In Beethoven's Pathetique, how do you play the fortepiano chords in the third movement (rondo)? I can easily do this on a wind instrument by changing wind speed, but on piano, I have no idea how to play it.
I tried using the 'delayed pedal' method where you strike the chord as if it were staccato and pressing the damper pedal a few moments later, but that doesn't give me a good result because it is very hard to time accurately, leading to chords that are often too loud or soft.
Throughout classical piano music, there are nonsensical dynamics markings that are impossible to execute literally. If you think playing one note fp is hard, there are many places where classical composers ask a pianist to play (or at least start) a crescendo on a long held note. This practice persisted at least well into the 20th century.
These kinds of markings aren't meant to be taken literally. In this case, just treat fp as a big accent - play a loud note followed by soft notes.
Because of the decay on a piano (and it was more significant back in Beethoven's day), every note is fp anyway - it's just that when a note is followed by other loud notes, we've learned to suspend our disbelief and aurally pretend that the piano can actually sustain volume.
That's how I would do it. Play a staccato chord, then 'catch' the sound with the damper pedal. It takes a fair bit of practice, but when you time it right, and play the notes at the correct volume, that's it - job done.
In piano music, fp (forte-piano) chords are played as if they are forte, then immediately followed by piano-volume (i.e. quiet) music. So I'd recommend you do just that--play the forte chord loud, and the following music quietly.
Fortepiano and Sforzando basically mean the same thing in piano scores. Just treat the fp as an sfz(big accent on the first chord, quiet after the chord) and you'll do fine. I go a bit to the extreme with my own interpretation, a forte dynamic followed by a dynamic closer to pianissimo than piano, a mezzo pianissimo in a sense. But, you don't have to do that. Just treat fp as if Beethoven wrote sfz, since they are equivalent in piano scores.
The edition I have shows separate forte and piano dynamics but that is just an editor's choice.
