Science desk
< November 2	<< Oct \| November \| Dec >>	November 4 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 3

Empty calories

I read a statement by a Dr. Rosen in an article on yahoo!life[1]. She states that diet sodas "are loaded with empty calories". Is that true? Thank you. Hevesli (talk) 10:22, 3 November 2022 (UTC)[reply]

According to Coca-cola, their diet coke has only one calorie per 330 ml can, so more just empty I would have thought, apart from E numbers. Mikenorton (talk) 10:42, 3 November 2022 (UTC)[reply]

I wonder if that particular quote was taken out of context by the article writer. It would seem to apply better to non-diet drinks. Alansplodge (talk) 13:51, 3 November 2022 (UTC)[reply]

Yes, the usual meaning of "empty calories" is calories consumed without benefit of any other nutrients such as vitamins or protein. Abductive (reasoning) 03:50, 4 November 2022 (UTC)[reply]

Cooling hot oven racks

Situation: I start heating up my oven, and at one point take two oven racks out when they are quite hot. I hold one with my one hand steadily (in a mitten), and another with another hand (in mitten), shaking it vigorously so that the individual rods vibrate. Will there be an appreciable difference in cooling rate between the two? --Ouro (blah blah) 18:09, 3 November 2022 (UTC)[reply]

The "standard equations" for such scenarios tend to be large and painful to solve. I pulled up my go-to reference - Incropera et al., Fundamentals of Heat and Mass Transfer, (my copy is a 7th edition). As you would expect, arrays of long-cylindrical-metal-rods are solved around Page 618. Rather than quote a complicated equation out of context, it's worth saying that the math is complicated. It would take six hundred and seventeen pages of preparatory explanation to do it justice (... that's why this equation is on Page 618). "Will there be an appreciable difference in cooling rate?" Yes. "Exactly how appreciable?" ... So, let's break this down: what is the metal made of? What is the air made of? How hot is the metal? How hot is the air? How precisely can you measure temperature? How many places (throughout your scenario) are you using a simplifying assumption? (Did you extract the rail from the oven in zero seconds, or in finite time? Is air viscous, or not viscous? When a steel rod vibrates, to what extent do you assume the displacement to be infinitesimal? Exactly how round are the metal rods that constitute your oven-rack?) We can literally (literally) spend hundreds of pages - hundreds of thousands of complicated mathematical words to talk about all the details. Golly, even I had to actually look up Nusselt number to refresh my memory - and I'm some kind of scientist - not just anyone, either - I happen to be the original author of the Official Wikipedia Science Reference Desk Mathematical Model And Numerical Simulator For How Much My Coffee Has Gone Cold As I Expend Time Answering Thermal Physics Questions On The Science Reference Desk!

The more pertinent questions revolve around a more general question: which of these complicated details of engineering and physics are relevant to your scenario?

Are you simply baking cookies? Few of these details materially affect the quality of your cookies.

Nimur (talk) 18:34, 3 November 2022 (UTC)[reply]

And don't forget that by shaking one hand, you are likely causing minor vibrations in the rest of your body so that the other hand is not "steady". AND the waving of the one rack will produce air currents that will blow past the other rack..... --User:Khajidha (talk) (contributions) 18:55, 3 November 2022 (UTC)[reply]

Nimur... I do not need to be baking anything, that's just something I thought of... I just wondered... I can appreciate the diversity of variables that need to be taken into account and am thankful for Your answer - doing justice to the complexity of the problem. Appreciable would mean in excess of a few percent I'd say. Thanks.

Khajidha... of course. Then again, it's just a thought exercise (a WP:RD exercise if you will).

Thanks friends --Ouro (blah blah) 19:13, 3 November 2022 (UTC)[reply]

Right-o - it's just that it's hard to say confidently whether we're looking at differences in - let's just pick one quantifiable parameter, cooling rate - of a few parts per hundred, or a few parts per million. It's hard to know - confidently - whether we can safely ignore some effects!

The beauty, and the curse, of the mathematics that model convective heat transfer is that they are highly sensitive (in the mathematical sense of that word). Small changes can be amplified by physical processes that are governed by nonlinear equations.

It is no coincidence that heat transfer is studied as a part of statistical physics. It is also no coincidence that convective heat transfer relates strongly to turbulent flow.

Your thought-experiment is a great one - but to really do it justice, we do need to start with much simpler thought-experiments. By this, I mean that we have to spend a pretty significant amount of study before we can come to any conclusion, if we care about a scientifically valid answer - let alone one that is accurate and precise enough to say "yeah, that's an effect whose size is, say, 3% to 5%."

Otherwise, we're kind of just not doing science - we're just guessing.

