how accurate is Drake's Equation?
100416
Not very.\n\nThe Drake Equation is supposed to estimate the number of civilizations in the Galaxy, and is usually written as:\n\nN = R* fp ne fl fi fc L\n\nwhere,\n\n    * N = The number of communicative civilizations\n    * R* = The rate of formation of suitable stars \n    * fp = The fraction of those stars with planets. \n    * ne = The number of Earth-like worlds per planetary system\n    * fl = The fraction of those Earth-like planets where life actually develops\n    * fi = The fraction of life sites where intelligence develops\n    * fc = The fraction of communicative planets \n    * L = The "lifetime" of communicating civilizations\n\nA problem is that one can come up with other criteria, which add a term and tend to lower the estimate. For example, fraction of Earth-like worlds with a large Moon, or the timespan when an "echo" or a civilization (buildings, spaceships, etc.) can be detected before fading away.\n\nThe reason is that there is so much uncertainty in most of these values. Until that part is nailed down we won't really know which of these terms are critical, which not, and what other terms (if any) to add.\n\nNevertheless it is an easy way to guestimate some of the concerns with the possibilities of alien civilizations.
81560
balanced is the best answer, although constant would be correct as well....or if you're looking for a numerical answer, it would be 0
251207
Don't have it handy,but it'sjust a little denser than water, from what I remember. Check www.nasa.gov. They have lots of planetary info!
796759
You'll actually make the measurement worse. Think about the math without going in to numbers too much. Let's say we have 30 arms (yeah, I know, too many). Only one of them at a time is nearly perpendicular to the wind force. It's plus/minus 6 degrees. By the time that one move past that 6 degrees the next is coming in. Think about the sines and cosines - the force parallel and perpendicular - nearly 100% is going in the direction of the wind. It moves that blade just about right.\n\nNow go from 30 to 3 blades.Each blade now covers 120 degrees. That makes them the most perpendicular plus/minus 60 degrees. Now look at the sines and cosines of the forces. You actually get quite a bit of force slowing down your reading. If you hooked up your anemometer to an o'scope, you would see a pretty drastic fluctuation in speed variance. The more arms, the flatter that variance becomes.
1051217
From the daily racing form, link listed below. It was answered my Andy, so I am pretty confident it's accurate.\nAndy Beyer: \n\n"My rough rule of thumb is to subtract 14 points from the Timeform numbers; that works reasonably well--at least for upper-level horses of the sort who come to the Breeders' Cup. As horses get cheaper, the difference between the two scales is narrower. "
478107
It is called the equation of time. It isn't really statistics though.
759307
here we go  kinetic energy at point of shot equals potencial energy at top of the squirt\n\n1/2 m v^2 = mgh\n\nm's cancel  (Rained in seattle)\n\nv = Square root (2gh)\n\ncheck my algebra... Note, you must change cm to meters before you can answer
698836
I do not believe this is accurate information.\n\nBlessed Be
757410
This equation only works for small angles theta < 10 degrees\n\nPeriod = 2*pi * sqrt (length / g)\n\nThe period in an undamped simple pendulum does not depend on mass.\n\nThere is a more in depth formula for larger angles on hyperphysics.
237929
You take lots of measurements of wind velocity, temperature and barometric pressure at many grid points, each of which defines a "cell" (a small volume of air -- small compared to the size of the hurricane, that is). From pressure and temperature you can estimate density of each cell, and from the cell volume, the cell's mass. Kinetic energy = 0.5*M*V^2.  Compute for each cell and add 'em up.
388135
since it is difficult to use the equation writer on Yaho answers, I am giving you a link, that has the answer.\nhttp://homepage.mac.com/nshoffner/nsh/CalcBookAll/Chapter%206/Ch6DefInt.htm\nScroll down a little.
1086900
Yes it is true for x=200.62 degrees.\n\nCarefuly schetch tan(x) and sec(x) [sec(x)=1/cos(x)] and you will see the answer or let your fingers do the calculator walk :).\n\n\nWas that helpfull?
814756
or_try_this is correct.  It is dense, and a 30-inch column of mercury fits in a laboratory better than a 34-foot column of water.  It is stable and doesn't evaporate at room temperature.  Its thermal expansion can be compensated for, but it's usually small compared to the pressure differences it's measuring.  It looks scientific, too.
