Wikipedia:Reference desk/Archives/Science/2016 April 15

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April 15

How closely do compression coil springs obey Hooke's law?

The spring article says:

   When a coil spring is compressed or stretched slightly from rest, the force it exerts is approximately proportional to its change in length (this approximation breaks down for larger deflections). 

According to Hooke's law, a coil spring compressed to 50% of its uncompressed length exerts 5 times the force compared to the same spring compressed to 90% of its uncompressed length. But this relationship breaks down when the spring is compressed to its extremes. I'm trying to figure out where exactly this "extreme" region starts.

1. Does the relationship still hold when the spring is compressed to 25% of its uncompressed length? What about 20%?

2. The real-life behavior of springs obviously differs from a first-order linear approximation like Hooke's law, but is the actual force higher or lower than predicted? For example Hooke's law predicts that a coil spring compressed to 10% of its uncompressed length exerts 9 times the force compared to the same spring compressed to 90% of its uncompressed length. Is the actual force lower or higher in the real-world case? Johnson&Johnson&Son (talk) 05:29, 15 April 2016 (UTC)

Real coil springs expand in width slightly as they compress, thereby reducing their spring rate. it is fairly easy to work this effect out, lazy physics professors don't bother, real life spring engineers do. Big clue, the length of the wire stays the same. Greglocock (talk) 07:10, 15 April 2016 (UTC)

How much would it cost to make diamond food and drink vessels?

I read that diamond can be manufactured instead of just mined. How much would it cost to make bowls, glasses, plates etc from diamond? They would be resistant to accidental breakage. — Preceding unsigned comment added by 78.148.105.117 (talk) 08:02, 15 April 2016 (UTC)

Diamond is hard but it still shatters. I've dropped and shattered plenty of glass bowls and glasses in my life time, and had they all been made of diamond instead, at least half of them still would have shattered. On the other hand, they would have all survived had they been stainless steel or some other similar material. Johnson&Johnson&Son (talk) 08:14, 15 April 2016 (UTC)

Currently, manufactured gem-quality diamonds are priced at about 50-80% of their mined counterparts. Part of that is so the manufacturers can make a tidy profit, but it is also the case that manufacturing diamonds is still rather expensive. We can make cheap diamond powders for industrial uses, but creating a solid diamond the size of a bowl or a glass is going to be wildly expensive. Dragons flight (talk) 09:10, 15 April 2016 (UTC)

People forget that hardness and strength are not quite the same. Hardness can be viewed as an "aspect" of strength, but it is only one aspect. Diamond is not especially strong by most measures. — Preceding unsigned comment added by Star trooper man (talk • contribs) 12:11, 15 April 2016 (UTC)

Specifically, Diamond is tops in (AFAIK) only one important measure of strength, Scratch hardness as commonly measured on the Mohs scale of mineral hardness. Words like "hardness" and "strength" are very imprecise, and one needs to clarify the EXACT property one is measuring. In the case of diamonds, what is being looked at when one calls diamonds hard is scratch hardness. On other measures of "strength" diamond is not always particularly strong. --Jayron32 12:15, 15 April 2016 (UTC)

Not only is hardness not the same as toughness, it is often the opposite, because hard crystals have no "give", so any impact is concentrated right at the point of impact, rather than spread out over a wider area, as happens with tougher materials, like steel. The diamond industry perpetuates the myth that diamonds are indestructible, with lines like "Diamonds are forever", but they are actually fairly fragile. It's only hard to damage them because they are tiny, and mounted on gold rings, which can absorb some impact, on a finger, which can absorb even more impact. Cut glass would also be difficult to damage like that. On the other hand, if you had windows made out of large sheets of diamond, they would break quite often. StuRat (talk) 17:40, 15 April 2016 (UTC)

Apart from mechanical fragility, I have read somewhere that they also burn quite readily, but I'm having trouble finding an explicit reference. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 18:25, 15 April 2016 (UTC)

Well, readily perhaps, in that once you start it, it keeps burning on its own. But I wouldn't say it burns easily. About 900º C ignition temperature for diamond, compared to 300º C for wood, according to this [1] (Magnesium is ignited at 473 °C for a reference to something non-wood that many us have ignited). Here's some gritty details on empirically derived heat of combustion for diamond [2], in case anyone is interested. SemanticMantis (talk) 18:41, 15 April 2016 (UTC)

Rather than diamond, conventional glass and ceramics will better fit the bill. CorningWare and Pyrex are two brands of cookware resistant to thermal shattering. I believe there are also version resistant to breakage from dropping. StuRat (talk) 18:52, 15 April 2016 (UTC)

This very argument was played out when Apple were thinking of releasing an iPhone with a sapphire glass screen but went for gorilla glass instead. Yes the sapphire resists scratches better - but needs to be cut thinly and laminated with a tougher base to stand up to being dropped. It is used for watches. Dmcq (talk) 16:58, 17 April 2016 (UTC)

Number of coils in a torsion spring and its torque

For a compression spring of a given length, wire diameter, and outer diameter, the higher the number of coils the higher the spring constant. In fact, if I'm not mistaken there's a linear relationship between the number of coils and the spring constant. This is pretty intuitive, the more “stuff” you have, the “stronger" it gets.