There is a lot of stuff in our universe - basically, the entire set of topics that we call experimental physics - where we can perform a controlled experiment more easily than we can answer from a theoretical perspective. But, a true experimental physicist cares about controlling the experiment so that they can draw some kind of generalizable conclusion. This is exactly how we end up with thousand-page textbooks where we can say, "hm, for a rack made out of an array of rods, use Equation 9.34 from the chapter on Free Convection." I mean, a correct answer does exist - a correct answer can exist - and that's what separates real physicists from postmodernist nihilists. We (physicists) subscribe to a world-view in which we believe we can find out truth and assign a number to it. They (post-modernist nihilists) tell us that truth defies understanding, let alone quantification.

"Neither of these world-views is more correct," say the post-modernist nihilists.

"Post-modern nihilists are in no position to tell us about correctness," retort the physicists.

Only... the experimental physicist has the fortitude of moral character, nay, the intellectual resolve, to spend thousands of hours slogging through the work to prove the philosophers are wrong.

So, uhm, ... let's get crackin' on that!

Nimur (talk) 21:11, 3 November 2022 (UTC)[reply]

Yes, waving them around will increase the rate of cooling. That's because as well as radiative and convective heat loss you also get conductive heat loss into cooler gas. That's why car radiators have fans. Greglocock (talk) 21:45, 3 November 2022 (UTC)[reply]

Car radiators use the simplifying assumption that the gas outside the engine cowling will be cooler, so they use a fan to impel cool gas across the radiator. Ambient air outside can be approximated as an infinite cold reservoir. So, it is thermodynamically efficient for the engine to spend a few extra joules (... which needs energy, which means burning more fuel, which adds extra heat), and then convert this surplus heat energy into kinetic energy in the fan, and we assert that the fan shall impel cold air toward the radiator, improving net efficiency during normal operation in normal, specified conditions.

Fans, like all non-perpetual motion machines, need energy to spin - and in this case, the energy comes from the engine, and so ... amazingly, adding the fan to the automobile engine causes heat to be added to the universe. It only so happens that the automobile engine is designed to put this heat "somewhere else". Somebody, (an engineer, perhaps) had to study those horrible airflow and convection equations to make sure this actually has a net cooling effect on the portion of the machine we care about! Does the fan actually cool the engine if... the outside air temperature is in Flagstaff, Arizona, in the summer, while driving 400 kilograms of astrophysicists up a steep hill, or is this contrived situation a case of inversion in parameters, in which the existence of this cooling-fan actually adds heat to the radiator?

What about other scenarios - where the normal operation of the system does not necessarily rely on forced air cooling? What if we designed for maximum efficiency with passive cooling - a fan would move us away from maximum efficiency!

Would a cooling fan be of any assistance in, say, an airplane engine? ...Or a coal-fired powerplant turbine? Would it cool the metal any faster if the "oven" were an iron smelter? How about a blast furnace (where cold air is added to increase the net temperature)? How about a sports car with a turbocharger, where cold air is blown at the engine intake by a fan? It really, really matters where the fan is and where the air goes - turbocharging an engine usually makes it get hotter, because cold air does more than convect - it can combust!

How about if the "cylindrical metal tube" is radiating into a cooling fluid that radiates into the vacuum of space (... or is exposed to direct sunlight in the vacuum of space), fluctuating between 4 and 280 kelvins, depending on the time of the month? How many billions of dollars does it cost if a simplified assumption flips the sign of the cooling rate, and what is the impact to weather forecasting for half a planet for the next two decades?

The scenarios are diverse, and in this diversity, the magnitude of the rate of cooling changes dramatically. In fact, even the sign of the value changes. So, it's never so simple unless we know what the scenario is doing!

Nimur (talk) 16:10, 4 November 2022 (UTC)[reply]

"What if we designed for maximum efficiency with passive cooling" For interest, this is exactly the case for Formula One (and other) racing car engines, which is why, when they return to their pits, team personnel have to direct externally driven cooling fans into their air intake ducts. {The poster formerly known as 87.81.230.195} 5.64.163.219 (talk) 08:15, 5 November 2022 (UTC)[reply]

In the case of practical engines, and particularly turbines, cooling is not just part of the Carnot cycle, but is also for engineering purposes. Differential expansion and contraction modified the clearances and if the oil gets too hot it looses its lubricating properties. Martin of Sheffield (talk) 08:24, 5 November 2022 (UTC)[reply]

A steadily held hot rod mainly cools by transferring heat to the surrounding air. Since the rate of heat flow is proportional to the difference in temperature between the rod and the air, the heat flow will thereby decrease and the cooling slows down more than necessary. This can be avoided by replacing the warm air continually by fresh cold air. One way of accomplishing this is by aiming a ventilator at the rod. Another way is swinging the rod through the air. Shaking it will mainly have an effect if the absolute displacement is considerable. --Lambiam 21:43, 3 November 2022 (UTC)[reply]

