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 [quote="Doc Borodog"]I always teach my kids to take square roots and logarithms of large numbers in their heads, and then tell them to amaze their friends at parties. To approximate the square root of a number, use the root of next lowest perfect square plus the difference between the number and the perfect square divided by twice the perfect root. For example, the square root of 85 is 9 (85-81)/(2x9) = 9 4/18, or 9 2/9, or 9.22. To take base 10 logarithms in your head, just remember the numbers 0, .3, .5, .6, .7, .8, .85, .9, .95, and 1. These are the base 10 logarithms of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10, respectively (or near enough). To take the logarithm of any large number, think of it in scientific notation, like 70 trillion is 7x10^13. Since log(7x10^13) = log(10^13) + log(7) = 13 + log(7) = 13.85. In other words, the whole number is the exponent and you just add the logarithm of the coefficient, which you've memorized from the list. People seem really impressed when you can tell them the logarithm of 40,000 is 4.6, or tell them the square root of 68 is 8.25, without using a calculator.[/quote]
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MTGAP
Posted: Mon Aug 04, 2008 2:55 am    Post subject: 1

Antares is very big. How big is that compared to the solar system? Like, would it be bigger than Earth's orbit around the sun?
MTGAP
Posted: Mon Aug 04, 2008 2:52 am    Post subject: 0

rolandofthewhite wrote:
Our psychology teacher made us watch a movie about bonobos. It was basically one giant monkey porn.

Once in science class we spent the whole day talking about how different animals have sex. I think dolphins are the most interesting. Dolphins not only pleasure themselves, they have flexible penises and ejaculate after about 12 seconds. (Don't worry–they get multiple ejaculations.)

It's interesting how only relatively intelligent life pleasure themselves. You'd think the intellectuals would do more thinking and less !@#\$ing*. But instead, it's just the opposite. Maybe other species aren't clever enough to think of having oral sex.

I feel bad posting three times in a row (and possibly more), but that's what comes from having a really inactive thread.

*that word fit, but I can't bring myself to say it
MTGAP
Posted: Mon Aug 04, 2008 2:44 am    Post subject: -1

L'lanmal wrote:

That's really interesting. I live in the red area and call it soda, and anything else seems really weird to me.
MTGAP
Posted: Sun Aug 03, 2008 8:23 pm    Post subject: -2

Courk wrote:
The fifth sense of taste (I can't think of the right word) is umame. It's described as savory.

It's described as what MSG tastes like. Salty is salt, sweet is glucose, bitter is bases, and sour is acids. (Salt is what you get when you mix acids and bases.)

On the topic of senses, people actually have 9 senses, not 5, and arguably have more. Those 9 are smell (chemical reception), sight (electromagnetic wave perception), hearing (sound perception), taste (chemical perception), touch (pressure perception), pain perception, temperature perception, balance perception, and positional perception (where each part of your body is relative to each other part). Possibly categorizable as senses are sense of acceleration and sense of time.
Jack_Ian
Posted: Fri Jan 11, 2008 3:20 pm    Post subject: -3

The American civil War in 4 minutes

Coke machine Jackpot (I'd love to know if this actually works)
Jack_Ian
Posted: Tue Jan 08, 2008 6:17 pm    Post subject: -4

Jack_Ian wrote:
Courk wrote:
How much would be "most of the sky"? 99% or more? That's what I'm picturing, and I have no idea if that's right.
Our Sun is 32 arc minutes across when viewed from Earth. (i.e. 32/60 degrees)
Antares is approximately 700 times the diameter of our sun.
Distance to Sun is 149 597 870 691 meters (± 30)
Diameter of our sun is 1392000000 meters
The sun is therefore approximately 107 Sun Diameters from Earth.

The formula for calculating the relative size of Antares in the sky is given by:
Tan -1 (700/(2 x 107)) = 73 degrees = approximately 0.4 of the sky.

So not most of the sky after all, in fact not even half.

