Doors suddenly closing, curtains billowing
There were two factors here.
1. The Mechanics of Rotary Motion. The door moves in a rotary manner; it moved around the hinged edge. There are Laws of Mechanics which explain this, but they are a bit involved
So, let us consider a simpler explanation, based on these Laws, using the extremities of the rotary motion. Say, in the same situation as in Madeleines bedroom, a window was open and a gust came thru it. That gust would be termed as a force.
i) If the door were completely open, only the edge of the door would be receiving that force. The force according to these Laws would have virtually no rotary turning moment, the force would almost all go into the hinge. The door would not move.
ii) If the door were almost closed, most of its face would be at almost right angles to the force (the gust) and the force would divide into two forces upon hitting the door, the major part causing a rotary turning moment, with just a little going into the hinge. If the gust were strong enough, the door would slam.
From this it goes without saying that the closer the door was to being shut, the greater the turning moment on it. The closer it was to be fully open the less likely it would be to slam shut. Hence as Kate closed it the turning moment increased and combined with a gust the door tried to slam shut
2. The wind was gusting at up to 20mph. An unexpected gust could have caused the door to suddenly close. A slightly open window, or door, on the south or east of the building would accentuate it. In other words a through draft.,
But with a strong gust it could have happened anyway.
Hope I have explained this so that everyone can understand..