Please answer a simple science question

Mine was shorter.

(Where have I heard that before?)

I like Drew's statement, "Since the cooler water will be slightly more dense, it will therefore require slightly more energy to be transfered, which will take slightly longer."

Since this thread started I have conducted a simple experiment. First I set the room thermostat at exactlty 70f. (I have a very sensitive and accurate central heating system).

Then I heated 1 pint of water to just over 75f on the stove.

Then I put one pint of water in the fridge for a few minutes.

Both pints had thermometers in them.

Then I put both pints of water on the kitchen table and with seperate stop watches started timing when each water passed respectively 65f and 75f. Then I timed each volume of water as it heated or cooled to 70f. And the result clearly shows......cont.

The rate of heat transfer is proportional to the surface area available for heat tranfer and the difference in temperature between the water and the room. The amount of energy required is the temperature change times the mass of water times the heat capacity of the water. If your containers are identical and filled with the same volume of liquid, then the initial rate of heat transfer is the same since the area and surface areas are the same. Next comes the mass. The mass of cold water in a given volume is SLIGHTLY denser than the warm water, so it requires SLIGHTLY more energy to warm up the cold water because there is more of it.

So, it takes a very small amount of extra time to warm up the cold water compared to cooling the warm water. It is so small, it is probably not measurable with a kitchen thermometer. I would call it a draw.

Bloody Hell chaps (notice there were no 'chapesess'), I feel another gender topic coming on)

Thanks so much for all your replies!

The fish is back and happy home now. :wink:

Jesus friggin' Cripes! I've been sitting at my kitchen table for the last five hours trying to come up with an answer for this question. I filled two glasses with water from the tap. Then I added cold to one and hot to the other. I nursed a beer as I watched the glasses for five minutes. Then I stuck my finger in each one. I couldn't tell a damn thing, so I took my gloves off and tried again. Nothing. No discernible difference.

I've always prided myself on being very scientific and coming up with logical answers, but I am stumped by this one.

In my scientific gut (yeah right) I've a feeling that warm water cools quicker than cold water warms - but don't know why?

Gus, your not supposed to measure the temp of water with your fingers, your supposed to use a more sensitive area of your body...your elbow!

Glad you picked up on some of the replies smorgs. There's been an awful lot of messing around with tepid water here, pity if it was to go to waste.

As I believe your cover story a bit fishy, and what you really wanted to do was see the silly explanations on a2k, would you like to tell us the answer now that we are all awash?

I can spot a PhD from UMIST quite easily.

I came up with, 75 will reach 70 first. I considered the the two masses as being equal, the water and the size of the bowls, then I considered the air temp, which seemed to make a difference in my minds eye, (i don't have a degree in anything, btw, I can only describe the pictures in my head.)

I don't know how to explain,...it seemed like the room temp. had a greater/quicker effect on the warmer water.
Does it have something to do with the warm moist molecules/energy that were emitted in to the air, and the mass of molecules created a type of pull/chain reaction?

From a childs view point. I hope the true explanation isn't to difficult to understand, I shall wait.

smorgs, Actually the wrist is considered "sensitive" enough to tell the difference in temperature. I also guessed the warm water would cool faster than cold water warming too. I guess "smart" people think alike. LOL Me smart? ROLFLMAO

What about evaporation?
Evaporation consumes a huge amount of energy. You could easily make an argument that the warmer water sees more evaporation therefore cools down faster. If the hot water was very hot and the cold water was very cold, I think the hot water would cool more quickly than the cold water would heat up.

paulaj...sexy and clever, what a combination!

Your the only woman to reply on this thread...well done!


Still no difinitive answer though

Steve "the results clearly show" what?

UMIST (snicker)

I used to go to the Saturday night disco there in 1980...my only connection!

OK folks this is the best I can do.


If the room is perfectly thermally insulated, then neither bowl of water will ever reach 70 F. Heat only flows one way, so in one case the air warms the water, in the other the water warms the air. In the case of the cooler water, air at 70f warms it up a bit. But in giving up heat to the water, it must lose temperature itself. So both water and air end up at some temperature intermediate between 65 and 70. The water will NEVER get to 70f. [Unless heat comes into the room but thats not allowed if its perfectly insulated]

In the case of the warmer 75f water, heat flows into the air. But this will warm up the air slightly. Again both water and air will settle on an intermediate temperature this time between 70 and 75. [Probably only fractionally above 70] But it will never cool to 70f exactly unless heat is lost from the room and thats not possible if its insulated.

Ok I hear you say lets talk about real rooms with doors and windows etc. Here we are talking about heat transfer between a mass of water and very large mass of air. If a door is open you could take the air mass to be the whole atmosphere. Therefore it will not heat up or cool down by any significant amount by heat transfer to or from any bowl of water (unless said bowl is equivalent to pacific ocean). Therefore you have a delta t (initially) of 5 deg f across the air water boundary. The dominant heat transfer mode will be convection and evaporation, and I would suggest this rate of heat transfer would only be dependent on the DT, and not the direction (air to water or water to air). Thus assuming each bowl has equal surface area of water exposed, both the 65f water and the 75f water will take the same time to reach 70f.

Conversly the bowl of water with the bigger surface area (shallower/wider) will always get to 70f first regardless of it being warmer or colder.

Thats me done with tepid water.

Sheffield, eh? :wink:

Ah, exposure is one element that is very important to the study of temperature change.

Yes Sheffied University. Famous for its Department of Tepidology.

Did you do studies in Tepidarium? :wink:

Yes, I remember: they did some excellent works re. natural birthcontrol (symptothermale methode).

Francis, of course. As I was always getting into hot water at school.