in episode 4 Han solo never heard of the force, chewbaca never says he have ether but in episode 3 chewbaca's people battle the droids army and chewy was with yoda, so he should know about the force no?
No .... Han never said that. Luke assumed he didn't believe in the Force and Han skirted around the question, comparing it to a 'hokey old religion'.
As for Chewy, we only have Han's responces and reactions to really tell what he is saying ... and Han, being rather world weary and sarcastic, might not acknowledge or even understand everything the Wookiee has to say about the Force, even if he ever did speak of it. I tend to see Chewie to be rather tight lipped about such personal matters, even toward Han, especially considering his own beliefs, which I'm sure he was relatively vocal about .... It's really difficult to say what Chewbacca's views are, but he does seem a bit more stoic and honor bound than Solo ... at least in Episode 4.
It is noteworthy to point out that the aging Jedi, Obi-Wan appears to be slightly more than a casual acquaintance to the Wookiee in Mos Eisley ... He strolls right up to Chewie and begins discussing terms of their mission to Alderaan. This struck me odd, even in the 70s ... the old guy seems to have no fear in approaching a fierce alien with a reputation for violence, as was revealed by Solo just a bit later and as was demonstrated on the Death Star.
In Episode 3, we understand why, because of the struggle on Kashyyyk, where Yoda commanded the armed resistance. Furthermore, Chewie in particular aided Yoda in his escape from the world ... considering that Yoda had further teaching for Obi Wan in his exile to Tatooine in the form of merging with the living Force (as he was to learn from Qui Gon Jinn from the beyond ...), it is quite possible Yoda also told Obi Wan to seek out Chewbacca for assistance as a being who could be trusted during the time of darkness ... That is speculation, of course.
R2-D2 is unique in the saga, as he was present for nearly all of it and retains all of his memories. However, we are also given the impression that even though he is generally cheerful and helpful, he also has a rather crude, smartass, and cantankerous disposition at times. Because his memory banks have never been reset to their default settings, he has developed a complete personality; much like we see happening to Threepio through episodes 4-6 - he, who started as an interpreter and not very good at telling stories to a creative yarn spinner - complete with sound effects and gestures - as he recounts their story to the Ewok tribe on Endor.
Because we must view Artoo as a fully developed personality, he is, in effect a living being, capable of creativity and deception. This is why I think Artoo has such a special place among the Rebel Alliance, not just because he once carried the Death Star data tapes. The Alliance personell don't seem to treat him as just another droid, even though he can play that part very well ... Those who know the droid realize he is more than he seems.
Therefore, yes, Artoo would lie to complete his mission ... but even more so, lure Luke to Obi Wan as well. Artoo had to completely recognize where he was and who his new master was on Tatooine. He would realize the boy's importance to Obi Wan, even if he didn't truly understand the Force.
In a lot of ways, Artoo De-too may have been the single most important secret operative the Rebel Alliance ever had, whether they knew it or not.
JM.