Bach ornament help

[doverbay]

I'm trying to learn the Bach/Marcello Adagio and am having a problem with the trills and
mordents. 
As I understand it from an explanation of Bach's ornaments is this.
For the mordents I should go down 1/2 step from what is written? or is it
one note in that scale?
And the trills I should start one whole step above?
My copy of the music has a mordent at bar 5/7/9/11.

This piece is in F Major.
So when I do a mordent on a b/flat I should play the A natural, or A/flat etc.
When I do a mordent on the A I should play the A/Flat? or G.
When I play a mordent on the g should I play G/Flat or F?
I hope I'm explaining this well enough to be understood.

[j_menz]

I'm trying to learn the Bach/Marcello Adagio and am having a problem with the trills and
mordents. 
As I understand it from an explanation of Bach's ornaments is this.
For the mordents I should go down 1/2 step from what is written? or is it
one note in that scale?
And the trills I should start one whole step above?
My copy of the music has a mordent at bar 5/7/9/11.

This piece is in F Major.
So when I do a mordent on a b/flat I should play the A natural, or A/flat etc.
When I do a mordent on the A I should play the A/Flat? or G.
When I play a mordent on the g should I play G/Flat or F?
I hope I'm explaining this well enough to be understood.

Keep to the notes of the scale. With the trill, the trilling notes are the note and the note above it on the scale (so G trills on A but A trills on Bb). Same with the mordants, so for you last 3 questions,  A natural, G, F.

One caution -  if a small accidental appears with the ornament, it will change that - so a flat sign above the trill will mean the trill note is dropped a semitone, likewise with the mordant.

[iansinclair]

And yes, a trill starts on the note above (a plain trill that is).  Some mordents are notated to start on the note below.  Some fancier ones may also have the next to the last note of the trill on the note below (this will be notated).

One other item.  Ideally, the trill is in the meter, usually twice as fast as the smallest notated division in the measure (for instance, if the small divisions in the measure are eighth notes, the trill will sixteenths).  Occasionally this is varied with the trill being four times as fast, but that's not common.

[doverbay]

Well I want to thank you very muchly for that explanation.