Even in death, this teacher enlightens

The news arrived as such news usually does — through an official e-mail from the school. It was quickly confirmed on social media — an old physics and chemistry teacher had died.

I read his obituary with genuine sadness. Then, an odd comment caught my attention. The obituary mentioned that the deceased used to show his physics students a spot in Stearns County, Minn., where a car could roll uphill.

I thought to myself, "What? He never showed our class that spot!" After a moment I thought, "I need to find that spot so I can understand the science behind it!"

I then paused and marveled further. Even from his grave, my old teacher, Pete Froehle, was still piquing my curiosity.

A favorite Froehle lesson came to mind. The prep school I attended is located in central Minnesota and in January it was not uncommon for the school day to start with the temperature hovering near 20 degrees below zero Fahrenheit (minus 29 degrees Celsius).

One day my senior year, Mr. Froehle asked his chemistry students which would freeze first — cold water or boiling hot water.

"What a stupid question," I remember thinking. The answer is obvious — cold water will freeze first because it is closer to zero degrees (Celsius) — the temperature at which water freezes.

Mr. Froehle then asked us to conduct our own experiment. I recall heating some water on a beaker to boiling point and then placing equal amounts of cold and boiling hot water in separate containers and placing both outside the door of Mr. Froehle's first-floor classroom into the subzero morning temperatures. Alas, the bell rang before the experiment was completed.

I was one of the fortunate few to have study hall immediately after the class and was thus able to monitor the experiment. After about 15 minutes in the freezing temperatures, I was stunned to discover that the boiling water was turning to ice first.

If memory serves, Mr. Froehle never returned to the science behind the counterintuitive effect but a few years ago I recalled the experiment and went to the internet to better understand the phenomenon. I learned this apparent quirk of nature is known as the "Mpemba effect" and is named after the Tanzanian high school student, Erasto Mpemba, who first observed it in 1963.

Ironically, after I learned of my old teacher's death, the temperature in my hometown of Minneapolis was a minus 10 Fahrenheit. For old times' sake, I reran the experiment I had first conducted 40 years earlier.

The results were different! The cold water froze first this time. Employing the scientific method, I conducted the experiment a second time. Again, the results showed the cold water freezing first.

It turns out that hot water can freeze before cooler water only under certain conditions.

I could explain to you why this is the case. But then I wouldn't be a very good teacher, would I? The best way to learn is to conduct experiments yourself, and when the results are either counterintuitive or not consistent, the key is to stay curious.

Pete Froehle was a great teacher. He was extraordinary not because he gave his students all the answers but because he encouraged us to have an open mind and keep asking questions.

I could tell you more about Pete Froehle but I have to go. I have a spot to find in Stearns County where a car can roll uphill.

Jack Uldrich lives in Minneapolis.