The problem with momentum is that is, unfortunately, conserved. Dennis's spectacularly miscalculated dive -- there's a reason he never made it onto any of the school sports teams -- fails to miraculously stop at the point at which he knows he's missed and, in due accordance with physics, continues until he bounces off the shelves and crashes into Sarah Jane in an unwieldy tangle of limbs and falling books.

"Did we get it?" He manages to gasp out from somewhere in the mess. "Did we get it?"