When reading [this article on the debris they found from Flight MH370][1] they mention a lab in France that is supposed to be able to look at the debris (a flaperon), and figure out if the flight had exploded in mid-air or if it had broken up on impact with the ocean.

This has left me wondering, how would they do that?  How can you tell from an exterior control surface<sup>1</sup> that the plane had exploded or broken up on impact?

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<sup>1</sup> *Examples may include elevons, flaperons, ailerons, elevators, basically anything that helps the plane maneuver and is exterior to the fuselage.*


  [1]: http://www.cnn.com/2015/07/31/world/mh370-debris-investigation/