reversing gravity for particular GameObjects

hi guys, i have some gameobjects that i want to fall upwards when they enter inside a trigger using this.
var gravity : float = -9.81;
function OnTriggerStay (other : Collider) {
//other.attachedRigidbody.isKinematic = true;
//Physics.gravity = Vector3(0, -9.81, 0);
//gravity = - gravity;

Physics.gravity.y = -Physics.gravity.y;

but when my selected gameobjects enter the trigger, every other rigidbody gameobject in my scene fall upwards.
please how do i apply this for the gameobects in the trigger only,like this, for isKinematics.
//other.attachedRigidbody.isKinematic = true;
where other refers to objects in trigger alone. thanks


rigidbody.useGravity = false;

Then apply a y velocity so that your guys goes upward.
When leaving the box, remove the velocity and reset the gravity.