Physics question

Hi,

Probable more a physics question then rec.puzzles - but I know people know things in here...

Why is it intrinsically more difficult to cool things down. There are loads of ways to heat things up, some more quickly than others (I have a microwave in mind) - but why can't someone come up with a similar way to cool things down?

Particularly in the kitchen?

Cheers.

OK - I'll try. Reasonably informed lay opinion follows...

To heat something up, you add thermal energy. That's easy to do. To cool it down, you have to somehow 'leach' the thermal energy back out of it - give it some other object which it will heat up. But it's hard to get the energy *out* of the substance because it's distributed through it.

It's worth noting that heating something up *evenly* is *not* an easy thing to do - we have to stir liquids to move the molecules around so they get a uniform application of energy. Microwaves are an exception, but there's no way to microwave something 'in reverse' unless you can get it to somehow emit microwaves from itself. Otherwise, you have to gradually heat the substance up in a conventional oven using an ambient temperature, just as you do with cooling things down.

You *could* use alternative cooling methods to cool things down. A blast of dry ice, for example, would have a similar cooling effect to the heating effect of steaming something, so you could probably cool a cake with it. Similarly, if you blasted cooled nitrogen on the base of a pan, it would have a similar cooling effect to the heating effect of a flame. But these aren't really practical uses in the kitchen!

One last point is that you can get a much higher temperature gradient when heating things up because there's no real limit to how hot you can make the flame (because once something's boiling, it doesn't get any hotter until it's dry). When cooling, you don't want to cool below the temperature where your food will degrade, which limits your cooling temperature.

Kevin Stone performed an arpeggio on a keyboard and produced:

Almost the exact same question was asked on the SDMB about a week ago:
http://boards.straightdope.com/sdmb/showthread.php?& threadid=1319

You are, of course,taking a view that is localized both in space and time but is unspecified. You could change any answer by altering the frame of reference. That means the question is meaningless without a frame of referrence. No matter what you do to warm something up I can demonstrate that it will cool off by extending the time frame. No matter what you do to cool something off I can warm it by relocating it in space.

The universe has been cooling since the beginning, never warming. This is caused by the expansion of a universe with a constant sum of mass/energy.

If the universe is balanced or open, the cooling continues forever. If the universe is closed, the cooling will eventually be followed by warming. If the universe is cyclic the cooling/warming cycles will repeat.

Individual atomic nucleii might have a constant temperature over extremely long time frames. However, if it turns out that the proton does decay then even the most stable nuclear structures will eventually cool down.

The reason things appear intrinsically more difficult to cool in the kitchen in human time frames is the fact that we are constantly being exposed to solar radiation. This quality is a localized artefact. Eliminate all manmade sources of heat and just wait for the seasons to change. You'll observe a repeating cycle of cooling and warming. You'll find that overall, things are at thermal equilibrium with the solar flux and have no intrinsic quality to be either warmer or cooler than the environment.

Radioactives may feel warmer than their environment but are actually cooing down over time and will eventually achieve thermal equilibrium.

Hi,

I agree with what you say, but this doesn't really answer my question though?

Essentially, it's because just about any sort of energy which you just arbitrarily dump into something will ultimately turn into 'waste' heat, and no matter what you do, you'll generate some amount of waste heat.

When heating something up, any sort of inefficiency in the process turns into waste heat

Lots of good answers I read with interest and curiosity. The one big exception to your general observation occurs to me as I drive off to work on a cold winter day in Rochester. Why is it easy to cool the interior of the car quickly in summer but it takes so damn long to have any heat in the winter? I understand the mechanics and

Isaac Kuo:

That may be...

...but this is false. Try a web search on 'residential heat pumps'.

John Bailey:

It isn't, really. It's easy to produce a small amount of cool air to blow on you. Try sitting in the back sometime and see how fast it cools.

That's the answer. Because the heat *is* a by-product, you don't get any until the engine warms up. Perhaps in a luxury car supplementary electric heating could be provided to give warm air quicker, but most people wouldn't want to pay for an electric heater that would only be used for a few minutes a day, nor for the fuel to carry it around.

Correct me if I'm wrong, please, but don't these heat pumps always go 'with' the natural hot->cold grain? In other words, they pump heat from warm ground (or water or whatever) to heat up the cooler house in the winter.

Isaac Kuo

There is, but my test subjects died from carbon monoxide poisoning when I routed the exhaust pipe into the heater ducts.