This is stupid. There is no such thing as an unmoveable force because all matter is moving, or vibrating, constantly. The absense of complete movement is at absolute zero, the utter lack of energy, and is impossible to reach. However, unstoppable forces are more realistic, but they faze out after a very long time and can pass through most objects, like radio waves. The best answer I can provide is that the unstoppable object will pass through the \"heavy stationary\" object, or simply bounce off and continue its trajectory in a different direction.