The Unit [Δαφνη Ευτυχια Αρθουρος]

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No, this isn't a sneaky relativity thing in honour of Einstein's birthday; just something that a random conversation got me wondering how other people think about. Assume v is a negligible faction of c if you're worried about that.

[Poll #946358] [Poll #946359]

I'm mostly just curious about the ways various people think about Units Of Stuff-ness ... though obviously I couldn't resist throwing in a wee dollop of goofiness.

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There are 23 comments on this entry. (Reply.)

It's a loosing fight as far as the general public goes, though. People in general simply aren't going to bother distinguishing between mass and weight.
Maybe if travel outside of a 1g field ever becomes widespread, but not until then.

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bingo. which is why i chose 'it does everywhere i'm likely to go'

BTW, glad to see you exist. Had tried to reach you the weekend.

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"Or even everywhere on earth."

Not only does the stuff I'm currently copyediting do a lot of explanations of newtons and the like, several of the books (it's a series, each state gets slightly different content, because they each have different standards and tests, plus some of the examples are tailored locally: Pennsylvania gets examples about its rivers, Louisiana about a train to New Orleans, etc.) have, as an example of reading data off a line graph, the acceleration of gravity at different latitudes.

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Uhm... seriously? How much of a difference IS there between latitudes?

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Not enough that you'd notice casually, but enough to be easily measurable. The polar radius of the Earth is about 20 miles greater than the equatorial diameter (since g=Gm₁m₂/d², reducing d increases g), and centrifugal force reduces felt gravity, again moreso at the equator and diminishing toward the poles.

A google on "gravity latitude" produces, among other things, links to calculators to let you take this into account when reading a barometer, and the information that the definition of g (i.e. Earth's gravity) specifies sea level at 45° latitude.

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If you're interested in the topic (and not just editing it), you may want to read the letter to Physics Today I mention below, in which a man experimentally verifies time dilation via altitude (he spent two days up Mount Rainier with his family, having installed cesium clocks both at home and in the minivan).

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FWIW: I know the definition of a slug but am horrible at estimation, so while I can calculate 1/6 of a slug of sugar, I can't visualize it very well. (Which is to say, I'm a geek. :)

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I guess I cheated, because in my head, a "slug" is defined as a measure of volume equal to the volume of an average-sized garden slug. So yes, I can visualize 1/6th slug of sugar.

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But to my reptilian mind, garden slugs aren't "average-sized", but rather, "tasty".

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*googles slug* Oh, cool, not encountered that. Newtons and more obscure scientific thingies, like the Kelvin temperature scale, are relegated to the part of the brain titled "Handy Scientific Knowledge, reference material". KNown but not utilised.

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lb<->kg is iffy because you're writing mass in pounds, not because you're writing weight in kg—even though you're using a scale to do it, the underlying question of interest is mass.

(I initially wrote "lb<->kb"; but of course that conversion would involve unreasonably large exponents.)

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lb/kb does vary a lot by year and media. Back in, oh, 1980, it'd have been a fairly valid measure of disk density...

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Efficiency of particular media is one thing; I am thinking in terms of the conversation rate intrinsic to the universe, which I would assume involves the Planck mass.

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Teach me to go years without touching a quantum textbook. I was thinking of a hypothetical "smallest nonzero rest mass", not the actual Planck mass.

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I can visualize a half-cup of sugar, and five pounds of sugar. One is what I dump in a quart of coffee, and the other is how I buy it.

A kilogram is a pound plus 10%, then doubled. A meter is a yard plus 10%. A kilosecond is 15 minutes plus 10%.

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Forgot my last line: and all of those depend on your local metric being equivalent to Earth sea-level normal.

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Hey, you've got me beat: I can visualize sugar only in the new matric measure known as the "packet." It's the thing I play with on the Diner tabletop while I drink my coffee black. :-P

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Needed to look up a slug to find its actual conversion; having done so, I can visualize it clearly.

On a tangential note, you might be interested in this: a man outfitted the family minivan as a superprecise mobile timekeeping station, synced it with similar gear at his home, then spent a couple of days atop Mount Rainier. When he came home, they found that, as predicted, they had experienced a time dilation of +22 nanoseconds.

The fact that I might some day travel to such an elevation (or even some significant differential from my current one) is the reason I didn't select the "likely to go" answer.

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I'll freely admit, I got confused due to an online conversation from years ago, and answered "slugs", despite that being the answer to kind of the opposite question :P By the time I realised that was wrong I'd already submitted, oh well.

In my defence, I've not been sleeping that well lately. And in my A-Level physics lessons, I don't believe imperial units were used even once, hence the revelation about pounds came as quite a shock when I had the aforementioned conversation years later :-O

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This got beaten into me in high school and college physics. The minute you said "weigh"...Anyway. As someone else points out, until excursions into non-1-g environments are common, folks won't use mass as a verb.

That being said, colloquially, it seems like people treat things weighing a pound in 1g as massing one 'pound', and pound as a unit of force is getting to be a more specialized usage. (Hunh: wikipedia agrees, emphatically. This must be in more common usage now than it was in said physics classes -- or wp got swamped by a "pound-force" advocate.)

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See, this is where I made my science teachers nuts... a kilo is a kilo is a kilo, no matter where you weigh it. How much stuff it takes to MAKE that kilo varies depending on location, but you still have to keep adding crap until it weighs a kilo, or it's not a kilo :)

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Yeah, but when your spring scale doesn't give the same answer as your balance scale, which measurement do you go by to determine when to stop adding crap?

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They never had enough sense to ask me that :)

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