Final answer:
When section A first returns in movement 2 of Eine Kleine Nachtmusik, the dynamics are different. Dynamics control amplitude, which affects how loud or soft the music is played, altering the music's mood and expression.
Step-by-step explanation:
When section A returns the first time in movement 2 of Eine Kleine Nachtmusik, the element that is different is the dynamics. In classical music, variations in dynamics refer to changes in the amplitude of the sound, which corresponds to how loud or soft the music is played.
When this section returns, the composer may have intended for it to be played softer (piano) or louder (forte) than it was initially introduced. This change in dynamics can have a significant impact on the mood and expression of the music.
In related terms, the texture of a piece refers to how many layers of sound are heard at once and how they interact. If the texture were different, it might involve adding or subtracting instruments or changing the role they play.
The melody and the harmony could also change, affecting the tune and chord progressions, though these elements are typically more noticeable than dynamics.