There are a few reasons why a tuning fork is struck against a hard surface rather than simply being plucked or tapped. First, striking the tuning fork creates a louder, more sustained sound that is easier to hear. This is important because when tuning an instrument, it is necessary to listen carefully to the pitch of the tuning fork and compare it to the pitch of the instrument. Second, striking the tuning fork against a hard surface helps to create a pure, harmonic sound that is free of overtones. This makes it easier to hear the exact pitch of the tuning fork, which is essential for tuning an instrument accurately.
In addition to being used to tune musical instruments, tuning forks are also used in a variety of other applications, such as soundproofing, vibration analysis, and medical diagnostics.