So, is this 73*60/32 = 136.9 times larger than the sun in the sky?

I forgot to take the radius of the star into account.

The correct value should be:
Tan -1 (350/(107 + 350)) = 37.45 degrees

The surface of the star is the same distance away as the edge of our sun but the same can not be said for their centers.

So that makes it (37.45 x 60)/32 = 70 times larger in the sky.
Posted: Tue Jan 08, 2008 5:47 pm    Post subject: -5

Jack_Ian wrote:
Courk wrote:
How much would be "most of the sky"? 99% or more? That's what I'm picturing, and I have no idea if that's right.
Our Sun is 32 arc minutes across when viewed from Earth. (i.e. 32/60 degrees)
Antares is approximately 700 times the diameter of our sun.
Distance to Sun is 149 597 870 691 meters (± 30)
Diameter of our sun is 1392000000 meters
The sun is therefore approximately 107 Sun Diameters from Earth.

The formula for calculating the relative size of Antares in the sky is given by:
Tan -1 (700/(2 x 107)) = 73 degrees = approximately 0.4 of the sky.

So not most of the sky after all, in fact not even half.

So, is this 73*60/32 = 136.9 times larger than the sun in the sky?
extro...*
Posted: Tue Jan 08, 2008 5:17 pm    Post subject: -6

I've always liked those pics, but from looking at them I've always thought they're really poor quality reproductions (grainy, jpeg artifacts) of some really nice computer graphic originals. Have never been able to find the originals though.
Jack_Ian
Posted: Mon Jan 07, 2008 8:25 pm    Post subject: -7

Courk wrote:
How much would be "most of the sky"? 99% or more? That's what I'm picturing, and I have no idea if that's right.
Our Sun is 32 arc minutes across when viewed from Earth. (i.e. 32/60 degrees)
Antares is approximately 700 times the diameter of our sun.
Distance to Sun is 149 597 870 691 meters (± 30)
Diameter of our sun is 1392000000 meters
The sun is therefore approximately 107 Sun Diameters from Earth.

The formula for calculating the relative size of Antares in the sky is given by:
Tan -1 (700/(2 x 107)) = 73 degrees = approximately 0.4 of the sky.

So not most of the sky after all, in fact not even half.

(Edit: Made a mistake. Correct value 37.45 degrees. See post231)
Courk
Posted: Mon Jan 07, 2008 6:33 pm    Post subject: -8

Hey, the Sun, Pollux, Arcturus, Betelgeuse, Aldebaran, and Antares are all the same ball!

How much would be "most of the sky"? 99% or more? That's what I'm picturing, and I have no idea if that's right.
Jack_Ian
Posted: Mon Jan 07, 2008 5:53 pm    Post subject: -9

I'd guess black. No atmosphere. (apart from the Sun, which would take up most of the sky during daytime)
The rest of Earth would be black too (once it cools down).
Courk
Posted: Mon Jan 07, 2008 4:35 pm    Post subject: -10

If Earth orbited Antares at the same distance from the surface it orbited the Sun, what would that look like in the sky?
Jack_Ian
Posted: Mon Jan 07, 2008 12:17 pm    Post subject: -11

Antares is the 15th brightest star in the sky. It is more than 1000 light years away.
Antrax
Posted: Mon May 22, 2006 11:49 am    Post subject: -12

extro: Kudos. I couldn't find a way to put Rice's theorem into simple words
extro...*
Posted: Mon May 22, 2006 11:37 am    Post subject: -13

Antrax wrote:
It is impossible to write a computer algorithm that receives another computer program and input values to it, and correctly tells you if the program will run forever or not. Assuming such an algorithm exists creates a logical contradiction.

A much more general result, which can easily be used to prove the above, and a whole lot more, is Rice's Theorem:

Write any computer program, P, which takes another computer program as input, and returns true or false. Then, either:
a) P always returns true.
b) P always returns false.
c) P will return true for one input program, and false for another, for some pair of programs which compute the same function (i.e. produce the same output whenever given the same input).

