[QUOTE=Nick;426307]It's good to see people get enthusiastic about "cool" mathematics but frustrating that if only they knew just a little more then far more cool stuff would come within their field of perception!

Here is a recent public lecture Prof. Martin Bridson gave for non-mathematicians on group theory and geometry.

(Warning: this is a 1Gbyte mp4 file downloading from Oxford in the U.K.)
[URL]https://media.podcasts.ox.ac.uk/maths/oxford-maths/2015-11-25_maths_bridson.mp4[/URL][/QUOTE]
Not sure if this counts as a math fact, but I find it to be the coolest "math fact" I know:

If you put a mirror to the right or left of 3.14(written in this particular font), you get the word PIE.

If that doesn't count, then I recruit the shortcut methods used to figure out of small numbers are a factor of larger numbers:

Even numbers are all divisible by 2, if the digits of a number add up to a number divisible by 3 the number itself is divisible by 3, if a number ends in 0 or 5 it is divisible by 5. Unfortunately, I don't know the rule for 7. And then, of course, you can combine them. If the rule for 2 passes, and also the rule for 3, then the number is divisible by 6.

[QUOTE=jasong;426696]Even numbers are all divisible by 2, if the digits of a number add up to a number divisible by 3 the number itself is divisible by 3, if a number ends in 0 or 5 it is divisible by 5. Unfortunately, I don't know the rule for 7. And then, of course, you can combine them. If the rule for 2 passes, and also the rule for 3, then the number is divisible by 6.[/QUOTE]Note that these procedures are not universal. The ones you mention work for base-10 (decimal). Other bases may require different procedures.

[QUOTE=Uncwilly;426486]3 issues with this article:
Is the weight of the jets distributed over 1 cm[SUP]2[/SUP] or 10 football pitches?

The author talks about the density of the ice, but never give an actual number.

There is no link to the original paper or any more robust source.[/QUOTE]
My answer to that is to ask them how many jumbo jets a normal person shoulders. Then, you can figure out what they're talking about.

But, yeah, I lot of science articles aren't actually all that scientific.

[QUOTE=retina;426697]Note that these procedures are not universal. The ones you mention work for base-10 (decimal). Other bases may require different procedures.[/QUOTE]
Very true.

In binary, fast fourier transforms would be the most interesting thing. In base-6, it would be the fact that all primes other than the first 2 are 1 more or 1 less than the base.

Another interesting thing I just thought of is googlin the explanation of why clocks and anything involving circles involves things like base-12.

You can also apply the +/- criteria for divisibility by 11.
Since I was very small I "invented" (yes, by myself!) a criteria to test very fast the divisibility by 7, 11, and 13 in the same time, based on the fact that their product is 1001. When I showed it to my teacher in grade 8, she looked to me like I was some alien, or strange animal... (she was a very kind lady, and a gorgeous woman, single mom, not really qualified for math, just "making a living", in that small town I grown up, one "distraction" our [STRIKE](idiots)[/STRIKE] colleagues had at that time was to put a small mirror in between the strings of their shoes, so they could look under her skirt...).
A similar criteria can be devised to test for all primes including 17, considering that their product is 510510 (or, 255255 if you leave 2 out), but that is not so simple, it need 2 more operations :wink:.

[QUOTE=LaurV;426777]When I showed it to my teacher in grade 8, she looked to me like I was some alien, or strange animal...[/QUOTE]
That is reminiscent, if not as drastic in its consequences, of the recent incident when a boy in Texas brought a home-made clock to school to show his teacher.
[URL]https://en.wikipedia.org/wiki/Ahmed_Mohamed_clock_incident[/URL]

[url=www.bbc.com/news/election-us-2016-35609636]US election: Donald Trump v Pope... who wins?[/url] - BBC News

Re. Donzilla v. Pope-thra -- will this rather amusing public spat lead to a KO strategy called the "Pope-a-Dope"? Inquiring minds want to know. A pro-wrasslin-style blustery calling-each-other-out would also be a nice touch. "Ahm comin' to gitcha, Frankie baby ... ahm gonna knock that fancy-pants miter off yer head and chase ya back to Vatican City with it!" Francis for his part, being a Latino wrassler, would of course be wearing a Lucha Libre mask - he could do it up with a big red X like boxer Bernard "The Executioner" Hopkins, and adopt the ring nick "The Excommunicator". I'd pay a generous PPV tithe to watch that.

[url]https://reddit.com/r/badmathematics[/url]

[QUOTE=ixfd64;428537][url]https://reddit.com/r/badmathematics[/url][/QUOTE]
here's one that brothers me:
[url]http://www.google.com/search?q=temperature+precipitation+lunar+weight+atmosphere[/url]

In low order effects they've noticed higher precipitation in the atmospheric tidal bulge, which they attribute to higher temperatures caused by additional atmospheric [I]weight[/I] causing pressure in the bulging region.

I don't think that the extra atmospheric mass of the bulge weighs more in a Boyle meaningful way while the moon is pulling on the other end. For this small effect, it could be a longer precipitation column or sound travel time or even a difference in light propagation or scattering or a dust column or a gazillion other miniscule influences.

[QUOTE=only_human;428570]here's one that brothers me:
[URL]http://www.google.com/search?q=temperature+precipitation+lunar+weight+atmosphere[/URL]

In low order effects they've noticed higher precipitation in the atmospheric tidal bulge, which they attribute to higher temperatures caused by additional atmospheric [I]weight[/I] causing pressure in the bulging region.

I don't think that the extra atmosphere of the bulge weighs more in a Boyle meaningful way while the moon is pulling on the other end. For this small effect, it could be a longer precipitation column or sound travel time or even a difference in light propagation or scattering or a dust column or a gazillion other miniscule influences.[/QUOTE]
From a side box:
[QUOTE]Another UW [URL="http://www.washington.edu/news/2015/04/27/tidal-tugs-on-teflon-faults-drive-slow-slipping-earthquakes/"]study[/URL] last spring showed that the tug of the moon nudges tectonic faults in the Earth’s crust.[/QUOTE]
The Earth's tidal forces on the Moon must cause tremors there. It seems the stresses would be a lot greater. However, I guess that without tectonic activity, there would be fewer faults to disturb.

[QUOTE=kladner;428573]From a side box:

The Earth's tidal forces on the Moon must cause tremors there. It seems the stresses would be a lot greater. However, I guess that without tectonic activity, there would be fewer faults to disturb.[/QUOTE]
That could also be relevant to the precipitation: piezoelectric effects; or maybe friction as the bulge follows the moon.