Have tu ever noticed this?

I think maybe it was for 3 reasons...1..in New Moon they were young lobos and they werent at their full strength...2..in Eclipse...Jacob was bigger and stronger...3...different director....

Also, in addition to what Hellohoudini said, one was a slap and the other was a punch.

I could go slap a stone muro right now and it won't hurt that much, but if I were to puñetazo, ponche a stone wall, I'd likely break my hand.
It's a sciency involving pressure and force per unit area.

I figured the only reason Paul flinched was because Bella's slap did something to his ego, which explains why he got so angry.
Jacob was shameless.

Awesome observation, girl! Kudos for you! And no, I never thought of that before tu dicho so. Thanks for another wake up call! ;D

No but that is a good point

yah i have, but I always thought that it was just that Paul had bigger anger issues then Jacob, plus Jacob's was in amor with Bella so...

I think there's no right explanation because there's no such a thing in books. SM didn't made up that scene.
In book Paul was just angry because Bella fund out about wolves.She didn't slap him.
But... probably it was because Paul didn't expect slap while Jake was ready for everything. He know that there'll be consequencesfor his action.