Lessons from Prince Rupert’s Drop

As an old physics teacher, I always had a few “tricks” up my sleeve to throw at my students when they looked like they might be dozing off. Here is one that was usually a part of our studies of kinetics and the laws of solids, liquids, and gases. Prince Rupert’s drops are glass tear-drop shaped beads with a tail. In Hawaii, these drops occur naturally and are called Pele’s tears in honor of the volcano goddess Pele. My students learned lessons from Prince Rupert’s drop, and perhaps you can too.

In 1660 Prince Rupert of the Rhine introduced the drops to English scientists. The drops are made by quickly dripping very hot glass into water. As the glass cools, it becomes hard and clear. The bead part can withstand 3400 pounds (15,000 Newtons) of force. You can hit it with a hammer and it won’t break. The tail of the drop is very thin, and you can easily break it. The result is that the entire bead violently explodes into millions of dust-sized fragments.

If a student were dozing off, I would do my old “A or F” trick. I would tell the student if they could break the tail off the glass bead they would get an A, but if they broke the bead or scratched it in any way they would get an F. With the class watching, the student would carefully break off the tip, and to their surprise, the tear-drop would explode. Then the rest of the students would want to try it, leading to lessons from Prince Rupert’s drop.

The physics behind this is fascinating. The glass behaves as a liquid according to Pascal’s Law, which says, “Pressure exerted on a fluid is distributed uniformly throughout the fluid.” Because the tail has a very small diameter, the pressure exerted on the tail is beyond the tensile strength of the glass. The modulus graph for this material is very strange, with the glass not bending or stretching and thus having no elastic limit. We can see glass behaving as a liquid in other cases. Windows in old houses tend to flow so that the windowpane is thicker at the bottom than at the top. Scientists have learned lessons from Prince Rupert’s drop that gave us toughened glass for the screens in today’s phones and tablets.

We can also learn some lessons from Prince Rupert’s drop. One is that things are not always what they appear to be. The drops are beautiful. Shining a laser into them produces interesting light patterns. The bulb of the drop seems to be indestructible, but a small change in the tail produces wholesale destruction in the entire thing. What was once a beautiful tear-shaped drop of glass is now a pile of powder.

The moral challenges that we all face are very much the same. Things are not always what they appear to be. Something beautiful can become an ugly pile of dust if it has even a single break in any part of it. Sex is beautiful and used as it was designed to be, it can bring great joy and love. One misuse of it can turn a life into an ugly thing that can’t be put back together by any physical process. Only the healing that Christ brings can restore the beauty of a broken sexual relationship.

— John N. Clayton © 2020

You can see a video demonstration of Prince Rupert’s drops by clicking HERE.