The G chord on the piano is not sharpened due to the historical tuning system and the physics of sound waves. The standard tuning system, known as equal temperament, divides the octave into twelve equal parts. This system was adopted to simplify the tuning of instruments and to allow for the playing of a wide variety of music. However, it results in some slight discrepancies in the tuning of individual notes, including the G note.

In the equal temperament system, the frequency of the G note is set to 392 Hz. This is a compromise between the pure interval of a perfect fifth and the natural tuning of the note. A perfect fifth is the interval between two notes that sound harmonious when played together, and it is the basis for the tuning of many instruments. The natural tuning of the G note, however, is slightly lower than 392 Hz. This discrepancy is due to the physics of sound waves and the way they resonate in the instrument's body.

The natural frequency of the G note is approximately 384 Hz. This means that if the G note were tuned to its natural frequency, it would be slightly flat compared to the standard tuning. To maintain the integrity of the equal temperament system and the harmonious relationships between notes, the G note is slightly sharpened to 392 Hz. This adjustment ensures that the G note remains in tune with the rest of the keyboard and that the intervals between notes are consistent.

Data from the Acoustical Society of America (ASA) supports this explanation. According to their research, the natural frequency of the G note is indeed around 384 Hz, while the standard tuning frequency is 392 Hz. This difference is a result of the physics of sound waves and the need to maintain the equal temperament tuning system. The slight sharpening of the G note is a necessary compromise to ensure the overall tuning of the piano remains harmonious and in tune with the rest of the music being played.