What that means, basically, is that if you have in mind some property of functions, you can't write a program that determines if another program computes a function with that property (unless the poperty is "trivial" - true for all functions, or false for all functions). It will sometimes say yes, and sometimes say no, for two programs that compute the same function.
Posted: Mon May 22, 2006 8:43 am    Post subject: -14

The "halting problem." Read that in my discrete math book, pretty cool.
Antrax
Posted: Mon May 22, 2006 8:26 am    Post subject: -15

It is impossible to write a computer algorithm that receives another computer program and input values to it, and correctly tells you if the program will run forever or not. Assuming such an algorithm exists creates a logical contradiction.
extro...*
Posted: Mon May 22, 2006 3:17 am    Post subject: -16

I actually discovered the alleged word while in a room with about a dozen people, 2/3s Indian. That we (American English speaking people) don't even have a word that's the precise opposite of 'postpone' is perhaps scary.
Lepton*
Posted: Sun May 21, 2006 5:31 pm    Post subject: -17

East Asians (especially the Japanese) stereotypically have a strong work ethic.
wordcross
Posted: Sat May 20, 2006 4:25 am    Post subject: -18

well, they'd have to understand *why* it's a joke to want to post it.... anyone care to fill me in?
Lepton*
Posted: Sat May 20, 2006 3:30 am    Post subject: -19

Is no-one else willing to make the joke that only an East-Asian would ever think of "preponing" anything?
wordcross
Posted: Sat May 20, 2006 1:49 am    Post subject: -20

haha, postcipitation
Lepton*
Posted: Fri May 19, 2006 10:43 pm    Post subject: -21

Quote:
Could we prepone the meeting that was scheduled for this afternoon? I'd like to go home at lunch, before the postcipitation starts.
Jack_Ian
Posted: Fri May 19, 2006 9:31 pm    Post subject: -22

Prepone is a recent inclusion and is now a recognised valid English word.
Encarta wrote:

pre·pone
(past and past participle pre·poned, present participle pre·pon·ing, 3rd person present singular pre·pones)

verb South Asia
Definition:

1. transitive verb bring planned event forward: to arrange for an event to take place earlier than originally planned

2. set for earlier time: to reschedule something for an earlier time or date

[Late 20th century. After postpone]

It's in Dictionary.com too.
extropalopakettle
Posted: Fri May 19, 2006 4:51 am    Post subject: -23

Today I discovered that many English speaking Asians are under the mistaken impression that "prepone" is a word, meaning the opposite of "postpone". Example: "Can we prepone next Friday's meeting to Thursday or Wednesday?"
Lepton*
Posted: Thu May 18, 2006 3:05 pm    Post subject: -24

A good description, AT. The workaround for the quantum mechanical noise is absolutely fascinating and rather inspired.

I'm knee-deep in some statistics right now, but I'll let you know if I hit upon anything interesting.
alphatango
Posted: Thu May 18, 2006 11:14 am    Post subject: -25

Lepton, I'd be extremely interested in seeing more info and the results of your calculations when you're done. As it happens, I'm currently taking a course on gravitational wave analysis, and I'm presenting a half-hour seminar tomorrow on a relevant paper.

This one's a little more involved than Lepton's description above; I'll try to explain the idea behind the paper in simple terms. Our method of detecting gravitational waves involves a number of test masses and lasers. Because of the size of the effect we're trying to see (very, very small!), we need to worry about something called quantum noise.

This quantum noise (think "quantum mechanics") can be thought of as coming from a few different sources. One of these is Heisenberg's uncertainty principle as applied to the test masses. (This is the one that says we can't know both a particle's position and its momentum to arbitrary precision.) Even though these things have a mass of many kilograms, where we wouldn't normally expect to see quantum effects, the size of the effect we're trying to measure is so small that we have to take the uncertainty introduced by the HUP into account.

