Talk:Joule

Conversions

The Conversion factor : TJ/kcal 4,187E-09 is used in the UNFCCC. Can anybody find out where that factor and the factor used in wikipedia came from = Units defined in terms of the joule include:

   * 1 thermochemical calorie = 4.184 J
   * 1 International Table calorie = 4.1868 J

? —Preceding unsigned comment added by SvenAERTS (talk • contribs) 02:43, 25 October 2008 (UTC)

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)

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).

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?

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)

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)

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)

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)

No, it's not. It's the work required to accelerate one kilogram to a speed of ${\sqrt {2}}$ 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 force of one newton. --Shastra 16:57, 20 August 2006 (UTC)

==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)

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)

Person, droplet, beer

1 joule is approximately equal to: [...]

• 1/100th of the energy a person can get by drinking a single droplet of beer.

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)

When you say "1600-1900 kJ/L" are you talking about an American "Lite" beer which is less than 6% alcohol or an European beer which is over 12% alcohol? —Preceding unsigned comment added by 76.186.80.92 (talk) 06:15, 31 December 2007 (UTC)

This is the "typical" section. These are typical measures. A typical beer has somewhere around 1700kJ/L. Not lite beer, not low-cal beer, not Elephant beer. Just a typical beer. Also, I like how Shastra's working backwards arrived at the volume of the droplet to be precisely the value of a metric drop (unit). Droplets also have typical sizes, and in fact, a "drop" has various similar measures that compare favourably to the size of a droplet of liquid, like beer. A typical droplet of typical beer contains about 100J. To describe the size of the droplet completely spoils the point of the section! LightYear (talk) 23:10, 1 January 2008 (UTC)

Is there a reason "beer" was changed to "water"? I don't believe water has any Calories, or at least not nearly as much as beer, so this should be reverted. —Preceding unsigned comment added by 139.85.239.112 (talk) 14:54, 1 October 2008 (UTC)

Done - you're quite right. Can we protect a single sentence? rv'ing the same sentence every month or so is getting tiresome. LightYear (talk) 06:12, 7 October 2008 (UTC)

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)

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)

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)

Is the description missing something?

The description says "a force of one newton moving an object one meter along the direction of the force". Shouldn't that be "a force of one newton moving a one-kilogram object one meter along the direction of the force"? --Musanim 16:43, 3 June 2007 (UTC)

No. The newton already takes care of the weight of the object. It could be a 100kg object being pushed on non-ideal rollers, or a 0.1kg object being pushed vertically, as long as the resulting force is 1 newton. LightYear 03:03, 4 June 2007 (UTC)

I'm not getting something here. What if a force of 1 newton were applied to an object with very little mass; wouldn't it just accelerate more quickly than a more massive object (and traverse 1 meter in much less time)?--Musanim 01:35, 5 June 2007 (UTC)

Indeed, one newton applied to a very light object will have that object moving at a terrific (change of) pace by the end of the metre. The kinetic energy (0.5mv^2) gained by the object (1J) during the event will still be the same as that of a slower moving, heavy object (which underwent the same 1N force along a metre). Joule is a measure of energy, not velocity or power (both of which involve time, as you are expecting). There's probably a better forum for this - study some physics sources, and the initiallly counter-intuitive concept will click for you. LightYear 05:21, 5 June 2007 (UTC)

The newton unit already takes into account the mass of the object. F = ma, and 1 newton == 1 kilogram * 1 m/s^2. So a given force, say one newton, can accelerate a large object slowly, or a small object quickly. Foobaz·o< 06:01, 6 June 2007 (UTC)

After thinking about this for a while, I finally got it. At first, it seemed that a 1 kilogram object being pushed with a 1 newton force for 1.414 seconds to move it a meter had to involve more work than a 1 gram object being pushed with a 1 newton force for 0.0447 seconds to move it a meter. But then I considered what might apply such a force, and I imagined a second object being acted on by gravity (pulling at right angles to the first object, through a pulley). Since the second weight falls the same distance in both cases, the same work is done. QED. Thanks for your help.--Musanim 01:30, 8 June 2007 (UTC)

SI multiples

I have nominated Template:SI multiples (transcluded or subst'ed in this article) for deletion on WP:TFD. Han-Kwang (t) 16:07, 23 August 2007 (UTC)

• This issue arose because of a dispute (see discussion here) over the inclusion of table of SI-prefixed versions of the kelvin in the Kelvin article. Somone didn’t see the value of it and simply deleted it (notwithstanding that an editors’ note warned of other articles that linked directly to the table). That table lists the full range of the kelvin’s SI-prefixed forms. An individual SI table placed in each article on units of measure serves a purpose that a general link to SI prefixes can't do: as demonstrated in the Kelvin article, it shows which prefixed versions of the unit in question (in bold) are the common ones that one might want to limit themselves to to avoid using those that are overly obscure.

  There’s another—and more important—consideration: These tables prevent bloat in articles by avoiding having to explain units of measure in each article that uses them. For instance, the Absolute zero article (as do other articles) might mention a 450 nk record-cold temperature. Note the “nk” link in this just-cited example. It takes the reader to the table where one can see the magnitude of the value in relationship to others. The same thing is done when an article uses “nm” (nanometer) or “µg” (microgram) in a technical article or . Articles would become bloated if they each had to individually explain every prefixed form of a unit of measure. Yes, one can use scientific notation. But this sort of stuff quickly starts going over the heads of many readers depending on the nature of the article and how soon in the article it begins using scientific notation; that is, after all, one of the purposes of SI prefixes: to simplify. These tables have been in articles for years now and have served a most useful purpose. Just because someone doesn’t see the value in a template is no justification for deleting it. If they don’t see the value of it, don’t use it. And please stop deleting or truncating the tables; it breaks links to it in other articles. Greg L (my talk) 21:06, 23 August 2007 (UTC)

Book mass and height?

"The amount of energy released if a single textbook is dropped." I have had textbooks which have mass from 0.5 kg to 5 kg.

That's nice. And what was your typical textbook weight, approximately? Somehow, I think the 5kg textbook was something of an anomaly! LightYear (talk) 23:10, 1 January 2008 (UTC)

And, how about the height of this drop? I know that e=mgh should hold here on earth near sea level. Reddwarf2956 (talk) 06:54, 31 December 2007 (UTC)

What height would a textbook typically be dropped at? About the height of a human hand? Working backwards, it looks like they might be using a light textbook (0.5kg for a paperback is reasonable) and a small drop (20cm from hand to desk, or bag to floor, say). These seem like reasonable, typical values for weight and drop distance, and the result is a handy story for appreciating a joule. This is not the precision section, this is the approximate, "real life" section! And, incidentally, the statement has a reference if you want to chase it up with its original author. LightYear (talk) 23:10, 1 January 2008 (UTC)

Effect of gravity?

Does moving one newton one meter along a direction expand 1 joule in space as well as on Earth? In other words, does gravity make a difference? There's no mention of that here, and it something that your average reader will want to know ... I'm no physicist. 67.189.104.78 (talk) 19:54, 8 September 2008 (UTC)

You wont expend a joule, because the movement wont require a Newton, unless the force acts against resistance. The resistance is often gravity but it doesn't have to be. You could be on the moon and pushing an object through honey. Does that clear it up for you? If you could rephrase it in your own words, perhaps we could come up with a worthwhile inclusion for the article. LightYear (talk) 00:35, 9 September 2008 (UTC)

Pronunciation

how should it be pronounced?