Lickszz Posted September 9, 2003 Share Posted September 9, 2003 I've been having a discussion with a friend and I'd like peoples thoughts/answers on the following: If 2 buckets of water are placed in a location where the ambient temperature is the same (enough to freeze water) which bucket will freeze first, a bucket of cold water or a bucket of warm water? My friend believes that the bucket of warm water will freeze first. This is because there is a greater heat loss from the warm water and so the temperature falls quicker, thereby freezing quicker. I on the other hand believe the bucket of cold water will freeze first because the warm water may cool quicker at first but will then after a couple of minutes follow the same cooling curve thereafter. The cold water will still have been cooling also so would freeze first. I am not sure if this would vary if the size of water containers was bigger or smaller. What do you think? Link to comment Share on other sites More sharing options...
Andy Posted September 9, 2003 Share Posted September 9, 2003 I think you're right. The size would only make a difference if the two containers were differnt sizes. Otherwise, it wouldn't matter whether they were ice cube makers or wheelie-bins. Link to comment Share on other sites More sharing options...
max Posted September 9, 2003 Share Posted September 9, 2003 It's after 10 at night and you're posing physics problems. Thanks a bunch. fwiw, imho, the cold one would freeze first, or they would freeze together. If the warm one does cool more quickly then, at some point, it would attain the same temp as the other and they would then cool at the same rate together. Link to comment Share on other sites More sharing options...
Cycleracer Posted September 9, 2003 Share Posted September 9, 2003 Why don't you test this theory yourself by placing a cup of cold water in your freezer along with a warm cup of water and see which freezes first. Link to comment Share on other sites More sharing options...
scaramanga Posted September 10, 2003 Share Posted September 10, 2003 Ill go for the cold. So your friend is saying the hotter the faster something cools? Hmmm... So a semi frozen bucket of water would freeze after a bucket of near boiling water? Dosent sound right to me. Link to comment Share on other sites More sharing options...
John Posted September 10, 2003 Share Posted September 10, 2003 The cold water will freeze faster than warm water. However, it is possible for boiling hot water to freeze faster than hot water. Why? Water gives off steam therefore the amount of water to freeze would be less and therefore it cool and freezes faster. I'm not sure what tempatures are require to make this condition work - probably higher than boiling point. Link to comment Share on other sites More sharing options...
RPG Posted September 10, 2003 Share Posted September 10, 2003 a luke warm cup of water will freeze faster (and cleaner) than a room temperature cup of water Link to comment Share on other sites More sharing options...
Lickszz Posted September 10, 2003 Author Share Posted September 10, 2003 Originally posted by scaramanga Ill go for the cold. So your friend is saying the hotter the faster something cools? Hmmm... So a semi frozen bucket of water would freeze after a bucket of near boiling water? Dosent sound right to me. Not semi frozen. Just cold water and warm water. My friend agrees that with small volumes of water, as in an icecube tray, the cold water will freeze first. However, their reasoning with a much larger volume, as in the case of a typical bucket. As the warm (I emphasise WARM, probably around 100F or 38C) water cools in contact with the air and the inner surface of the bucket, it tends to sink towards the bottom, being denser. This results in convection currents, downwards near the inner surface of the bucket, and upwards in the centre. These currents continue, although slowing down as the water cools, resulting in a more efficient transfer of heat through the bucket, and from the surface of the water, to the colder air. My friend claims this has been demonstrated by experiment, with the observation that the originally warm water freezes from the sides and base of the bucket inwards. The cold water, on the other hand, freezes initially on its surface, as water at 4C (maximum density) will have slowly sunk to the bottom of the bucket, and water at < 4C rises to the top. My friend is a Science teacher, so who am I to argue? Link to comment Share on other sites More sharing options...
Lickszz Posted September 10, 2003 Author Share Posted September 10, 2003 Originally posted by The Cycleracer Why don't you test this theory yourself by placing a cup of cold water in your freezer along with a warm cup of water and see which freezes first. I have already tried it. Here is my reasonings and findings why I am convinced the cold water would freeze first. I agree that it is true that the hot sample will initially lose heat at a faster rate than the cool sample, which can offset the obvious fact that it has to become cool before it freezes, but in the case of buckets full of water, this would only happen in a near vacuum. The hot water could only possibly freeze first in more normal circumstances IMO when the ambient temperature is much lower than either sample and the samples have a high surface area: volume ratio. For example, an ordinary ice-cube tray filled with cold tap water froze solid in my freezer compartment in less than a fifth of the time taken for the same tray filled with recently boiled water to freeze. (I opened the door every minute to check progress, which obviously tainted the results, but I suggest a time difference of 500% is fairly conclusive). When the tray was only half filled, the time difference was about 400%, a quarter filled, 100%. When I just barely covered the bottom of the tray with water, in both cases the sample had frozen the first time I checked. From my results, I conclude by extrapolation that a bucket full of hot water, having a much lower surface: volume ratio than an ice cube tray, would have taken many many times longer to freeze than a bucket of cold. I cannot claim direct proof of this hypothesis since my bucket won't fit in my freezer compartment. Link to comment Share on other sites More sharing options...
halevan Posted September 10, 2003 Share Posted September 10, 2003 The warm water will freeze first, strange as it may seem. Link to comment Share on other sites More sharing options...
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