for (int i = 0; i < nContacts; i++) {
        // access data from collision detector
        point = mCollisionDetector->getContact(i).point; // contact point
        normal = mCollisionDetector->getContact(i).normal; // normal vector of contact point
        RigidBody *A = mCollisionDetector->getContact(i).rb1;
        RigidBody *B = mCollisionDetector->getContact(i).rb2;
        pVelocity = mCollisionDetector->getContact(i).pinataVelocity;

        // pre-impulse normal velocity
		double vN = normal.dot(deriveContactPoint(A) - deriveContactPoint(B));
        // compute j
        j = -(1 + epsilon) * vN / (denominator(A) + denominator(B));

        // update linear and angular momentum
        updateMomentum(A);
		normal = -normal;
		updateMomentum(B);
    }