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Q & A: Heating Fast, Heating Slow

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Most recent answer: 10/22/2007
Q:
Under what circumstances will ice, at -20 degrees, reach 100 degrees faster than water at 60 degrees when the room temperature is 20 degrees? Why?
- Neil
A:
Neil -

Unless you've got some sort of heating system, then what you're suggesting is impossible. Objects will heat up or cool down until they reach the same temperature as they're environment... So a -20 degree ice cube in a 20 degree room will heat up only to 20 degrees, then stop. Similarly, the 60 degree water will cool down until it reaches 20 degrees, then stop. Unless you have a heater like a stove to set them on, there's no way for either to reach 100 degrees.

At first glance, I read your question wrong and figured you were talking about heating things up in a room where the air was hotter than you wanted the ice/water to become - say 200 degrees. (Ok, this is really hot, but if you're talking about setting them both on a gas stove, not too unreal.) Rather than delete it, I figured I'd post my original answer too.

-Tamara

If the air temperature was 200 degrees:

The important here is not how much hotter the room is than the
ice/water, but how quickly the ice/water heats up. Sure, the
temperature of the room is important, but that's not all there is.
In order for the ice/water to heat up, heat needs to move from the
air into the ice/water. So if you want the ice to reach 60 degrees
first, then you need to either (a) make heat go into the ice cube
faster or (b) make heat go into the water more slowly. There's a
LOT of ways that this can happen, but here's a couple of examples:

(a) Making heat go from the air to the ice cube faster. One way to
do this is to make sure the air around the ice cube keeps moving.
As the ice cube warms up, the air near it cools down. So you'll
want fresh warm air to move in and take its place.

(b) Making heat go from the air into the water more slowly. One
possibility is to put the water in a
href="http://van.hep.uiuc.edu/van/qa/section/States_of_Matter_and_EnergyTemperature_and_Heat/948650236.htm">Thermos
.

Like I said, there's a lot of ways this can be done. Use your
imagination!

For more information on how heat is transfered, look .

(published on 10/22/2007)

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