Just to add another important perspective here, and add on a bit to the excellent (though a bit TLDR) responses by Nimur above; when you wave the rack through the air, you're basically trying to take advantage of convection to the heat transfer situation. We can confidently say yes to the notion that it will cool off faster. The devil is in the details, however; if it cools an extra 0.01 kelvin per hour, that's hardly worth the effort spent doing it. The problem is that fluid dynamics is a famously impenetrable science to work in theoretically. You would need something akin to Newton's laws of motion and the work equation and the law of conservation of energy and the like for fluids (rather than objects). For objects, these are simple three-variable equations that any middle schooler can solve. For fluids, we've got the equations, its just that no one can solve them. No really, the fluid equivalent of all of the dynamics and kinematics equations you learned in high school physics are called the Navier–Stokes equations; actually solving them in three dimensions represents one of the Millennium Prize Problems, which tells you they are still unsolved. The issue is that Navier-Stokes doesn't play well with turbulence, and that's why we have the Navier–Stokes existence and smoothness problem. Since solving "how much energy is carried away by convection" requires us to accurately model fluid dynamics around your waving oven grid, and that flow will be turbulent, not only do we not have solutions for such a model; we don't even know whether or not they exist. --Jayron 32 12:30, 4 November 2022 (UTC)[reply]
I'll work on brevity, (but not today)! Nimur (talk) 16:11, 4 November 2022 (UTC)[reply]

I got my brevity down pat, Nimur, but you forget it if you do such excellent work. I am reading through your answers, friends, and thanks. Of course we could have (should have) started off much simpler, with say - one rod (one wire) that is shaken or not and then to measure the heat transfer away from the object... and then somehow transpose that (with all the details like material, make-up, design details, etc.) and work upwards towards the oven rack. And Jayron you're absolutely spot on about fluid dynamics being difficult - I know. Thanks anyway, you got me a lot to think about. --Ouro (blah blah) 18:18, 4 November 2022 (UTC)[reply]

One thing that is still true; you can work this stuff out empirically. You can shake rods of different thicknesses at different speeds in different environments, you can plot the results on graphs and interpolate and extrapolate the data to develop models of cooling that don't depend on knowing anything about fluid dynamics. Newton himself developed Newton's law of cooling using carefully controlled experiments. However, the problem is that you can't work from first principles to develop a theory of cooling that would work here, in the same way that we have good theories explaining things like balls rolling down hills and hockey pucks colliding on ice. Even though the same principles apply to describe colliding hockey pucks and cooling off waving chunks of metal in the air, the math is just too intractable using the tools we have today to do so. --Jayron 32 18:37, 4 November 2022 (UTC)[reply]

But what is the sound of one hand shaking? (My Zen master suggests that this question may not even exist.) MinorProphet (talk) 01:31, 10 November 2022 (UTC)[reply]

Kem Kem Leptocleidid.

When is the new leptocleidid plesiosaur from the Kem Kem going to be given a name? CuddleKing1993 (talk) 21:27, 3 November 2022 (UTC)[reply]

If you mean a binomial name, it is not so simple as naming a new-born baby. The first issue is the assignment of a genus. Do all fossils from this group belong to the same genus? And if so, is it one of the known genera, or a new one? Such questions require careful study. If this can be resolved, the questions repeat at the species level. --Lambiam 22:12, 3 November 2022 (UTC)[reply]

The ICZN, International Commission on Zoological Nomenclature, maintains the process for assigning binomial names; they don't name the organisms themselves but they do set the standards for how things are supposed to be named, and they do adjudicate disputes. The process is described in a document called the International Code of Zoological Nomenclature (also abbreviated ICZN). The process of granting the name does take time, so it's hard to predict "when" such a name will be published. It depends a bit both on the discoverer of the species (who has the right to name it) and to the publisher of the work in which it is named. As Lambiam notes above, what needs to be done first is to figure out what the taxonomy/cladistics of the species is; such as to which genus it should belong, or does it represent a new genus; should it be a species on its own, or a subspecies, to which family should it belong, and so on up the line. That kind of determination takes real labor and work on the part of scientists who need to look at the fossils, analyze them, and come to conclusions. --Jayron 32 12:16, 4 November 2022 (UTC)[reply]

In the past discoverers would name specimens without taking such careful precautions. But this led to many cases of multiple names being given to what turned out to be the same thing. Which meant standards had to be set up for which name was to be used going forward. Usually strict priority is the determining factor, but there have been exceptions that were explicitly made for good reasons (if the oldest name was never used after its initial publication and a later name was used in numerous publications, it would be counterproductive to insist on strict priority). --User:Khajidha (talk) (contributions) 13:41, 4 November 2022 (UTC)[reply]