Smooth motion rigidbody

Why does this code make my rigidbody stutter and not move smoothely?

private void FixedUpdate(){
   //rigidbody.velocity = new Vector2(3.0f, rigidbody.velocity.y); (also stuttering)
   rigidbody.MovePosition(transform.position + Vector3.right * 3.0f * Time.fixedDeltaTime);

Maybe it doesnt rely on your Code, in my Case the Friction between the Ground and the Player caused him to stutter. Try turning that off with a Physics-Material on the Player.