perhaps American scientists?

Palladium is a key component of fuel cells, which react hydrogen with oxygen to produce electricity, heat, and water.

To my non-scientific and British English ears, that use of "react" is gratingly incorrect, and perhaps could be "which use a reaction between hydrogen and oxygen", but I didn't want to edit without checking on my own WP:WORLDVIEW ignorance. --Dweller (talk) Old fashioned is the new thing! 09:27, 9 March 2022 (UTC)

To my British ears, I'd agree. Go for it: be WP:BOLD. Martin of Sheffield (talk) 09:35, 9 March 2022 (UTC)

This agrees, but this does not. So this looks like an WP:ENGVAR thing which I think would be resolved by your proposed wording, as per WP:COMMONALITY. Bazza (talk) 09:57, 9 March 2022 (UTC)

• Er, read it again. In the first "This" page, it's sense 2.1. In the second, it's sense 1.4. Not that there's anything wrong with Lambiam's suggestion below. --184.144.97.125 (talk) 23:32, 9 March 2022 (UTC)

Shorter: "in which hydrogen and oxygen react".  --Lambiam 11:08, 9 March 2022 (UTC)

I agree. Philvoids (talk) 11:26, 9 March 2022 (UTC)

Thanks all. Adopting Lambiam's elegant precis. --Dweller (talk) Old fashioned is the new thing! 12:29, 9 March 2022 (UTC)

Did they mean catalyzes? As in it's not just an inert container? Sagittarian Milky Way (talk) 18:16, 9 March 2022 (UTC)

Yes. See fuel cell. --184.144.97.125 (talk) 23:33, 9 March 2022 (UTC)

I don't care if something is grammatically 'incorrect' or awkward, but there should be no chemical ambiguity. I would interpret the phrase as '[Paladium] which react with hydrogen and oxygen' . I don't think ' Paladiumm reacts with H and O' means anything other than ' a P, H and O reaction'. There's no actor and subject in a reaction.--TZubiri (talk) 16:06, 10 March 2022 (UTC)

The agent corresponding to the verb form "react" in the original sentence is "fuel cells", not "Palladium". And the agent does not react "with" chemical substances; the verb is transitive here.  --Lambiam 19:43, 10 March 2022 (UTC)

wiktionary has both an intransitive and transitive sense for chemistry (senses 3 and 4) which sounds what this distinction is. It doesn't say if the transitive sense is uncommon in Brtish English. RJFJR (talk) 03:27, 12 March 2022 (UTC)

If a train needs x watts to sustain y mph on a perfectly banked circle will it need less for y mph straight and level?

What if there's a wind? Is the straight train always more efficient compared to the circling one who's front or middle car is pointed the same direction (relative to the wind) as the straight train? Sagittarian Milky Way (talk) 17:48, 9 March 2022 (UTC)

Well, if it's a real train with real friction, in a curve I'd venture (pure wild assed guess) that more energy is used overcoming friction on the curves than on straightaway. --jpgordon^{𝄢𝄆𝄐𝄇} 19:48, 9 March 2022 (UTC)

That sounds right, how big of an effect is that though? Train wheels and rails are designed for low contact, only a small part of the tread width touching at any given time even in turns with sideways force and the flange not touching anything unless it makes that squealing subway turn sound. And for every curve of constant radius there should be a bank angle that balances speed y perfectly so there's no sideways force and I think no need to steer. I don't know if the gaps between train cars catch enough extra air in a turn to non-trivially affect air resistance. Sagittarian Milky Way (talk) 21:15, 9 March 2022 (UTC)

Oooh, check this out. A Survey of Wheel-Rail Friction. --jpgordon^{𝄢𝄆𝄐𝄇} 22:31, 9 March 2022 (UTC)

Looks interesting. Sagittarian Milky Way (talk) 23:01, 9 March 2022 (UTC)

Aside from friction, won't some energy in the circle train be wasted on acceleration that changes the direction but not the magnitude of the speed?--TZubiri (talk) 16:01, 10 March 2022 (UTC)

No. Assuming zero friction (from either air and rails), the kinetic energy of the train is conserved. Some force is necessary to change the direction, but that force is perpendicular to the direction of movement, and therefore produces no work.

For a simple demonstration of that fact, ride a bicycle on a flat surface (say an empty parking lot), cycle a bit to acquire some speed, then steer gently to the left or right. You can ride a full circle without exerting any force after you started steering, which would not be possible if doing a 90° turn ate all your speed. (The force that actually makes you turn is the reaction of the ground on the tires. Obviously, you will lose some speed because friction exists.) Tigraan^{Click here for my talk page ("private" contact)} 16:11, 10 March 2022 (UTC)