1072544
there is no exact figure as earth follows an elliptical path and it is at different distances from sun at different times.\nbut on an average 8* 60*c meters    where c is speed of light
1125677
The Drake Equation provides a useful way of thinking about these issues,\n\nThis equation was devised by Dr. Frank Drake (a professor at the University of California, Santa Cruz) in the 1960s in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of extraterrestrial civilizations. In recent years, the Rare Earth hypothesis, which posits that conditions for intelligent life are quite rare in the universe has been seen as a possible refutation of the equation.\n\nThe Drake equation states that:\n\nN (the number of civilizations in our galaxy with which we might expect to be able to communicate at any given time) is the product of the following factors: \n\nR* which is the rate of star formation in our galaxy \nfp which is the fraction of those stars that have planets \nne which is the average number of planets that can potentially support life per star that has planets \nfl which is the fraction of the above that actually go on to develop life \nfi which is the fraction of the above that actually go on to develop intelligent life \nfc which is the fraction of the above that are willing and able to communicate \nL which is the expected lifetime of such a civilization \n\nNB the Drake Equation only considers the 200-400 billion stars in our galaxy, as the issue is being able to communicate with them, and stars in other galaxies are considered too far away for that. However there are billions of galaxies and that increases the probability of intelligent life elsewhere in the Universe considerably.\n\nThe rare Earth hypothesis asserts that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely combination of astrophysical and geological circumstances. Hence such life is probably very rare in the universe. The rare Earth hypothesis is explained in detail in the book Rare Earth: Why Complex Life Is Uncommon in the Universe, by Peter Ward, a geologist and paleontologist, and Donald Brownlee, an astronomer and astrobiologist.\n\nThe rare Earth hypothesis is the contrary of the principle of mediocrity, also called the Copernican principle, whose best known recent advocates include Carl Sagan and Frank Drake. The principle of mediocrity maintains that the Earth is a typical planet in a typical planetary system, located in an unexceptional region of a large but conventional spiral galaxy. Ward and Brownlee argue to the contrary: planets and planetary systems that are as friendly to complex life as are the Earth and its solar system, are probably extremely rare in the universe. The Earth could well be the only planet in our galaxy, the Milky Way, and even in the entire universe, bearing complex life.\n\nIf complex life can evolve only on an Earth-like planet, then the rare Earth hypothesis solves the Fermi paradox (Webb 2002): "If extraterrestrial aliens exist, why aren't they obvious?" There is no evidence of aliens because none exist in the Milky Way. Hence the current lack of evidence of extraterrestrial civilizations.\n\nThe rare Earth hypothesis approaches the issue of habitable planets like this:\n\nThe galactic habitable zone\n\nA great deal of the known universe cannot support life because of elementary astrophysical and chemical considerations. Rare Earth refers to such regions as "dead zones." The exceptions make up the galactic habitable zones, the result of opposing tendencies that are a function of distance from the galactic center. As that distance increases:\n\n(1) The metal content of stars declines. Because metals are the fundamental building blocks of life, the likelihood of life is a decreasing function of distance from the galactic center. \n\n(2) The X-ray and gamma ray radiation from the black hole at the galactic center, and from nearby neutron stars and quasars, bec
342329
Well, I think I found something; it says that the rule is part of the Newton-Cotes formulas (Isaac Newton and Roger Cotes).\n\nThis is the page where I found the info:\nhttp://www.absoluteastronomy.com/ref/trapezium_rule
844938
The predicted figure is accurate but its accuracy depends on the size of the sample.The half life of an atomic species is an average figure based on a reasonably sized sample with a huge number of atoms. It's based upon the probability that any given atom will decay at a given time. For instance scientists can predict that a coin has a 50/50 chance of landing heads or tails when flipped. This means that if you flipped the coin 1000 times you could be reasonably certain that you would get close to 500 tails and 500 heads. This doesn't mean that if you flipped it four times you would get 2 heads and 2 tails each time. It's the same with the rate of decay. The decay occurs randomly in that scientists cannot predict when any given atom will decay anymore than you can predict exactly which flips will result in heads or tails. But the more atoms a sample has the more accurate the predicted rate of decay (half life).