Tell us an interesting random fact you stumbled across

Your fingers wrinkle from being in water, not from water being absorbed, but from blood being *squeezed out from vasoconstriction.

*Not squeezed out into the water, but from the finger/toe tips back into the blood vessels.

I’ve got some experience with scales and balances. Most scales use a strain gauge-based transducer called a load cell. They’re basically a chunk of metal with some electrically resistive foil glued on the surface in certain spots. This resistance changes when the chunk of metal is loaded and bends since the foil bends with it. The resistors are arranged in a wheatstone bridge configuration which results in a variable voltage output in relation to the load. In this regard, a normal scale can be boiled down to a power supply to the bridge (usually between 5 & 15 VDC) and a voltmeter to measure the output (usually from 0 to 40 millivolts). There is much R&D put into how the metal chunk is machined or otherwise shaped so as to make the change in voltage linear (or proportional to the load), repeatable, with minimal hysteresis (it returns to zero when unloaded), and relatively immune to reasonable off center loading which may twist the load cell instead of bending it. Load cell scales are by far the most common and most people outside of laboratory or some industrial environments have never interacted with any other type. Scales on deli counters and grocery checkouts, digital kitchen or bathroom scales, scales to weigh trucks, baggage at the airport, overhead lifting like on cranes or even digital fishing scales all use load cells.

However, things don’t bend in straight lines, they bend in curves. Technology is always improving but beyond a figure that is constantly getting better, the change in voltage in response to changes in loads simply isn’t linear if you measure it at higher and higher resolutions. Right now, this is about 100,000 divisions, though some load cell scales can exceed this by a bit. After that, you need to use different technology and the most common is magnetic force restoration. In short, an electromagnet lifts the applied load through a series of levers & milled flexure surfaces and a control system measures the current to the magnet which is correlated with force of which weight is a particular type. A basic, nothing special commodity balance may be 220 gram capacity by 0.0001 grams resolution. This is 2.2 million individual divisions and probably gettable for under $1500. A really sensitive balance (link to 2.1 x 0.0000001 gram balance) might have nearly 10x more graduations. That one will set you back about $35k so try not to drop it. It can also measure a change of weight by simply taking it up or down a few flights of stairs or driving it a few miles away due to distance from the center of earth or changes in local gravity.

Calibrating against a known load is critical in some applications. It probably doesn’t matter for some freight or a 3lb bag of potatoes but might at the compounding pharmacy or aerospace development or materials development lab. Very good instruments will have internal calibration: there’s a mechanism inside the instrument that can lower a known-value weight onto a holder and it self-adjusts. This can help knock out those day-to-day errors that occur due to changes in temperature, humidity, and tiny changes in the level of the surface the balance is sitting on.

Heh, that weight is, please forgive me, a piece of crap. There are different classes of weights which are held to higher standards as needed. Here’s one that weighs 1 milligram and costs almost $600. Granted, it’s made of platinum but its aluminum equivalent is over $300. What other product can you put a half billion dollars worth of into a coffee mug and isn’t by virtue of it’s material value (like a super rare isotope or ultrahighend compound).

Obviously you don’t use $6 equipment from Amazon for your university physics research. It was only meant as an illustration of what I meant.

Great post! Very interesting, thanks.

On the last part: “Oh great, here’s my new $600 1mg calibration weight- ACHOO! Oh, shucks.” :slight_smile:.

Oh yes, load cells. I’d forgotten all about them despite the fact that my first job after University was with a company which made instrumentation for steelworks & used them quite a bit. Back in the day when the UK had more of a steel industry… bah, showing my age.

Wondering how one would use a 1 mg reference weight though? Seems as if some very delicate handling would be needed?

I thought it was called French Custard.

According to two sources, Elvis never played encores (this may be common knowledge, but I was 4 when he died, and I was unaware of this until now).

The origin of the famous phrase, “Elvis has left the building,” originally said to fans clamoring for more.

Since we are on the subject of balances…

  • When you measure the mass of something on a balance, the mass value it reports is not the real, actual, “inertial” mass of the specimen. This is true for even ultra-accurate analytical balances made by Mettler that can measure to a resolution of 0.01 mg. Instead it gives you the “conventional mass” value for the specimen. If you want to know the actual mass value for the specimen, you will need to know the air density in the room.

