why is t i find barre chords easier on electric guitar as appose to acoustic
Acoustics usually have heavier strings - thus, higher "string tension" as Tom noted. But a guitar's action (how high the strings are above the fretboard) effects barre chord ease for both acoustics and electrics.
Generally speaking, acoustic guitars require a little more muscle than electrics. But you can build those muscles with regular practicing on your acoustic!
Fingerboard radius does affect the ease of a clean sounding chord when "Barred." This does open up another can of subjective worms as I find a flatter radius to be actually easier when barring chords, especially when getting the 1st and 2nd string to be fretted cleanly - vintage style radius' with more of a curvature are notoriously difficult for me to get a good clean barre chord. Outside of the radius, I think the other biggie is the tension of the strings, which has to do w/ the particular gauge and scale length of the guitar.
No, not newer ones. Old Fenders, sure. But guitars like Jacksons that are built for soloing will flatten out to a 16" radius.
Much of the discussion (an I believe correct answers) here is on why it's easier on one guitar than another, but the main question should be, "why is it causing difficulty at all?" From years of teaching I have found that most players tend to have poor technique when it comes to playing barre chords. There is a thought that if the strings buzz then I must squeeze harder. In actuality it's about placement (the finger making the barre) and gravity (the arm pulling down rather than the hand squeezing). This should cause the implied problem of one easier than another to be a non-issue.
Electrics can use much lighter srings than acoustics, and especially if they are flat-wound, they are much easier to play. I agree with David Lenef that you should practice barre chords on acoustics to build up both finger muscle and finger memory. And not just simpler patterns like the A (major, major 7th, minor, minor 7th) and E (same as A), but the C. If you can play the F on the fifth fret using the C pattern and be able to work it into your playing without missing a beat, the skills you're acquiring will improve your playing greatly. Once I shed all reluctance to play barre chords, my knowledge of the fret board grew exponantially. I also use the capo less.
Mentioned elsewhere on this forum (from posts from around 2 years ago), I ran across one member who mentioned that he trains his students to draw back using muscles in their arms to barre more efficiently. I think this is borrowing from a classical technique, but he implied that he's using it to apply to steel string. I can't say I've put a lot of practice into it, and I'm in no way classically trained, but the theory seems solid enough. It may be something worth exploring if they're giving you a whole lot of trouble.
Per member Donna Zitzelberger:
"Also,another trick I wanted to mention - the gurus of bar chording are found in the classical world. I've been really blessed to study with Jim Smith at USC and also audit classes taught by Pepe Romero. They constantly tell the students to use the full weight of the arm when making a bar chord and not to squeeze the thumb and middle finger. The full weight of the arm uses huge muscles to hold the bar down and relieves the tiny muscles of the hand from getting worn out. The result is much more stamina in playing."
I couldn't agree this statement more. I am a classically trained guitarists and the focus on the whole arm rather than the "tiny muscles" of the hand is very effective. Barre chords are in almost every concert piece played on the classical guitar and therefore the technique used to play them must not wear the hand out. Otherwise, you'd have a twenty minute concert vs. an hour and a half concert.
William Kanengiser does an excellent job discussing the mechanics of barre chords in his Effortless Classical Guitar DVD. Recommend it for any style of guitar playing.