Small code snippet reference for getting lifelike gravity from your accelerometer in your projects. This is for Cocos2D and Box2D but is easily changeable to your project needs whichever language you program in.

- (void)accelerometer:(UIAccelerometer*)accelerometer didAccelerate:(UIAcceleration*)acceleration
{
b2Vec2 gravity ( 9.8 * acceleration.x, acceleration.y * 9.8);
world->SetGravity(gravity);
}