Having no recollection of either in the catalog of my experience I will nonetheless render the following as a possible hypothesis:
In light of the equation relating the equivalence between matter and energy E=mc� and in compliance with the law of the conservation of matter and energy which allows for one being manifest as the other I submit that upon meeting they exchange identities through a
transformation of each into the other henceforth to carry on as though no interaction took place, the unstoppable force becoming the immovable object and the newly converted unstoppable force continuing on in the same direction, away from the resultant immovable object.