# Here is a Theoretical Question I have been pondering

## Main Question or Discussion Point

Here it goes:

You purchase a cup of coffee at Dunkin Donuts. The coffee is about 90deg. in a styrofoam insulated cup. The main question is: Should you mix your cream, which is about 5deg cels, in the coffee at dunkin donuts or wait til you get home? The temperature outside is about 25deg. Home is about 5-10min away by car. It's not a trick question. Ok it should be that you mix the cream before, but why?

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mgb_phys
Homework Helper
Assuming the intention is to keep the coffee as hot as possible - milk later.
The cold milk will rise in temperature on the way home.
The rate of cooling of the coffee is proportional to temperature so cooler (milky) coffee would cool more slowly but at any point in the cooling curve it will be cooler if the milk is added.

LURCH
Also, the rate of heat loss by the coffee is slower not only due to the insulated cup, but the greater volume of the fluid, which makes a greater ratio of mass/surface area. The temperature change in the creamer will be more rapid because it is a smaller body.

But for me, the goal is to get the coffee cooled down enough to begin drinking sooner without burning my mouth, so I add and mix immediately.

Ranger Mike