Rigidbody and dynamic gravity

Hello everybody,

I have question concerning a rigidbody and a dynamic gravity system. I deactivate use gravity because i need to have a control on my gameobject (can move, jump...). When I have a gravity vector (0, -10, 10) the object is not falling right...it moves in the x direction I don't understand why because I only have the line :

 void FixedUpdate(){rigidbody.AddForce(Physics.gravity);}

I don't understand why the rb is not following the gravity vector and changes x. Can somebody help me or give me an idea to make a rigidbody affected by a changing gravity system.

Thanks a lot.