Quick Question on Trill Execution

[penguin_pianist]

I am beginning to learn the Scarlatti sonata K1. With what fingers and for how long/fast should I execute the trills on the last beats of measures, say, 2,3 and 4 (quarter note trills)? Should I begin on the upper (auxillary) note or lower (written) note?

You can find the score here: https://www.sheetmusicfox.com/Scarlatti/1.pdf

[faustsaccomplice]

hey,
first of all, begin the trill on the written note, because it's the same as the previous note. 

the execution (speed, length) are really up to you.  i think five notes in total would work on these.

a trick with trills is to play them just barely slower than is your maximum speed (if you want them fast).  you should never feel like you're pushing for it because it will become uneven, which is much worse than too slow.  of course trills don't have to be literally even, but even in sound.

hope that helps some. 

[penguin_pianist]

What about the quarter note trills in the right hand in measures 8 and 9? On what note should I begin those?

[faustsaccomplice]

again, on the written note, because the melody is oscillating from a to g.  it would sound weird to start it on the auxillary.

[penguin_pianist]

What about the examples given here:
https://www.oldflutes.com/articles/classicaltrill/index.htm

If I start on the auxiliary note, the first set of trills is awkward. If I start on the principal note, the second set is awkward.

[faustsaccomplice]

that's a pretty thorough article, which i read a bit of just now.  i think that it's helpful to know those things.  i'd certainly take that all into consideration if i were you.   however, it seems to be common performance practice (at least these days) to play trills like that beginning on the written note.  furthermore, it sounds right (to me). 

i think the second set of trills will become easy for you.  just don't try to fit too many notes into the trill.