Cold vs Hot Water Bucket: Which One Will Freeze First?

Run this experiment in cold weather.

Let me share with you a counterintuitive phenomenon.

Which water bucket will freeze first on a cold winter day: A cold water bucket or a hot water bucket?

Image from freepik

We may be tempted to say it is the cold water bucket. Our intuition assumes that the cooling process is controlled by a single quantity — temperature.

But this is only part of the picture. Consider the following:

• The initially warmer water develops a higher cooling rate due to the larger temperature difference with the surrounding environment.
• The initially warmer water evaporates more rapidly, which reduces its mass. Less water means faster cooling.
• The initially warmer water builds up a more non-uniform temperature distribution, which leads to convection currents. These currents remove heat from warmer regions more efficiently.

Result? The hot water bucket will freeze first.

This is called the Mpemba effect and observed for a wide range of experimental conditions.