I'm having a major brain fart here, but it seems to me that for a torsion spring, the relationship is in the opposite direction. If you double the number of coils of a torsion spring, (it seems to me that) its spring constant would actually decrease. Is this actually true? The more “stuff” you have, the “weaker" it gets when it comes to torsion springs?

I apologize if this is obvious. Like I said I'm having a brain fart here. I checked McMaster-Carr to find example of torsion springs that have the same wire diameter but different number of turns but couldn't find any. Johnson&Johnson&Son (talk) 10:39, 15 April 2016 (UTC)

I think you're right, according to the formula on this [3] page for "torsion spring rate" (K) of a torsion spring. They give an expression $K={\frac {otherterms}{constant\cdot D\cdot N}}\;$, where N is the number of turns, and D is the mean coil diameter. Other terms come in to play to of course, but that highlights that in the limit $N\to \infty$, the spring tends toward infinite turns and zero resistance to turning. SemanticMantis (talk) 16:01, 15 April 2016 (UTC)

"the higher the number of coils the higher the spring constant" No. rate is inversely proportional to N. Greglocock (talk) 22:24, 15 April 2016 (UTC)

Thermally stable and polymerisation inert agents for OMCR

What kind of organic coolants (and moderating agents) have better thermal stability and inertia to polymerisation perform better than polyphenils in Organically moderated and cooled reactors?--5.2.200.163 (talk) 14:40, 15 April 2016 (UTC)

Are some compounds based on organosilicon a good option?--5.2.200.163 (talk) 14:42, 15 April 2016 (UTC)

Biomedical engineer

Where do biomedical engineers mainly work? In offices? 2A02:C7D:B907:6D00:5C:AFF:B16F:6BCE (talk) 20:12, 15 April 2016 (UTC)

Wikipedia has an article titled Biomedical engineering. You can read that and arrive at your own conclusions. If you want to know what professional biomedical engineers do, the best option is to find a university that has a program in biomedical engineering, contact them, and ask them. --Jayron32 20:18, 15 April 2016 (UTC)

Engineering work has become very project-fucused during the last 20 years and thus Engineers are hired and fired at high frequency today. Especially when starting fresh chances are very high you will work for specialized Temp agencies. --Kharon (talk) 11:18, 16 April 2016 (UTC)

Umm, complete nonsense. Companies like Medtronic and others hire engineers just like Intel Corporation. --DHeyward (talk) 07:47, 17 April 2016 (UTC)

My Dad was a biomed engineer, and he worked in a hospital; testing, repairing, and occasionally modifying equipment, as needed. StuRat (talk) 05:10, 17 April 2016 (UTC)

Did he spend most of his days at a desk or staring at a screen? Is it also quite repetitive? 2A02:C7D:B907:6D00:B0EE:31D9:DB3D:39DA (talk) 16:44, 18 April 2016 (UTC)

No, he would go to the various rooms in the hospital to service equipment in each room, where possible, and remove it for maintenance in the shop, where not. He did use an oscilloscope to test some equipment, and used a digital multimeter quite often. Some soldering was involved (for some reason many of the batteries for those devices are soldered into place, maybe that makes them more reliable, since they weren't as likely to jiggle out of contact ?). StuRat (talk) 22:43, 18 April 2016 (UTC)

Engineering has always been project focused. Designing something for a specific requirement is a project. Otherwise we'd just be designing random things with no purpose. 2A02:C7D:B907:6D00:D185:96E9:64E3:36EB (talk) 21:57, 17 April 2016 (UTC)

Geyser (water heater)

Can one still get geysers to heat your water in the UK? In my experience they were extremely reliable, produced copious hot water as fast as you wanted it, and didn't switch themselves off in a power cut like modern gas boilers do. DuncanHill (talk) 20:31, 15 April 2016 (UTC)

Do you mean like this or these? Richerman (talk) 21:12, 15 April 2016 (UTC)

No, a geyser is gas-fired, not electric (if it was electric, it wouldn't work in a power cut. Modern gas boilers incorporate electric timers and the like, hence their uselessness when the electric's off). DuncanHill (talk) 21:20, 15 April 2016 (UTC)

Oops- sorry - of course it would (blush!!) - we always used to call those Burco electric boilers a "geyser" (clearly erroneously). Looks like there was an LPG gas heater that used battery ignition [4]but it's not presently available. Richerman (talk) 22:16, 15 April 2016 (UTC)

My impression is that they were outlawed in the UK (more accurately they now have to be installed external to the building). I've just bought one from China for my off grid weekender. It uses 2 D cells to operate the igniter rather than having a pilot. $200. My house has a somewhat larger device which is used to top up my solar heated hot water, it is pretty much the same device, but designed for permanent installation and uses mains power to run the electrical side. $800. https://www.immerge.com.au//immerge-hot-water-systems-melbourne/products/continuous-flow-hot-water-systems/rinnai-infinty-26-touch-detail?gclid=CMnK-7LWkcwCFYiCvQodXp8Hmg Greglocock (talk) 22:22, 15 April 2016 (UTC)

