TITLE: When a pen is thrown on the ground, why doesn't the whole pen seem to be vibrating even though it makes a sound?
QUESTION [0 upvotes]: Is that because the vibration is reflected back by the boundaries of the pen, a standing wave is produced, and the nodes are so close and so numerous that it seems like the pen is not vibrating at all?
Or is it just because our eyes cannot detect its motion for some reason?

REPLY [2 votes]: Or is it just because our eyes cannot detect its motion for some
  reason?

This is the primary reason, first, because the frequencies of pen vibrations are in hundreds or thousands cycles per second, which is well beyond what we could discern, and, second, because the amplitude of these vibrations is very small.
The distance between the nodes should not be a problem, since, for dominant vibration modes, it should be on the order of inches.
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