Can warm water freeze faster than cold water?
Surprisingly, yes it can. Warm water can freeze faster than cold water, provided the proper conditions are in place. When it does happen it is known as the Mpemba Effect.
To demonstrate it yourself you will need two identical containers of the same size and shape and access to warm and cold water.
1. Fill each container with the same amount of water, but make sure that the initial temperature of the water in each container is slightly different - starting temperatures of 70 degrees centigrade and 30 degrees centigrade, respectively, work well.
2. Put both containers in the freezer.
3. As the water in the containers cools, you will find that the container with the warmer water (70 degrees) will freeze faster than the container with the cooler water (at 30 degrees).
This defies immediate logic and even scientists are not in agreement about exactly how it happens. The main factors that are broadly agreed on are that freezing the hotter water affects its scientific properties e.g. some of it evaporates so there is less to freeze, the way heat moves through it changes, the gases in it change, it affects its surroundings in the freezer and also experiences a phenomenon called supercooling, which means that it can freeze at a slightly higher temperature than colder water.
For such an everyday substance, water is surprisingly complex and there are a number of ways in which it does not behave as expected. Happily, this leads to there being at least one 'myth' about it that in fact be proven true!
Other experiments:
|
