User:Wolfkeeper/scratch

a
Consider a small length of rotor, of length l, mass m, rotating around curve at $$\omega$$, radius of curvature r

1. $$F = m r \omega ^2 $$

2. $$V = r \omega$$

3. From 1 and 2: $$F = \frac {m V^2} r$$

4. $$m = \rho l$$ where $$\rho$$ is the mass per unit length and l is the length

5. therefore: $$F = \frac {V^2 \rho l} r$$

6. from 2: $$F = \frac {V^2 \rho l} {\frac {V} {\omega}} = V \rho l \omega$$

7. but $$\omega = V c$$ where c is the curvature per unit length in radians/m

8. therefore: $$F = V^2 \rho c l$$

9. therefore $$F/l = V^2 \rho c$$


 * $$y = A sin(\omega x)$$
 * $$dy/dx = \omega A cos(\omega x)$$
 * $$d2y/dx2 = -\omega^2 A sin(\omega x)$$
 * $$\frac {d^2y} {dx^2} / y = -\omega^2$$

but $$f = -ky$$

hence $$k = \omega^2$$


 * $$ky / l = V^2 \rho \omega^2 A sin(\omega x)$$

peak:


 * $$k/l = V^2 \rho \omega^2$$


 * $$p = e^{-iwt - kx}$$
 * $$dp/dt = -iw p$$
 * $$E = w^2 p^2$$


 * $$\frac {d^2p} {dt^2} = w^2 p$$
 * $$\frac {dp} {dt} = -k p$$
 * $$\frac {d^2p} {dt^2} = k^2 p$$

Etymology


The word "encyclopaedia" comes from the Pseudo- Classical Greek "ἐγκύκλιος παιδεία", transliterated "enkyklios paideia"; "enkyklios" meaning "cyclical, periodic, or ordinary", and "paideia" meaning "education". Together, the phrase literally translates as a "[well-]rounded education", meaning "general knowledge". Copyists of Latin manuscripts took this phrase to be a single Greek word, "enkuklopaedia", with the same meaning, and this spurious Greek word became the New Latin word "encyclopaedia", which in turn came into English. Though the notion of a compendium of knowledge dates back thousands of years, the term was first used in the title of a book in 1541 by Joachimus Fortius Ringelbergius, Lucubrationes vel potius absolutissima kyklopaideia (Basel, 1541). The word encyclopaedia was first used as a noun in the title of his book by the Croatian encyclopedist Pavao Skalić in his Encyclopaedia seu orbis disciplinarum tam sacrarum quam prophanarum epistemon (Encyclopaedia, or Knowledge of the World of Disciplines, Basel, 1559). One of the oldest vernacular uses was by François Rabelais in his Pantagruel in 1532.

Several encyclopaedias have names that include the suffix -p(a)edia, e.g., Banglapedia (on matters relevant for Bengal).

In British usage, the spellings encyclopedia and encyclopaedia are both current. Although the latter spelling is considered more "proper" by British speakers, the former is becoming increasingly common in British English, in part due to the spread of American English. In American usage, only the former is commonly used. The spelling encyclopædia&mdash;with the æ ligature&mdash;was frequently used in the 19th century and is increasingly rare, although it is retained in product titles such as Encyclopædia Britannica and others. The Oxford English Dictionary (1989) records encyclopædia and encyclopaedia as equal alternatives (in that order), and notes the æ would be obsolete except that it is preserved in works that have Latin titles. Webster's Third New International Dictionary (1997–2002) features encyclopedia as the main headword and encyclopaedia as a minor variant. In addition, cyclopedia and cyclopaedia are now rarely-used shortened forms of the word originating in the 17th century.

Wikipedia is an encyclopedia
There's a theoretical issue with WP:Wikipedia is an encyclopedia which seems to be having practical consequences.

The problem is that the policy basically says that Wikipedia is an Encyclopedia, but there's no adequate definition on what an Encyclopedia is. I mean it isn't simply a compendium of the world's knowledge because lots of things are knowledge but aren't included, we don't include unreferenced knowledge, and most people seem to agree that at the very least a lot of dictionary words aren't really valid subjects for articles; and we don't have knowledge like actual train timetables here, although we do have articles on the general concepts.

So I certainly agree that the Wikipedia is a compendium of knowledge, but the definition doesn't really go far enough; plenty of compendiums of knowledge aren't encyclopedic.

I think the problem is traceable to the state of the Encyclopedia article, which doesn't really nail it.

