Russell J. Composto

I bet you can recall at least one teacher who excited and engaged you in the subject matter, left you wanting to learn more, and quite possibly impacted your career choice. To me that teacher was Professor Richard Mara, who taught the foundational physics classes at Gettysburg College ca. 1980. Professor Mara exhibited an enthusiasm and excitement for teaching science that just pulled the class along. You could tell that he really wanted us to understand the concepts, using both equations for the more mathematically inclined and also diagrams for the more visually inclined. From this experience, I learned that you have to be knowledgeable and excited about the subject matter and also truly invested in having students understand (not regurgitate) concepts to achieve true learning. This was true in the 1980s and is even more true in 2024, given the competition for students’ time, be it social media, activities, work and/or research, and juggling classes as well as interest in the subject.

Infectious enthusiasm and transparency can engage students, but to reach what I think of as true student learning, students need to internalize and connect to the material by actually touching and experiencing the concept. To help us internalize a concept (something like rotational kinematics), Professor Mara presented the big picture by explaining where we had been (translational motion) and how that related to the new topic (rotational motion). Using equations, diagrams (with colored chalk), a few words, and many homework problems (in class and outside), we were able to internalize the “concept” of rotational inertia. However, to really connect, Professor Mara used demonstrations, which he saw as the only way to really learn. For example, I went to Professor Mara and explained that I was going to catch an early bus home for fall break and would miss class. I recall his exact words: although it was my choice, he would really like to see me participate because this was “demonstration day” where we would get hands-on experience with fundamental concepts from class. These weren’t canned laboratories but manifestations of abstract physical concepts. One demonstration had a heavy wheel with an axel sticking out of the center to hold onto. After he rotated the wheel, he said, “Mr. Composto, turn now.” I turned the wheel and went flying across the room due to the torque exerted by the turning wheel. This was the first time that I truly learned how a class concept applies to real life and that, although the math was fun, the actual “feeling” of a concept created a learning experience that I recall like it was yesterday. I was right to go home a little later!

At Penn, I teach a soft matter course to upper class undergraduates from materials science and engineering, chemical and biomolecular engineering, bioengineering, physics and chemistry, where the students learn thought direct contact with materials. This is a class where concepts from physics, chemistry and biology are used to design materials with precise structure-property relationships. The first third of the course is about the basic principles of soft materials (think Jell-O). Here I rely on Professor Mara’s enthusiasm and the promise that applying fundamental concepts from physics, chemistry and biology learned in their first years underline students’ ability to learn to design and create new materials needed for lighter cars, smaller batteries, and tastier souffles. Concepts like viscoelasticity can be brought to life by showing that a toy like Silly Putty can flow like a viscous liquid if pulled slowly or behave like a solid if pulled quickly. The latter is nicely demonstrated (and used to awaken students) by throwing a ball of silly putty at the chalk board and ducking before it rebounds. Paying homage to Professor Mara, students pass silly putty around so they can try for themselves while I then explain the principles underlying this unique behavior. It’s also fun to show them how to imprint a comic strip from a newspaper after introducing them to physical newspapers.

The final two-thirds of the course is even more fun because we discuss the behavior of each type of soft matter, including polymers, colloids (which are very small balls suspended in liquid), surfactants/lipids (things like soaps and cells), and my favorite topic, food. For polymers, we pass around Lycra, a flexible fiber used in your workout clothing, and Kevlar, which is molecularly similar but stronger than steel on a weight basis.

The classes on food, however, most completely cement students’ understanding and delight. In these classes, we discuss the components of chocolate and compare their structural similarity to what they learned when discussing polymers, colloids, etc. We go back to the fundamental concepts about thermodynamics of mixing (equations and diagrams), and I remind them how these concepts also captured the behavior of synthetic materials discussed previously (polymers in sneaker soles). Then I show them that chocolate has multiple incompatible phases that make up its microstructure. We then do a blind taste test with four types of chocolate ranging from very dark (95% and bitter) to white (arguably not chocolate). Eggs too are multiphase material; students see this when they combine egg whites (water/proteins) with egg yolk (water/fats/proteins/carbohydrates). Students also whip up a foam from egg whites and compare its porous structure to a synthetic foam (e.g., polyurethane seat cushion). Again, the purpose is to connect fundamental concepts that appear to only apply to “engineered” soft matter to everyday examples of soft matter so students can internalize concepts rather than memorize them.

Around Halloween, we teach a particularly popular class called Chemistry in Candy Making. Here, I invite food scientists from the Hershey Company to discuss chemical reactions underlying caramelization and Maillard Browning, as well as classification of sugar-based confectionery according to their crystallinity from high (rock candy) to medium (fondants) to low (gummies). We discuss the “sucrose phase diagram,” harkening back to earlier concepts, and show how the cooling pathway of the sugar solution determines whether you have hard candy (amorphous glass) or rock candy (large crystals). The food scientists then demonstrate how to make a Jolly Rancher hard candy (including the trade secret coloring/flavor) and a highly aerated candy like marshmallows (another example of a porous foam). The class ends with two huge bags of candy of the Hershey power brands (Reese’s and Kit Kat) and other brands (Good & Plenty, York Peppermint Pattie).

One goal of this class is to demonstrate to students that learning is fun and that the concepts we teach in class have many applications if they think creatively. Another goal is to get students to think broadly and creatively about the fundamental principles of engineering. Rather than memorizing that this type of material behaves in a certain way, students see that the concepts are broadly applicable if they only look deeper. Beyond science, students ask about career paths (Q: do I need to study food science? A: no, any STEM degree is fine because you learn on the job). Having students have fun, learn concepts, and better understand career opportunities may be the most useful type of classroom learning because it combines so many opportunities for students to be curious and develop as critical thinkers.