# Which is hotter: **URL:** \ **Category:** Factual Questions\ **Created:** [August 5, 2005, 9:11pm UTC](https://boards.straightdope.com/t/which-is-hotter/315787 "2005-08-05T21:11:29Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [August 6, 2005, 8:50am UTC](https://boards.straightdope.com/t/which-is-hotter/315787/21 "2005-08-06T08:50:59Z")
And what is the practical difference between “current flow gives the gas atoms or molecules some extra energy which they then give up in the form of a photon” and “current flow gives the gas atoms or molecules some extra heat, lifting the electrons to an excited state which they then give up in the form of a photon”? Same difference, the current excites the electron in the atom raising it to a higher energy state. When it falls from that state it emits a photon. Precisely the same as the current heating the atom and exciting the electron to that state. Neon lights operate by direct electron bombardment for excitation rather than electron conduction so the emmison spectrum is narrower, but the process is the same: that of energy applied to an atom increasing the electronic state which allows later re-emmsion as visible light. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 6, 2005, 9:46am UTC](https://boards.straightdope.com/t/which-is-hotter/315787/22 "2005-08-06T09:46:27Z")
That’s like saying that a plane and a car are the same because they both get you where you need to go. Just because the end result is similar does not mean the mechanisms are similar, as well. In a hot object, the individual atoms or molecules all have different energy levels with a more or less random distribution, so you get a basically continuous spectrum with a distinct Gaussian curve - the so-called blackbody spectrum. In this case, the heat imparts energy to the whole atom or molecule. In electrical stimulation, the energy is only imparted to the valence electrons, and is basically the same for each atom or molecule (quantum effects smear things out so the output is not 100% monochromatic). The point is, it’s easy as a practical matter to tell the difference between light produced by incandescence and light produced by electrical stimulation. All you have to do is look at the spectra. ---
**Author:** ![spinky](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@spinky](https://boards.straightdope.com/u/spinky)\ **Post date:** [August 6, 2005, 5:58pm UTC](https://boards.straightdope.com/t/which-is-hotter/315787/23 "2005-08-06T17:58:29Z")
Damn, and here I was thinking that this was going to be a completely objective (since it’s GQ) discussion of which of two women was better looking. With pictures, of course. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [August 6, 2005, 8:30pm UTC](https://boards.straightdope.com/t/which-is-hotter/315787/24 "2005-08-06T20:30:37Z")
Hey, Q.E.D.! Welcome back! [You’ve been missed.](http://boards.straightdope.com/sdmb/showthread.php?t=320423) I hope all’s well, and that you’ll be around for a while. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [August 6, 2005, 8:31pm UTC](https://boards.straightdope.com/t/which-is-hotter/315787/25 "2005-08-06T20:31:32Z")
> [@Scott Plaid](#): > > [Iron](http://www.rpi.edu/~foutzl/Iron.html)? [Lead](http://www.rpi.edu/~foutzl/Lead.html)? Are you kidding? A better question would be [Platinum](http://www.rpi.edu/~foutzl/Platinum.html) or… that is it, I guess. Not to many metal themed babes. For once, **Scott** , I like the cut of your jib. 😃 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 6, 2005, 8:58pm UTC](https://boards.straightdope.com/t/which-is-hotter/315787/26 "2005-08-06T20:58:57Z")
Hey, thanks, **comma**. Dunno if I’ll be around quite as much as I used to, but I’ll try to drop by from time to time. Nice to see some of the old gang is still here. ---
**Author:** ![douglips](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@douglips](https://boards.straightdope.com/u/douglips)\ **Post date:** [August 7, 2005, 9:02am UTC](https://boards.straightdope.com/t/which-is-hotter/315787/27 "2005-08-07T09:02:13Z")
> [@Blake](#): > > We’re all forgetting that heat and temperature are not synonymous. Squink’s figures refer to temperature while the OP asked which is hottter. The lead will be hotter despite being the same temperature. Your post requires some correction and clarification. > [@](#): > > Heat is the amount of kinetic energy contained within an area, temperature is just the average velcocity of the particles in an area. They are the same thing if the two areas contain identicle particles, but if there are different particles or numbers of particles they aren’t the same at all. > > Lead is denser than iron. As a result the atoms can be travelling at the same average speed, and thus have the same temperature, but because they have much more mass/volume they also have more energy to impart, and are thus hotter. Temperature is a measure of the average kinetic energy of a group of molecules, not a measure of the average speed. Heat is not something that an object has, it’s usually considered something that is being transferred from one object to another. If you were to talk about the “heat” of an object, you’d be better off talking about the internal energy of the body, which is temperature times the number of molecules (times some constant.) > [@](#): > > This is the reason why a shower gets hotter when the pressure increases, despite the water being at precisely the same temperature. Higher flow rate = more particles/unit area = hotter despite temperature remaining stable. Similarly a cubic metre of air at 80oC will be just mildly unpleasant at worst, like air from a hair dryer. Immerse the same body part in a cubic metre of water at that temperature and you will scald yourself. Same temperature, totally different heat. Well, higher flow rate means more heat flowing through the shower head (i.e. heat flowing from your hot water tank to your cold shower/body.) That would mean that you might feel warmer with more water flowing over your body, just like you feel colder when the wind is blowing rather than standing still - your body has a constant supply of new surrounding fluid, whereas with less flow the fluid stays near you and cools off/warms up a little. But, water at a certain temperature will ALWAYS transfer heat to you at exactly the same rate. It’s just that if you have more water at that temperature it doesn’t have time to cool off and transfer heat more slowly. And, the difference between the heat transferred to your body from air and water is due to differences in thermal conductivity of water versus air. And once you start to transfer heat from the water/air to your body, you start to decrease the temperature of the water/air in accordance with the water/air’s specific heat. > [@](#): > > This all gets complicated because of relative thermal densities/ heat capacities and so forth, and it’s been so long since I studied this that I probably couldn’t remember how to calculate it even if I did have the figures. However I would guess that the bonding in lead is so similarly to that in iron that the thermal density is correlated pretty well to density. The only major complicating factor is that lead melts before it goes red, and the resulting free energy change probably means it’s even hotter at these temperatures than density alone predicts. Thermal density? What’s that? I think maybe you mean specific heat. And, for metals, it appears that molar heat capacity is about the same, which means that heat capacity in metals depends on atomic weight as well as density. Iron has both a higher specific heat and a higher thermal conductivity than lead, meaning I’d rather touch a hot lead thing than a hot iron thing of the same mass. Lead is only about 50% denser than iron, but has 1/3 the specific heat of iron. So, I’d also rather touch a hot lead thing than a hot iron thing of the same volume. I do not know whether molten lead would have much different thermal conductivity than solid lead, but one thing to keep in mind about touching liquids is you have more ways to get heat into you than with solids - just as in your shower or in a wind, flowing fluid gives better heat transfer because you have fresh hot stuff to burn you. Here are some links to help refresh your memory of physics: [Properties of Iron](http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/fe.html) [Properties of Lead](http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/pb.html) [Hyperphysics: Heat and Thermodynamics](http://hyperphysics.phy-astr.gsu.edu/hbase/heacon.html#heacon) [Previous page](https://boards.straightdope.com/t/which-is-hotter/315787.md?page=1)