1. Students are asked to line up at the front of the classroom and represent particles being displaced in a periodic system with repeat distance $a$.
  2. The instructor will represent a point in the envelope function of constant amplitude; as the instructor walks in front of the particles, each student particle will oscillate up and down to create an envelope function.
  3. The same process is repeated with several different wavelengths for the envelope function.
  4. After the first group acts out an envelope function, the class can be asked:

SWBQ: If I was moving at velocity $\frac{a}{1 \sec}$, what is the frequency at which the particles bounced up and down?

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