Another source of quantum noise is that introduced by lasers, which inherently rely on the principles of quantum mechanics. Now, the interesting thing is this: when you calculate the noise introduced into your measurement from the test masses and the noise introduced by the laser, you get the same expression!

So despite calculating this noise from two completely different sources, we end up with the same answer. The obvious question is whether or not they're actually the same thing. There have been varying opinions on this over the past 30 years or so, but in 2003, a physicist named Vladmir Braginsky published a paper in which he claimed to have finally laid the question to rest. His answer is this: the two are indeed different, and under some circumstances, they can add, but if we're clever, we can design our experiment so that only the noise introduced by the laser affects our experiment, and not that introduced by the quantum mechanical description of the test masses.

I'm not sure how coherent and understandable that description is -- explaining stuff is a skill I'm trying to work on at the moment. Maybe I can clear it up a bit in response to any questions.
kennykiller*
Posted: Thu May 18, 2006 7:18 am    Post subject: -26

The word "vitamin" was suggested by the polish biochemist Casimir Funk. It consists of the latin words for life and nitrogenous (vita, amin).
wordcross
Posted: Thu May 18, 2006 2:22 am    Post subject: -27

I find the concept fascinating as well, but not being a physicist, i think that this little blurb of yours is about as far as i'd be able to follow you (not to impugne upon your pedagogical abilities, but i'm just not that motivated)
Lepton
Posted: Thu May 18, 2006 12:57 am    Post subject: -28

Maxwell's Equations, which describe electromagnetiism, and Einstein's Equations, which describe general relativity (gravity) have more than a few similiarities. One of the most impressive results from Maxwell's equations is the prediction of a electromagnetic wave that travels at ~300 000 km/s (light!). Well, the equations of general relativity can do the same sorts of things that Maxwell's equations can do, and so there's been speculation for a long time about the possibility of the existence of gravitational radiation.

These gravity waves would contract and expand spacetime itself as they pass. A wave that passes through a yardstick, for example, will enlarge the yardstick in comparison with a nearby yardstick. Incidentally, this is sort of how we are searching for them. The two yardsticks are replaced with two (kilometer-long) laser beams at right angles. When the laser beams are recombined, their relative phase will tell us whether one beam travelled further than the other. There are 4-km-long beams in Washington State and near New Orleans, and 2-km-long beams in Washington State and Pisa, Italy.

However, the process of detecting these waves is very difficult because they are so weak. The best sources would be colliding black holes and neutron stars. We think that, once the current detectors are running at full steam, we should see conclusive evidence of a gravity wave roughly once every few days.

For a phenomenon that hasn't been detected, they are causing a fair bit of exciting (and funding!). One reason for this is the Hulse-Taylor binary pulsar. Pulsars are neutron stars that spin extremely fast and with an extremely accurate frequency (better than our best atomic clocks, in some cases). The Hulse-Taylor object is two neutron stars that are spiralling towards each other. As they do this, their frequency is slowing down at exactly the right speed if the energy loss from the system were due to graviational radiation being generated from the system. Pretty strong evidence, imho.

Right now, I am working on a project that involves calculating how effective the gravity wave detectors would be for determining parameters of the sources (ie: neutron star/black hole masses, orbital configuration, distance, etc). The distance is especially important, because the systems that generate gravitational radiation should be visible from extremely far away (since gravity waves don't damp out by intervening matter like light does) and thus the sources of gravitational radiation can be used to determine the evolution of the size of the universe.

If you'd like to hear more, email me or post your questions here. I think it's fascinating stuff, but i suppose that I am biased. =]
MillerTime
Posted: Mon Apr 10, 2006 2:30 am    Post subject: -29

Bump.

Here's how to build a simple low-pass filter using a resistor and a capacitor. A low-pass filter, as the name implies, allows signals with low frequencies to pass through but blocks high-frequency signals.

