void update(float tpf) {
        assert tpf >= 0f : tpf;

        if (kinematicWeight > 0f) {
            kinematicUpdate(tpf);
        } else {
            dynamicUpdate();
        }
    }
Internal callback, invoked once per frame during the logical-state
update, provided the control is added to a scene.

@param tpf the time interval between frames (in seconds, &ge;0)
jme3-jbullet/src/main/java/com/jme3/bullet/animation/PhysicsLink.java