Hmm.. i have been wondering this for some time now.

If a string instrument were to play with the biw, and then change the direction of the bow, would this create a brand new note? Or would it be a new note?

I have often seen music written for strings where many semibreves are tied together over many bars.. is this only possible when played by string sections? Or can singular instruments produce this effect?

Sorry for my bad grammar

I'm not sure if i understood correctly so maybe someone can correct me but
yes if you change bow then you get a new note but the idea is to make your bow changes as smooth as possible when playing long notes over several bows, to make it sound like there are no bow changes. if a whole string section was playing it then they may change bows at different times so you can't hear the changes

You can hide your bow changes on really long held notes if your vibrato is secure, although most violinists will train themselves to play very slow long bows as a tone exercise, the idea being that you can hold a single note for as long as possible and still produce a nice tone.

I still do this daily, but I find it hard to get beyond 36 seconds without the tone going scratchy. Pah.

I do this too - i thought it'd never pay off, but realised it does when we were doing Shostakovich's 7th symphony in youth orchestra and i could play a whole page of tied G-string A's in 2 bows !