Here in the US, where safety isn't as much of a concern, apparently, gas water heaters with pilot lights are not only allowed inside the house, they are quite common. StuRat (talk)

You could power the boiler via a uninterruptible power supply if you want it work during brief (several hours) electricity failures. LongHairedFop (talk) 10:04, 16 April 2016 (UTC)

Think DuncanHill is referring to the once ubiquitous Ascot geyser. They were OK when homes where very draughty and well ventilated, ensuring that any CO didn’t build up too high. By the 1970's however, they where causing too many deaths. So now a fan has to be integrally fitted and one is recommended to have the appliance checkout at regular intervals by a qualified geyser. Even externally mounted ones now have fans (increases efficiency), and being external that needs electrically powered frost protection to. I think I know what DuncanHill's desire comes from. They where small, fairly cheap, easy to fit and gave instant hot water. But it is only the old geysers that can remember them now ;-) --Aspro (talk) 15:02, 17 April 2016 (UTC)

If power outages are common why not get a portable generator like the ones shown here. You can do a bit more with one than just heat water. Leave it running outside and run extension cords inside. You can run a few lights, a hot plate to cook, an electric heater, coffee pot and even run the TV and DVD/HDD with all your films on. My son-in-law brings his to town from their cabin in the fall and use it when the power is out. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 15:37, 17 April 2016 (UTC)

I live in a one-bedroom flat with no garden. I'm not running a genny in my living room, and I doubt the council would let me keep one in the street! DuncanHill (talk) 14:51, 18 April 2016 (UTC)

Think you miss DuncanHill's drift. Brownout's and cuts are very uncommon in the UK. He was just making an aside that a further advantage was that Ascot's did not need electricity.--Aspro (talk) 12:28, 18 April 2016 (UTC)

To enlarge on the advantages, in the UK heating water with gas is markedly cheaper than using electricity; heating the water only on demand is markedly cheaper than keeping an immersion heater tank permanently hot (particularly for single-person households), and having a gas-powered hot water supply separate from one's electric supply and one's gas central heating means that if either fail, hot water is still available.

Contrary to Greglocock and Aspro, such internally mounted (though externally vented via balanced flues) gas water heaters are in the UK still both legal and available from several manufacturers (though not the defunct Ascot). {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 13:35, 18 April 2016 (UTC)

Quite so, with regard to the advantages. DuncanHill (talk) 14:51, 18 April 2016 (UTC)

Well do tell who supplies them then, because this is what the OP wants to know. I know there are some for mobile food stalls etc (ie open to the fresh air)., but I haven't come across a modern one for domestic use yet.--Aspro (talk) 14:37, 18 April 2016 (UTC)

The shorty answer to "Can one still get geysers to heat your water in the UK?" is yes. Some examples with and without exhaust (using batteries for the electronics): [5], [6], [7].
Even a dolly for on the road [8].--TMCk (talk) 15:45, 18 April 2016 (UTC)

• Found a reference regarding direct gas to hot water in mobile catering trailers and the like with no 'trity involed and it states:

Modelling using the BREEZE program showed that the concentration levels set for the HSE Short-Term Exposure Limits for CO2 and carbon monoxide (CO) will rarely be exceeded within typical UK dwellings. However, those for the HSE eight-hour OES for CO2, and the WHO guideline concentrations for CO are much more likely to be exceeded in situations where there is prolonged use of a flueless appliance.[9]

With a few million households using Ascots, a few fatalities where to be expected. From memory they tended to be OK in the kitcken because before frozen food and microwave ovens, vegtables had to be boiled for some 20 minutes and so a window had to be open to ovoid too much condensation. In the bathroom however, people kept their windows closed and relaxed and fell asleep in into a nice hot tub that they didn't wake up from. Now days in the UK we can't even have mains sockets in the bathroom in case someone decides to dry their hair with a hair-drier whilst sitting in the bath.Aslo, in the availability examples given above: [8] is for LPG not NSG. [9] needs 'tricity for the fan and LPG not NSG [10] LPG not NSG. Therefore, non are suitable as a simple substitute for the good old Ascot which the OP hungers for.--Aspro (talk) 16:30, 18 April 2016 (UTC)

States of matter/transfer of energy

Transferring energy through fluid pressure = hydraulics Transferring energy through gas pressure = pneumatics Transferring energy through solid(s) (pressure?) = mechanics? or mechanical systems? (I just thought of this and would like some input on the validity of this statement like planetary gears on a mechanical differential or a torque wrench etc) What about plasma!?!? If such technology does not exist, has anyone tried to research/invent this? Is it possible/practical? 199.19.248.20 (talk) 23:57, 15 April 2016 (UTC)

Transferring mechanical energy through solid mechanics is broken down into several types, such as compression, torsion, bending, collisions, etc. StuRat (talk) 00:05, 16 April 2016 (UTC)