Talk:Joule
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under the earth's gravity
Unless you are Neil Armstrong et al probably you have no choice.
But if you really want to pick nits: You could be located in an elevator in Empire State building where the cables have all broken. Or perhaps riding a roller coaster.
Egil 09:26 Apr 9, 2003 (UTC)
What´s the equivalence between a Kwh and a Joule ??.
- see the article. I've added the information. :-) -- Tarquin 19:02, 20 Aug 2003 (UTC)
[edit] Time to raise apple misleading
this article sucks The article currently says: "One joule is also the work done to produce power of one watt for one second, such as when somebody takes one second to lift the small apple mentioned above through one metre under the earth's gravity."
Surely this is misleading. Assuming that the apple is at rest before and after its gain in altitude, the joule of energy is required because of the increase in its gravitational potential energy. If the time taken is to be relevant, then we would have to be talking about an apple undergoing a net acceleration, which should be in a horizontal direction to simplify things.
- It is misleading. The time to lift that apple is irrelevant; for work against gravity, W = mgh (in the example, (0.102 kg)(9.8 m/s²)(1 m) = 1 J). No time factor involved. The connection should not be to the joule as a watt-second, but rather to the joule as a newton-meter. You could make a different example involving acceleration, of course. Gene Nygaard 13:06, 9 August 2005 (UTC)
-
- Yes, in fact specifying a time to raise the apple's potential energy gives you a value of power (e.g. J/s). Not sure what the original sentence was trying to demonstrate, but it is wrong as it currently stands (or belongs in the article on the Watt).
[edit] Too little data and too many sections
This article contains too many sections yet too little data and I've made some rearrangements in the previous edit. The article needs more useful data rather than just conversions. Perhaps someone could add practical examples of use, or more history regarding the subject (e.g. Metre).
Should the definitions of Kilojoule and Megajoule be in a different article?
[edit] Electron-Volt conversion
It would be useful to add a conversion to electron volts here for the aspiring or forgetful nuclear physicist. 1 [J] = 6.241506363 x 10^18 [eV] AtomBum 01:22, 7 October 2005 (UTC)
- I second that motion! It is done. mastodon 09:59, 4 November 2005 (UTC)
[edit] My attempt at clarification
I recently attempted to clarify the conversion section and my changes were promptly reverted. The section in question now reads (excerpting):
"1 joule is equal to: ...
- 4.184 J – 1 thermochemical calorie (exact)
- 4.1868 J – 1 International Table calorie (exact)"
That does not make sense in English. Also the abbreviation "c." is used in some places, presumably to mean approximately, but not in others where the conversion factor is just as approximate. The usage should be consistent and it seems to me better to just say "approximately" than use an abbreviation that many readers may not be familiar with. In any case, summary reversion without discussion does not seem appropriate for a serious edit. --agr 23:09, 16 November 2005 (UTC)
- Nor is just throwing out those two lines because you cannot figure out how to reword them appropriate to a serious edit. The point is that this is the direction in which the conversion can be expressed as a terminating decimal fraction, without resorting to common fraction with a decimal fraction denominator such as 1/4.184, or even less comprehensibly reducing that to a proper fraction of 125/523. Gene Nygaard 00:12, 17 November 2005 (UTC)
I didn't throw them out, I put them in a separate section in an attempt to make it clear what was being said:
"Also:
- 1 thermochemical calorie = 4.184 J (exact)
- 1 International Table calorie = 4.1868 J (exact)"
Look, we all make hasty mistakes occasionally, but please at least read an edit carefully before reverting it. --agr 00:58, 17 November 2005 (UTC)
[edit] Joules--KiloJoules
I came to this page looking for the conversion for kilojoules to joules. I couldn't remember which power of ten they were related by. seeing as you have all those other conversions (including beer!) might you add kJ to J?
- 1 kJ = 1000 J. There was a table of all the SI conversions, but it provoked considerable controversy. I never understood why it did harm if it was at the end. Also, I'd raise the question of whether most of the conversions wouldn't be clearer the other way around, e.g. kilowatt-hour = 3600000 J vs 2.7778×10−7 kilowatt-hour, human generates 100 J per second, etc. Most people have no intuitive sense of scientific notation, if they understand it at all. Doing so would also make it clear that litre-atmosphere and BTU are both about a kilojoule, a useful rule of thumb. The apple rule could be stated separately (and we only need one version). --agr 12:24, 10 March 2006 (UTC)
[edit] joule and newton
The following quote is confusion joule and newton. I'll delete it. "One joule is also: The work required to accelerate one kilogram at a rate of 1 m·s-2 " Bo Jacoby 09:05, 24 March 2006 (UTC)
m·s-1, regardless of the rate of acceleration. One kilogram that is accelerated at a rate of 1 m·s-2 corresponds to a ==not sure what to do with this - should this be deleted?
the energy required to lift a small apple 10 centimetres (1/10 metre) by converting the heat that the quiet person produced, on a hundredth of second, in work, with 10% efficiency.