  • When you weigh a specimen using a balance, the balance assumes the density of the specimen is 8000 kg/m³. If the specimen does not have a density of 8000 kg/m³, there will be error in the reported value. (Note that even if the specimen has a 8000 kg/m³, the balance will still report the conventional mass value and not the actual mass value. See previous bullet for more info.)

Final note: the differences between actual mass and conventional mass are usually not significant for most things. So people don’t usually get too worked up over the fact that a balance reports conventional mass and not actual mass. But it’s good to always keep this in mind, since for some things it does matter. By the same token, the error due to the specimen not having a density of 8000 kg/m³ is usually not significant if the difference is not great. However, it could be significant if you’re weighing something that has very low density, e.g. dry paper.

[quote=“tofor, post:1223, topic:851674”]they have a
It was only meant as an illustration of what I meant.
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Yes, sorry, I didn’t mean to say you had bad tastes in weights, just that sky’s the limit when it comes to these things.

Darnel is a noxious weed that grows all over the world, especially where wheat is grown. It looks very similar to wheat and must not be harvested along with it because, when darnel is infected by a certain fungus, those who end up eating it get light-headed and nauseated and can even die if they eat enough of it. Darnel has been around forever and appears in literature from the Bible to Shakespeare (and in non-English lanugages, too) as a metaphor for a subversive force.

So the origin of the phrase “Elvis has left the building” was after Elvis left the building? Did you have some other expectation?

My post was a reply to the one immediately above about him never doing encores.

I wouldn’t go quite so far as to say that. Spring scales are still fairly common: Many folks have a spring scale for a postal scale or bathroom scale, if it’s older, and the produce section of a grocery store will often have spring scales hanging from the ceiling for approximate weighing of produce (though it’s still the load cell scale at the register that’s the official one). And while most folks don’t have a balance scale, it’s not uncommon to encounter one at a doctor’s office, and the two-pan balance still shows up in a lot of symbology (if that counts as an interaction).

So very sorry, that was an incredibly clueless stupid remark. I’m glad I don’t remember making that post, what ever whacked out reasoning underlay that thought must have been even stupider. :man_facepalming: :man_facepalming: :man_facepalming:

Here’s a twofer - the second part is much better than the first.

W E Johns, creator of the fictional ace pilot Biggles, lived in Lingfield, not far from us, for 10 years. This is where he lived, with the blue plaque* (which we spotted for the first time today) recording his period of residence. It made me look Johns up and…

… he was a First World War Flying Instructor, with an extraordinary record (per wikipedia):

On 1 April 1918, Johns was appointed flying instructor at Marske-by-the-Sea in Yorkshire. The aircraft of the time were very unreliable and he wrote off three planes in three days through engine failure – crashing into the sea, then the sand, and then through a fellow officer’s back door. Later, he was caught in fog over the [River] Tees, missed Hartlepool and narrowly escaped flying into a cliff. Shooting one’s own propeller off with a forward-mounted machine-gun with malfunctioning synchronisation was a fairly common accident, and it happened to Johns twice.

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(*) - Blue Plaques on buildings signify something of interest about them, frequently that a famous person lived there. Aside: the wiki article describes this one as “unofficial” - hmmm.

I already knew that, many years ago, universities and colleges used to supervise and monitor their students much more closely than today, both in their day-to-day lives and their coursework. For example, some type of P.E. was usually required. Opposite sex visitors in the dormitories were usually forbidden, and dorm residents might have to sign in and out, and be back at the dorm before curfew.

But what I didn’t know was that students often needed the dean’s permission to leave the town limits. USC and the U. of Oregon both had that rule once upon a time. If you were a student at USC, you needed the university’s permission to leave L.A.

How on earth would something like that be enforced?

The Dean kept the keys to your horse in his office.

That’s about how old these rules probably are. I attended USC in the 1970s. Any such rule would have died decades previously.

But for more on @Spectre_of_Pithecanthropus’ legitimate point see:

I know it too; and I also can’t figure out why. I seem to have it associated with school for some reason; but that might be wrong. – with skating?? was the thing played at ice skating rinks, which a school might have taken trips to? Or is my head just flailing around wildly trying to make some sort of connection?

(It’s certainly not the washington bridge thing, which I never heard of before.)