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Physics Kōans

Conceptual Questions for Peer Instruction

"What is the sound
of one hand clapping?"

In Zen Buddhism a kōan is a story or a question which may cause initial puzzlement, but which leads to enlightenment with further thought and reflection. Familar examples include "If a tree falls in the forest, and there is nobody there to hear it, does it make a sound?"

A physics kōan is a conceptual question that is puzzling at first, but which illuminates or demonstrates physics principles or ideas or concepts. A simple example is "If a cannon ball and a musket ball are dropped at the same time from a tall bulding, which will hit the ground first?"

The choices for answers are generally distinctly different: does it go up, or go down, or stay the same?

Or the question may be based on common misconceptions.

Or they may be predictions for the outcome of demonstrations.

Good physics kōans use and illustrate the application of principles, rather than just encouraging memorization.

For more background on the use of conceptual questions for peer instruction and what constitutes a physics koan see my talk Half and Half Homework: Can peer instruction methods be adapted to physics homework?


Click on a topic to browse through an index of koans on that topic:


I first learned about peer instruction using conceptual questions from Eric Mazur of Harvard University, first from a lecture at a conference on physics education and then from his very useful book
"Peer Instruction - A User's Manual" by Eric Mazur (Prentice Hall, 1997)
The best conceptual questions in this book are most certainly physics kōans (though it may not be that they all are, but they don't all have to be).

How to Use

How I use these in class is similar to Mazur's method:
  1. Present the question, and ask for the "first guess" I tell them not to take too long, just give me your first impression. "The first one doesn't count."

  2. Ask them to show me their answer using the cards. Nobody should be able to see anybody else's answers.

  3. Ask them to talk to their neighbor to compare both answers and the reasoning behind the answer. Who has the better explaination? Can you convince the other person you are right?

  4. Ask them to show their "final" answer. More often than not the students who got it wrong will get it right this time. The students who had guessed the right answer will now have a reason to support their choice, and everyone who got it right (most if not all of the class) will have stronger confidence in their result.

  5. Explain the reasoning. I sometimes ask for a student who found a compelling reason to change their answer to explain how it helped them. I always close by giving my version of the answer to the question, sometimes explaining why it was a tricky question (and they are always somewhat tricky, or it's not worth the time to do this). I never post the solutions.

I do these at the end of a unit, after I've explained the idea, to test their understanding of the idea and to open things up for questions and discussion.

I have found that after I use these in class, even a big lecture class of 80 or more students, I get more questions and more discussion than had I not used these questions.

These kinds of questions work especially well for physical demonstrations. Ask the students to predict the outcome of the demonstration first, and they will pay more attention to the demonstration, the result, and your explanation. The example question of blowing between two sheets of paper shows this, and after folding two cards each student should have two sheets of paper that they can use to try it themselves.

So to get the answer to the question about the two strips of paper, try it yourself. If you don't know the answer to the question about the fox then Google for "What does the fox say?" and view what the fox himself actually says.

Additional Notes

Another source of conceptual questions for peer instruction in Astronomy is
"Peer Instruction for Astronomy" by Paul J. Green (Prentice Hall, 2003)


Eric Myers
Spy Hill Research
Poughkeepsie, New York


Permission is granted to anybody to copy and use these answer cards in any instructional setting, public or private, undergraduate, secondary, or primary. You may not, however, distribute them on-line, nor may you reproduce these in any other published document or textbook, without additional explicit permission of the author.
If you'd like to use them some other way please do contact me. If you want to share them with others, feel free to link to this page. I will likely change this to an appropriate Creative Commons license once I get the chance to choose the proper one.
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