I’ve done a very carefully controlled, highly scientific experiment in my kitchen. I put two quarts of warm water into a pot, and two quarts of cold water into another pot of identical dimensions. Then I turned on the stove, to the same flame height under both pots. The hot water came to a boil at the same time as the cold.
Why wasn’t it faster, given that the warm water was already partway to boiling and thus had a head start when I turned them both on?
Had the warm water been previously boiled, then allowed to cool?
Here’s Cecil’s answer to your question.
How warm was the warm water? How cold was the cold? Were the pots identical, or just of identical dimensions? If the pots are made of different materials, then that might affect your findings.
I suspect your experiment wasn’t carefully controlled enough. “Flame of the same height” doesn’t cut it when you’re trying push the boundaries of science outward.
The problem is probably that the rate at which the burner heats the water is rapid enough so that the warm water didn’t have enough of a head start, so to speak, to be perceptible within the limits of error of your experiment. For example, “coming to a boil at the same time” isn’t very precise – there’s no one point at which a pot of water can be said to have come to a boil, as you tend to start with little bubbles eventually becoming bigger until you get a full rolling boil. An accurate thermometer would be more useful in judging when boiling temperature has been reached.
How many times did you replicate your experiment?
One thing you need to realize is that most of the time waiting for the water to boil consists of raising the temperature by zero degrees. For 1 gram of water, it takes 50 calories to raise it’s temperature from 50C to 100C, and then another 539 calories to cause it to boil. So, the difference between starting with warm water and cold water is small to begin with, and is being swamped in your measurement error.
The 539 calories apply if all the water is turned into steam. so the difference for a pot of water “brought to a boil” is much smaller. But the measurement errors would indeed be large here, and the experiment should be repeated a few times, alternating which burner is used for hot and which for cold.
Alternating post would be good, too.
It took me a while, but I belive BigT here meant alternating pots, which I agree with.
Thermometers could improve the quality of your data.
The warm water had not been boiled before. The cold was from the cold tap only and was maybe 40*F, the warm was a little warmer than body temp. So there was a difference between them of about 50 or 60 degrees. Not scientifically measured, but what appeared to me to be a significant difference in temp.
No, I didn’t use a thermometer - it wasn’t that scientific. It’s just something that I’ve noticed over time, and wanted to try. I cook a lot and brought both pots to a full rolling boil. The small bubbles appeared at pretty much the same time, as did the full boil.
The pots were both 5-ply stainless.
You probably introduced some experimenter bias as well as the others already mentioned. If 10 people each said “Now!” when the boil started, but didn’t know when the other 9 said it, it’s unlikely they would be a simultaneous chorus. That’s why a thermometer is a good idea.
I applaud your efforts, but I can’t say it was that.
So maybe there’s room for improvement between “highly scientific” and “not that scientific”?
I was being facetious…
When? When you said the experiment was highly scientific or when you said you didn’t use a thermometer?
This Forum is General Questions, where a question is expected to have a factual answer (not that some tomfoolery isn’t expected to liven up the discussion). If you don’t have a serious question, maybe one of the lighter fora would be more appropriate?
Frankly, I wonder a little bit about both of those temperature estimates. 40F water is COLD. I’d say room temp or slightly below is more likely: lets say 60F. [If you do have 40*F tap water, you shouldn’t be worried about boiling times; you should be worried about how to stop your pipes from freezing and bursting in this dreadful cold snap you’re having].
And for water that feels ‘warm’ I think that’s probably not body temperature but skin temperature (I think most people would describe 100F water as ‘Hot’.), so let’s say 80F (warmer than room temperature, but not hot).
So now we’re looking at going from 60 to 212 versus going from 80 to 212, or a jump of (to the nearest ten) 150 versus 130. That’s going to look pretty much the same, without very careful timing.
Were you watching either pot? Cause that will screw up your esperiment.
In general, if the difference between your initial conditions is smaller than the error of your measurements, you will not detect a difference in outcomes.
In your experiment, you used qualitative measurements, which have large inherent errors. Also, as others said, there may have been other confounders, like differeces between the heating temperatures of each pot, etc.
Assuming that the confounders were minimal, what you may have found is that the error in your qualitative assessment of when the pots “boiled” is larger than the error in your qualitative assessment of the difference in initial temperatures between the two pots. In other words, you are better at judging temperaure by touch than boiling by sight.
Now, that’s interesting.
use absolutely identical pans or a single pan, equilibrated to the starting water temperature. tap water will be about 60F at its coldest. warm feeling water will be near 100F. a metal pan at room temperature will affect the temperature of either type of water put into it.
the thermometer needs to be placed not touching the pan and in about the same position (in the middle of the water volume is best) each time.
do at least three trials.
that would be moderate quality scientific experiment in your kitchen.
Well, I just tried it.
Two iterations, two identical brands and types of pots, warm and cold tap water, no lids. Switched pots and burners on the second run. (note: cooled both pots with tepid tap water on the second run.)
Both times the warm began to get bubbles nearly thirty seconds before the cold, began to have rising bubbles about five seconds earlier.
Tris
Jeez, relax. I’m sure the Penguin does want a factual answer to her question, but was being facetious when she said her experiement was “very carefully controlled [and] highly scientific.”
When I make coffee in my percolator, and I’m in a hurry, I leave the flame cranked high til it starts perking, then turn it down so it doesn’t boil over. The Perk sound is distinctive and not at all subjective, so it makes a good “scientific” finish point. I have to stand there watching it before turning it down about 2 or 3 minutes less when I fill it with hot tap water vs cold. That’s with full hot, though, not “warm”. Call it 120 f vs 55 f.
Penguinlady’s experiment shows more scientific rigour than an episode of Mythbusters; her methodology is sound, she just lacks the necessary apparatus. Besides, the first sentence of the OP is written in the font Monotype Ironic Heavy Sans, always a clue.
It’s a popular myth that filling a kettle from the hot tap will save lots of energy, as evidenced from the various numptys where I work that do it. Thoughtfully, they will fill the kettle to the top for their one little cup so that many others after them will get to enjoy the taste of dead-pigeon-floating-in-a-loft-tank, with just a soupcon of Legionnaires Disease. The proper way to explain this is one cockpunch per syllable, but even so some people don’t get the message, and cite the filthy bastards mantra “what doesn’t kill you makes you stronger”. Great, you’ll get some benefit from that savage cockpunching then.
If you want to use less energy, only boil what you need as and when you need it. Besides, even if it’s from a decent source, re-boiled water makes a rank cup of tea (it’s the dissolved oxygen again, a decent infusion of tea needs it, even if it does extend the boiling time slightly). And think of that dead pigeon if you’re ever tempted to drink from the hot tap.