- Yes, please remove it or change it. I don't know exactly how our muscles convert food into mechanical energy, but when it happens we use up more food energy than the basic 100 joules of "idling" energy that is converted to heat. So the calculation would be different. I think a more understandable example would be something like "one joule is the energy expended while walking 5 millimeters" (if that number is correct). --Shastra 17:47, 20 August 2006 (UTC)
[edit] Joules & People
I noticed this randomly, but unless I missed something, if a person (who is still) expended 1 joule worth of energy in heat every one-hundreth of a second, they would burn (((1 * 100) * 3600) * 24) = 8,640,000 (kilo)calories per day on heat alone. Also, is it correct to say that we (humans) 'produce' energy when we do things? I think it's more correct to say that we 'use' energy. HunterXI 21:02, 10 August 2006 (UTC)
- That's 8,640,000 joules. To get kilocalories ("food calories"), multiply by the conversion factor 2.390×10-4 and you get 2064.96 kcal. And yes, we don't really produce energy. We convert the chemical binding energy in food molecules into heat energy and mechanical energy. --Shastra 17:47, 20 August 2006 (UTC)
[edit] Person, droplet, beer
1 joule is approximately equal to: [...]
Er, no. Not without a quantifiable scientific definition of "person", "droplet" and "beer". This one should be deleted, no?
-
- That statement surprised me also at first. But it does say approximately... And the definition of "person" is irrelevant, as long as it is a creature that can oxidize the hydrocarbons contained in beer. For the definition of "beer", it's a reasonable assumption that it's a beer brand within the very common range of 1600-1900 kJ/liter. The definition of "droplet" is more fuzzy, but calculating backwards the beer droplet size must be about 50 microliters (a ~5mm sphere) to contain 100 Joules of food energy. Perhaps this droplet size should be mentioned. --Shastra 07:43, 26 September 2006 (UTC)
[edit] why is there no info on James Prescott Joule
i can only assume they're named after him EDIT: my bad, i see it now —The preceding unsigned comment was added by 71.245.246.231 (talk) 01:08, 3 January 2007 (UTC).
[edit] Surface area
Are joules related to surface area? Someone is telling me that a joule is an amount of energy per centimeter of surface area, which is different than what I understand, but I've never had a physics class. Some guy 16:26, 9 January 2007 (UTC)
- The talk page is not for asking physics questions, but no. LightYear 01:24, 17 January 2007 (UTC)
[edit] Introduction
I've changed the introduction to match the style used in newton. I picked this style because it addresses a few issues: strict, succinct definition; etymology; and unit status. I then followed with the existing practical definition, making a few changes: made the distinction between J and Nm more obvious; removed jarring juxtaposition of "absolute minimum" and "rough guide"; and removed "just under" from "just under 10cm" because its wrong and unnecessary (we're talking understatement by ~0.2cm depending on elevation). LightYear 01:24, 17 January 2007 (UTC)
[edit] Pronounciation
Somebody should put the pronounciation at the begining of the article.
It's pronounced "joole", but not eveybody knows that (I didn't for quite an while actually).
I would put it myself, but I don't know how to write with those fancy phonetic letters. Nor would I know which ones to use.
You know what... I am gonna just write "(pronounced 'joole')" and one of you guys fix that later. —The preceding unsigned comment was added by 200.164.220.194 (talk) 09:37, 29 January 2007 (UTC).
- Good point, thanks for the contribution. I've updated it to the standard IPA definition. Slightly uncomfortable about the multiple parentheses making it difficult to parse the first sentence, but think it is probably okay. --LightYear 01:36, 30 January 2007 (UTC)
Maybe a silly question, but why French pronunciation when James Prescott Joule was an Englishman? --Kompik 17:51, 31 January 2007 (UTC)
- Seems like a good question to me, but I'm in no position to give you an answer. I do have a counter question for you though - how would it be pronounced by an Englishman? --LightYear 02:46, 1 February 2007 (UTC)
I've tried Google search [1]. Merriam-Webster mentions both pronunciations: dzu:l and dzaul. First glance at the first results from this google search suggests that most dictionaries use the pronunciation dzu:l. Wikipedia article James Prescott Joule mentions
- It seems that the pronunciation of the name Joule was not really standardized during the scientist's lifetime and that his family's brewery even used this confusion for a rhyming ad: Whatever you call it... it's GOOD!
--Kompik 11:26, 1 February 2007 (UTC)
