1. Excitation: When the fork's tines are struck against the glass, it sets the glass into vibration. The fork transfers its energy to the glass, causing it to vibrate at a specific frequency.
2. Resonance: The glass, being a solid object, has a natural frequency at which it tends to vibrate. This natural frequency depends on the physical properties of the glass, such as its elasticity, density, and shape. When the frequency of the fork's vibrations matches the natural frequency of the glass, resonance occurs.
3. Amplification of sound: At resonance, the vibrations of the glass are amplified, causing the sound waves to become louder and more sustained. The water inside the glass also plays a role in enhancing the sound by acting as a medium for the sound waves to propagate.
4. Radiation of sound: The amplified sound waves radiate from the glass, reaching our ears and allowing us to hear the distinct ringing sound. The pitch of the sound corresponds to the frequency of the vibration, which is determined by the natural frequency of the glass.
In summary, the combination of the fork's vibrations, the glass's natural frequency, and the amplification and radiation of sound waves produce the characteristic sound when glass cups filled with water are tapped with a fork.