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December 7, 2013 6:10 PM   Subscribe

The pressure of a human bite is about 1/9th of the atmospheric pressure on Venus. The fastest bacterium on earth is just outstripping the fastest glacier. A square meter of sunshine in the spring imparts about 1 horsepower.

Full list of Wikipedia's Order of Magnitude pages. Think you've got a pretty good handle on scale? Try your hand at some Fermi problems.

Obligatory xkcds.
posted by kagredon (20 comments total) 32 users marked this as a favorite

 
"Pressure exerted by a 45 kg woman wearing stiletto heels when a heel hits the floor."

Science!
posted by Navelgazer at 6:27 PM on December 7, 2013


Fun fact: early airplane designs did not account for women wearing heels and they would often punch holes through the floor.

One of the things I feel that modern engineering teaching does not stress is orders of magnitude applied to your answer. Great, you figured out your transmitter requires a thousand watts to operate, but what does that imply? Is that as much power as a lightbulb or a toaster or a server farm? What do similar transmitters use? How much in electricity is this going to cost? What kind of emissions are you looking at, given a certain power generation method?

A thousand watt transmitter is fine if it's a cell tower, but not if it's a smartphone.
posted by backseatpilot at 6:39 PM on December 7, 2013 [4 favorites]


This looks like a good place to promote my favorite personal project mymindblewup.com.

You can generate comparisons for the number of cows required to cover the distance from the Earth to the Moon, see a large table of all number names, or find out how deep we'd be in pirates if 1,000,000 rained down onto the Earth.
posted by HappyEngineer at 6:42 PM on December 7, 2013 [6 favorites]


This is damn cool. That is all.
posted by Canageek at 6:47 PM on December 7, 2013


A square mile of sunshine in the spring imparts about 1 horsepower.

This one didn't pass the smell test for me (seemed way too low), and according to the linked Wikipedia page, it is in fact one square meter, which is quite different from a square mile, in that a square mile is ~2.6 million square meters.

So that means that a square mile of sunshine in the spring in fact imparts about 2.6 million horsepower.
posted by jcreigh at 6:50 PM on December 7, 2013 [18 favorites]


Oh geez, good catch jcreigh. Meter! Not mile.
posted by kagredon at 6:56 PM on December 7, 2013


Ahh. Thank you on that meter/mile thing. I thought the sun was more powerful than the hp-per-square-mile figure too.
posted by Wild_Eep at 7:11 PM on December 7, 2013


i thought you would, Wild_eep.

me too, of course. i also knew this.
posted by a birds at 8:07 PM on December 7, 2013


A square mile of spring sunlight does exert about 10N of radiation pressure radially outwards from the sun, however. Earth's orbit has an eccentricity of about 5 gigameters, and a period of 30 megaseconds, so average radial velocity is 300 meters per second. P=Fv=10N * 333m/s = 3kW or about 4 horsepower :)
posted by memetoclast at 8:15 PM on December 7, 2013 [2 favorites]


Fun fact: 25! (i.e. "25 factorial", for those of you who didn't study mathematics) is the first factorial where the magnitude of the result is greater than the argument. I.e. 25! is larger than 1025, and it's the first factorial where x! is larger than than 10x.

Don't know why I mentioned that, but y'all are talking about large numbers, and I don't have any fun large number physics trivia to contribute, but a math teacher once told me that you should remember that 10! is roughly 3.5 million, and that 25! is more than 1025. Remember that and you'll have the basic scale of the first couple of factorials down.
posted by gkhan at 8:40 PM on December 7, 2013 [4 favorites]


What about some really fun conversions? I want to know what size meteor strike is equivalent to the cumulative impact of every step I will take in my life.
posted by George_Spiggott at 9:44 PM on December 7, 2013 [3 favorites]


The Fermi problems are kind of fun, but a lot of them assume you're American, or familiar with University of Maryland-specific things, like the cost of full tuition there, or how many students there are.
posted by Joakim Ziegler at 10:57 PM on December 7, 2013


[Fixed the mile/meter problem in the post for those who may not read the comments.]
posted by taz at 11:54 PM on December 7, 2013


Here's one relating to computing power. Moore's "Law" stating that computing power doubles every 18 months (1.5 years) corresponds to factor of 10 every five years (2^(5/1.5) is about 10). This is a factor of 100 every ten years, a factor of 1,000 every fifteen years, and a factor of 10,000 every twenty years.

Since there are about ten thousand hours in a year, what took a year to compute in 1993 would take about one hour to compute in 2013.

Now imagine that one had a computational problem in 1993 that would take twenty-five years to compute on a state of the art desk top computer of the day. One would have been better off waiting twenty years to buy a computer and then running the problem overnight to finish five years early. Or even better one could have waited fifteen years and run the problem for about 1.5 weeks to finish about ten years early.

This begs the question: how long should one have waited to start the problem to finish the computation the soonest? The solution is left as an exercise for the reader.
posted by haiku warrior at 8:08 AM on December 8, 2013 [9 favorites]


This begs the question: how long should one have waited to start the problem to finish the computation the soonest?

Well, if my undergrad taught me anything, it's that you should wait until the night before it's due.
posted by jcreigh at 8:55 AM on December 8, 2013 [3 favorites]


A classic video on Orders of Magnitude, from Charles and Ray Eames:
http://www.youtube.com/watch?v=0fKBhvDjuy0
posted by alacrity at 9:47 AM on December 8, 2013


Was talking on Facebook recently about a naked mole rat, and decided that a mole of naked rats could cover the U.S. 12km deep in shaved rodents.
posted by Monkey0nCrack at 10:52 AM on December 8, 2013


Speaking of which, xkcd What If did one on a mole of moles early on.
posted by Punkey at 11:55 AM on December 8, 2013


A sheet of white paper in sunlight emits as much light as a 100w bulb.
posted by CaseyB at 7:59 AM on December 9, 2013


haiku warrior: "This begs the question: how long should one have waited to start the problem to finish the computation the soonest? The solution is left as an exercise for the reader."

The idea of "later to start, sooner to finish" shows up in the classic A.E. van Vogt short story, "Far Centaurus."
posted by Chrysostom at 12:26 PM on December 9, 2013


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