By way of contrast, the French wikipedia have basically decided what encyclopedia means to them and stated it in the policy, rather than rely on their (equally dubious) encyclopedia article:

French Wikipedia:Wikipedia is an Encyclopedia (google translation).

It now looks like they've marked a lot of the other policies (like the french version of WP:ISNOT) as essays. In other words, I think they've simplified policy down by actually working out a theory of what an encyclopedia is, stating it, and then expecting people to follow it.

I think that historically the English wikipedia wasn't quite so sure what they're doing, and so we have a mess of pages saying that it's not this or that, but without ever actually saying what it is. This is somewhat a problem.

Most people don't seem to have that much of an idea what an encyclopedia is, so when you tell them that's what Wikipedia is, what are they supposed to do with that information?

The problem is made worse because there aren't any other references on what an encyclopedia is; this means that the Encyclopedia article fails to define it as well; but the policy page in the English wikipedia tries to reference that to define what an Encyclopedia is; but it fails to do so.

The french solution works because they (in a mild sense) OR up a definition. If you tried to fix the Encyclopedia page then it will probably get deleted, but OR is allowed on policy pages.- Wolfkeeper  02:43, 8 March 2010 (UTC)

AFD
The article is about the letters 'N' 'E' 'G' 'R' and 'O'; the circumstances that they are used together, and the history of where they were used, and any controversy around their use. There's nothing wrong with that... in a dictionary. This is an encyclopedia; and here the articles should be about an underlying topic; the topic; presumably people with melanin-rich skin, and their history and culture. But black people are covered in a different article already. There's nothing in this particular article that isn't or shouldn't be covered in the dictionary; the dictionary is specifically about etymology and usage of terms. The policy is Wikipedia is not a dictionary which forbids articles on terms, as opposed to a topic that is not a term, such as black person.

Articles on different meanings of words are allowed in the wikipedia, but only as a disambiguation page that points to the actual articles.

If you doubt this, go to the article now Negro and check this, then come back and vote DELETE.

To the degree that the subject of the article is about black people, thus the article is a wp:content fork of black person and so it should be merged back to the parent article.

A few people may be tempted to say 'no- this article has done enough'. To this I say- there's no such 'done enough' policy. If you know of such a policy please point us to it, otherwise you are simply making a null vote. In any case, an article on a term has practically nowhere to go- it covers the term, usage and etymology, and anything else is off-topic, so the article cannot be significantly improved; it cannot ever do enough!.

Some other people will say, we have WP:OTHERSTUFF that is also about terms. To that I say, yes, but we're working on that; if everytime we had an exception to a rule you weren't allowed to correct that, then no policy would ever stand. The AFD process is specifically supposed to be following wikipolicy, not following other AFDs.

There's also the question about the deprecated nature of the term; the term is currently not in widespread use; therefore, the term is far less notable- perhaps if it was a particularly notable term in widespread use it might be kept in the wikipedia (policies are not mandatory); but I see little sign of this currently. But we're also not censoring anything; the term negro still needs to be mentioned in black person; we're just not having a whole article about it; why on Earth would we want an article on a word when we have wiktionary?

This unsavoury dictionary article is undeserving of continued presence in our fine Encyclopedia! The Wikipedia is not a dictionary!!! I'm therefore calling for people of the wikipedia to do the right thing here; to TRANSWIKI-DELETE.- Wolfkeeper  03:36, 13 March 2010 (UTC)

re
Consider the body of the rocket. Let the speed of the rocket at any instant be V and the remaining mass of the rocket at any instant be M:

From Newton's second law:


 * $$T = M \frac {dV} {dt}$$

Now, consider the propellant leaving the rocket.

At any instant then the propellant is being burnt at a rate of $$\frac {dM} {dt}$$ and is leaving with constant speed $$V_e$$. Hence from Newtons second law:


 * $$T = \frac {d (V_e M)} {dt} = V_e \frac {dM} {dt}$$

where T is the thrust on the exhaust and (from Newton's third law) on the rocket.

Hence:


 * $$V_e \frac {dM} {dt} = M \frac {dV} {dt}$$


 * $$V_e dM = M dv \,$$


 * $$\frac {dv} {dM} = V_e \frac 1 M$$

Integrating with respect to M:


 * $$ V = V_e ln(M) \,$$ where M goes from $$M_i$$ to $$M_f$$ and V goes from $$V_i$$ to $$V_f$$


 * $$ V_f - V_i = dV = V_e ln (M_f) - V_e ln (M_i) = V_e (ln (M_f) - ln (M_i)) \,$$


 * $$ dV = V_e ln(\frac {M_f} {M_i})$$