Final answer:
The 9-letter term describing the number of vibrations per second, which determines the pitch of the sound when rubbing a finger around a glass rim, is 'frequency'. This concept is also involved in the phenomenon of resonance, where a glass can shatter if the sound frequency matches the glass's natural frequency.
Step-by-step explanation:
When rubbing your finger on the rim of a glass, the sound's pitch is determined by the frequency, which is the number of vibrations per second. The correct answer to the 9-letter term being described is frequency. This is a fundamental concept of physics related to wave dynamics. The pitch of a sound correlates with the frequency of the vibrations: a higher frequency results in a higher pitch, while a lower frequency results in a lower pitch. The phenomenon of a glass shattering when a singer hits a note that corresponds to the glass's natural frequency is known as resonance. When the sound wave's frequency matches the glass's natural frequency, with enough energy, it can cause the glass to vibrate and potentially shatter.