Pre-class Example #2: Student Responses

 

1. What frequencies give rise to growing oscillations?

2. Why are these frequencies effective?

  1. any multiple of the natural frequency so the drive will periodically act in the direction of motion.

  2. any fraction of the natural frequency: net positive work only occurs when the force switches and the force acts over a distance.

  3. only odd fractions of the natural frequency so that the drive spends more time acting in the direction of motion (positive work) and less against it. (CORRECT)

A more mathematical response: the oscillator is driven by the Fourier components of the square wave.