Wednesday, July 16, 2008

Melting Ice in Coffee

I'm sponsoring a daily physics problem contest for the students. Today's is:

You have a cup of hot coffee and a small ice cube (which is in a freezer). Should you drop the ice cube in the coffee first, then wait for it to finish cooling enough to drink, or let it cool some first, then drop in the ice cube? (No, you cannot just put the coffee in the freezer).

(Answer to appear with tomorrow's problem).


Nikita said...

Let it cool a bit then drop in the ice cube.

kangway said...

I agree with Nikita, although I can't explain this well at the moment. Basically, the rate of cooling will be fairly fast at the beginning because of the temperature difference between the coffee and the room, so adding the ice cube will not affect the rate of cooling as dramatically as waiting for the coffee to cool, at which the rate of cooling slows, and then adding the ice cube.

Actually, I'm not entirely convinced my answer is right, but there we go.

Markkimarkkonnen said...

kway, answer now posted.

if you were to add cold milk instead of ice, the answer would be the same, but the difference between the methods would be less dramatic