 This is a question that many people wonder about. You may have heard people say that hot water will freeze faster than cold water, and perhaps you wondered if this were true, and how it could be possible. Well, we decided to find out ... on this page we'll show you an experiment we did, and explain what really happens and why. 
 Our experiment was a very simple one. On a cold day, we left two identical shallow pans outside to get cold. The temperature outside was -21°C. Then we prepared two 300 ml samples of tap water. One was cold, at a temperature of 19°C. The other one we heated in a microwave oven to the boiling point, 100°C. We carefully poured each of the samples into the two pans, and recorded how long it took for the water in each pan to freeze. We found that after approximately 4 minutes, the cold water began to freeze, and was mostly frozen within another minute. The hot water showed no sign of freezing at all. Our conclusion at this point might be that cold water freezes faster than hot water. This would seem to make sense, since the temperature has less far to drop from 19°C to 0°C than it does from near 100°C to 0°C. However, this isn't the whole story. People have known for hundreds of years that, under certain circumstances, water that is very hot will freeze faster than cold water. The classic example describes water left outdoors in wooden buckets in winter, where one bucket contains hot water and will always freeze first. Can this be true? If so, why does it happen, and why didn't it happen when we did the experiment above? To find out, we did the experiment again. This time we used styrofoam cups, and put them in the freezer. The freezer temperature was -10°C, and we used 30 ml of water in both cups. One cup contained cold tap water at 19°C, and the other contained tap water heated to 100°C in a microwave. You'll notice we changed the conditions for this experiment ... different locations, amounts, containers, and temperatures. One of these changes was significant ... can you guess which one? Go on to page two to find out, and see which one froze first. |