I would like to know how to detect the direction of an object with physics, I mean when is falling down. can it be by a eventListener? any idea how to do it?
I need it for know can I change the spriteSheet.
To find the exact angle based on an objects velocity you'd call:
local angle = atan2(xVelocity, yVelocity)
This returns the angle in radians, which you can then convert to degrees. This allows for more precise control over the object. Daniel Shiffman wrote a great book involving many aspects of physics simulation over at http://natureofcode.com/book/.