A capacitor with capacitance C has impedance Z = 1/sC, where s is the frequency of the circuit. So, for very high frequencies, Z --> 0 and the capacitor acts as a short circuit. Similarly, for very low frequencies, Z --> infinity and the capacitor acts as an open circuit. To take advantage of this, set up your resistor and capacitor as follows:

Code:
+   --/\/\/\---     +
R     |
Vin           ---   Vout
C  ---
|
-            ground -

At high frequencies, C will be a short circuit and Vout will be zero. At low frequencies, C will be an open circuit and Vout will equal Vin.
Quailman
Posted: Fri Jan 20, 2006 2:21 pm    Post subject: -30

I learned something interesting today. Steelhead and Rainbow Trout are the same species. It makes it quite difficult to invoke the Endangered Species Act to protect the steelhead, which can grow to 20 pounds and spends part of its life in the ocean. The rainbow trout on grows to three or four pounds and lives its entire life in fresh water.
Guest
Posted: Thu Dec 01, 2005 5:09 pm    Post subject: -31

Entertain your friends with these stupid quotes.

"Inbreeding is how we get championship horses."
- Carl Gunter, Louisiana state representative, explaining why he was fighting a proposed antiabortion bill that allowed abortion in cases of incest.

"Everything that can be invented has been invented."
- Charles H. Duell, Commissioner, U.S. Office of Patents, 1899.

"The concept is interesting and well-formed, but in order to earn better than a 'C,' the idea must be feasible."
- Yale University management professor in response to Fred Smith's paper proposing reliable overnight delivery service. (Smith went on to found Federal Express Corp.)

"Predictions are difficult, especially about the future."
- Yogi Berra, Baseball player

"Yes, maam? Right here, this lady. No, she! Yes, right, second row. Next to the guy in the blue shirt, holding her left hand up. It's a he? Sorry about that. Gotta be careful. I'm very sorry. Go ahead! I'm, excuse me, I'm very sorry. Go, ah, I, a thousand apologies, go ahead."
- George Bush Sr., Former U.S. President, at a press conference

"I have opinions of my own --strong opinions-- but I don't always agree with them."
- George Bush, former U.S. President

"It is white."
- George W. Bush, when asked what the White house was like by a student in East London

"If it weren't for electricity we'd all be watching television by candlelight."
- George Gobel

"I didn't realize I was in a Buddhist temple."
- Al Gore, former U.S. Vice President when asked about his illegal fundraising activities that took place in a Buddhist temple.

"Sure there have been injuries and deaths in boxing - but none of them serious."
- Alan Minter, Boxer

- Ted Kenneday, US Senator

"Did people build this, or did Indians?"
- Tourist question at Mesa Verde National Park
Doc Borodog
Posted: Mon Nov 28, 2005 8:20 pm    Post subject: -32

The Most Important Thing You Will Learn Today

Most modern movie theaters have two separate wings, one to the right of the concessions, one to the left. Each wing typically has its own restrooms. Furthermore, movie show times are typically staggered to reduce congestion in the lobby as films end and patrons exit the theaters. If, like me, when you exit the theater you usually have to piss like a racehorse and hate getting caught in the crowd of similarly afflicted exants, proceed immediately to the other wing and use the restroom there, since it is unlikely that a film has just ended there, and there will be no wait. I always do this, and it has never failed me.

You are welcome.
Guest
Posted: Mon Nov 21, 2005 3:29 pm    Post subject: -33

I really like the way it shows the little guy runnng away from the car. Pretty good assumption that if you ever find yourself shut in the trunk of a car, you gonna want to run like hell if you manage to get out.
extro…
Posted: Mon Nov 21, 2005 2:43 pm    Post subject: -34

Some of them glow in the dark.

Guest
Posted: Mon Nov 21, 2005 11:32 am    Post subject: -35

Sessie wrote:
Hey, my car has one of those. The handle has a little diagram of a stick figure escaping from the trunk.

How would you be able to sse that if the trunk was closed?
Chuck
Posted: Sun Nov 20, 2005 11:34 pm    Post subject: -36