Science Question

A piano tuner frequently utilizes the phenomenon of beats to tune a piano string. She will pluck the string and tap a tuning fork at the same time. If the two sound sources - the piano string and the tuning fork - produce detectable beats then their frequencies are not identical. She will then adjust the tension of the piano string and repeat the process until the beats can no longer be heard. As the piano string becomes more in tune with the tuning fork, the beat frequency will be reduced and approach 0 Hz. When beats are no longer heard, the piano string is tuned to the tuning fork; that is, they play the same frequency. The process allows a piano tuner to match the strings' frequency to the frequency of a standardized set of tuning forks.
The tuner lowers the pitch of the string by loosening it, the difference between the two vibration rates will become greater and the beats will get faster; if she raises the pitch by tightening the string, the beats will slow down as the string vibration rate approaches that of the tuning fork, and eventually will disappear.
Hope this helps. Susu