September 19, 2024
Process-Based Physics Education

Principles or formulas? Content or process? Effective physics education focuses on all of these, and more.

A meme making the rounds of social media attributes the following quote to Richard Feynman: "Teach principles, not formulas. Understand, don't memorize." If Feynman actually said this, and and I cannot find a definitive source proving he did, it would be out of character for him to be so imprecise. I suspect there was context around this statement the meme is ignoring.

While it's certainly true that memorizing facts and formulas isn't a useful approach to learning physics, ignoring facts and formulas is equally stifling. Formulas are the concise and powerful outcome of our physical understanding of the world, and spoken-word principles don't give us the insights needed to put our knowledge to work.

As an example, let's consider Einstein's theory of special relativity. Its principles include two postulates—that physical laws are identical in all inertial reference frames, and that the speed of light is the same for all observers. Working the postulates into classical kinematics and dynamics yields additional principles, notably mass-energy equivalence and the existence of a spacetime continuum governed by time dilation and length contraction. Reading about the elasticity of space and time predicted the the theory of special relativity has been a source of wonder for physicists and layman alike. But why stop there?

Special relativity formulas rely on the same algebra most of us learned in high school.

With these formulas and a little Googling for values, we can learn why time dilation and length contraction are not readily observable at the typical speeds of terrestrial objects. Or we can determine that the energy produced by a typical nuclear power plant in a day can be obtained from about one gram of matter, the mass of a small paper clip.

A third important consideration, beyond principles and formulas, is the connection between the two: In other words, the answer to the question, "Where do formulas come from?" The time dilation formula above can be derived from the principles of special relativity using simple geometry.

Finally, it's worth getting to the bottom of how experimental inquiry, in this case the Michaelson and Morley experiment which established the invariability of the speed of light, leads to the development of new principles and formulas.

In all of these ways, revealing to students the processes of physics, and expecting them to draw evidence-based conclusions from data, from principles, and from formulas, builds in them the confidence needed to become rational problem solvers in their careers and in their lives. The curricula of the present-day AP Physics courses—their dependence on requiring students to "justify their answer," "explain their reasoning," "determine," and "calculate"—encourage students to engage in the processes of physics. Process-based activities and assessment can be infused into physics courses at all levels.

As "grist for the mill," memorization of principles and content is a good thing, so long as it doesn't end there. Process (laboratory inquiry, derivation, applied reasoning) is the "string" connecting content (principles and formulas) into a web of understanding.