When a performer sees a dynamics notation, such as pp for pianissimo, (or p, or f or ff, or any of its siblings), in a written score, which notes are to be played softly?
 I take it the symbol means "Start playing softly now, and continue playing softly until you are instructed otherwise." How long does this instruction last? To the end of the measure? The end of the line? The end of the song?
 If the composer wants to end the pianissimo, what symbol would be used to indicate "That's enough playing softly. Go back to playing normally now."
 How would the composer indicate that a single note be played softly?
 And specifically, how would the composer indicate that a single note within a chord should be played softly?