Wikipedia:Reference desk/Archives/Science/2015 November 15

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November 15

What is the differrence between foramen and canal (anatomy)?

I read about the foramens and canal of the skull bone and I don't understand what is the difference between them, here are both of them are holes, so what is the difference between canal (e.g. optic canal) and foramen (e.g. foramen rotundum)? 92.249.70.153 (talk) 04:10, 15 November 2015 (UTC)

A foramen is any sort of hole. The word "canal" carries the implication that the thing is relatively long in relation to its diameter. Looie496 (talk) 17:37, 15 November 2015 (UTC)

Not necessarily, but the distinction between a "hole" and a "passage" is what matters. A canal (anatomy) can be a single foramen (as in the optic canal, which is identical with the optic foramen), a longer structure with foramina at each end (as in the mandibular canal, terminated by the mental foramen and mandibular foramen), or pass through many different parts of the body (as in the spinal canal, which passes through each of the vertebral foramina). A foramen is one particular hole in one particular bone. Tevildo (talk) 18:31, 15 November 2015 (UTC)

The intervertebral foramina are holes formed between several adjacent bones that fit together. Looie496 (talk) 17:56, 16 November 2015 (UTC)

How thick of a layer of ice could every ship get through?

Including all time periods. Assuming moderate winds (quantity and quality). What kind of ship is most susceptible to having its progress stopped by ice? I can't find this easily, maybe because no one wants to be liable for a sinking but I couldn't even afford a boat much less a ship so this wouldn't be professional advice. Sagittarian Milky Way (talk) 11:21, 15 November 2015 (UTC)

The word "ship" is not all that well defined. From a coracle to the Titanic is a continuous progression, with no obvious splitting point. Looie496 (talk) 17:31, 15 November 2015 (UTC)

My father, who did a stint in the Navy, gave as the distinction that a ship carries boats (lifeboats and such). It's obviously not a perfect demarcation (presumably, a ship that loses all its boats in a storm is still a ship), but it might be a decent rule of thumb. --Trovatore (talk) 19:59, 15 November 2015 (UTC)

A line from Flip Wilson's version of Columbus' voyage: "Columbus cried, 'Lower the longboat!' - Which was really the short boat on the side of the big boat." ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:03, 15 November 2015 (UTC)

Not only what Looie said, but if you are talking about sea ice, it has to reach a threshold thickness, and this is often a result of winds or current. As stated, the question is too vague to answer. μηδείς (talk) 18:05, 15 November 2015 (UTC)

I would think a proper answer would require knowing how much force it takes to fracture ice at various thicknesses. The latest Old Farmer's Almanac has a list of thicknesses and how much weight they can tolerate - ranging from one person standing on it to a heavy truck driving on it. The data in that list don't address the OP's titled question here, but it's on a similar track. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:42, 15 November 2015 (UTC)

This has a formula for estimating the strength of lake ice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:58, 15 November 2015 (UTC)

Okay, clarifications: A ship is something big enough to carry it's own boat(s) (I've heard that one before, too). Sea ice says that it's new when thin and isn't solid ice until about 1 foot thick (there's a photo). So a solid layer of equal thickness like one a lake maybe might be harder than sea ice. Sagittarian Milky Way (talk) 20:41, 15 November 2015 (UTC)

You also have to consider the hull. A ship designed for speed might not have a hull strong enough to repeatedly break through ice, even if it has the power and weight to break it. Sjö (talk) 06:03, 16 November 2015 (UTC)

Including all time periods makes this a tough question. If we imagined something like (say) a Greek triereme - it's built for ramming, and therefore has an impressive bronze ram and a hull that's reinforced to survive forward impact very well - characteristics that might make it very good for breaking through modest amounts of ice...but because it's an oared vessel, once it has ice to either side, the oars would no longer be able to reach the water - and little progress could be made. Anything that relies on oars for propulsion is going to start getting into trouble long before it has to fracture the ice - simply because having lots of (say) two meter chunks floating past the hull would make rowing so difficult. In such circumstances, even if the ice were just inches thick, they might have a lot of difficulty in making headway. But whether this scenario is the absolute worst is hard to tell. Any kind of very wide - yet lightweight vessel is going to lack the momentum to break the ice on such a broad front - and such a ship might be even worse off than an oared galley. SteveBaker (talk) 00:53, 16 November 2015 (UTC)

Triremes did have sails (though they don't look very big). So they should still move without oars. And young ice might not have large chunks in it yet. Though if 1.1 inches thick was when a 180 pound man fell through in a test (referenced above) then that must still be a pain to row in unless weakened by waves or something. Sagittarian Milky Way (talk) 01:35, 16 November 2015 (UTC)

The Icebreaker article makes some interesting points which I've also seen from googling the subject. What the icebreaker does is fracture the ice and then basically plow through it. Ice does not bend very well, so even thick ice is relatively easy to get through once you have cracked it. However, icebreakers require machine power. No matter how strong a sailing ship's hull would have been, it would have been hard to keep going into only minimally fractured ice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:42, 16 November 2015 (UTC)

Gasoline powered electric car

Note, I'm not talking about hybrid cars or pure electric cars, as this is a very different concept. I was looking at, Integrated electric propulsion for submarines and such and wondered why was this never implemented for cars? It would eliminate the need for gearboxes, clutches, and thus having fewer moving parts making the car more reliable. So why not? ScienceApe (talk) 11:32, 15 November 2015 (UTC)

Yes, that's also how hybrid cars and diesel locomotives work, except that these marine units have two fuel-burning prime movers rather than just one. Such complexity pays off, in these far larger marine usages. Jim.henderson (talk) 11:37, 15 November 2015 (UTC)

IEP requires a prime source of power such as an internal combustion engine, a generator and at least one electric motor. In a large vehicle such as a ship, or a vehicle in which weight does not represent a significant penalty, such as a railway train, IEP provides an ideal means of propulsion. Conversely, in small vehicles like cars, and vehicles in which weight represents a significant penalty such as airplanes, the economics are very different; in these vehicles IEP does not provide an ideal means of propulsion - the economy of scale is against them. The efficiency of generators and electric motors increases with their size - if these pieces of electric equipment are to achieve high efficiency they have to generate and employ very large amounts of power. For small vehicles, the light weight and simplicity of a clutch and/or gearbox is superior to the combination of generator and electric motor. A friction clutch in a small vehicle is a very light-weight, simple and reliable element of a drive system. Once a friction clutch is fully engaged it transmits power with no losses; conversely, a generator and electric motor suffer I²R losses all the time and especially at high powers. Dolphin (t) 11:46, 15 November 2015 (UTC)

The GM Volt is, to within a whisker, an example of a series PHEV. The disadvantage for small cars is weight, because you have all the weight of a battery electric veicle, less some batteries, but plus an engine and a generator and a fuel tank etc. The series/parallel hybrid architecture, as used in a Prius, is lighter and often more efficient, as some of the power is transmitted mechanically. Various cars have been built as pure series hybrids, none are in production AFAIK. Greglocock (talk) 22:57, 15 November 2015 (UTC)

Check out the BMW i3.--Phil Holmes (talk) 08:47, 16 November 2015 (UTC)

The BMW i3 is interesting, but even with the optional gasoline-driven range extender engine it doesn't use integrated electric propulsion, which is what the OP was asking about. The gasoline range extender engine still requires a high-capacity (high-cost) battery system. Dolphin (t) 10:34, 16 November 2015 (UTC)