Originally Posted by John Farley
The force from the seats is only applied for very small fraction of a second so the nose down velocity resulting from the acceleration would not be measurable.
The time for which the force is applied is short indeed, but the force is huge. Huge enough to propel the seats and occupants out of the aircraft very quickly. Impulse=force x Dtime. The impulse isn't trying to accellerate that whole aircraft downwars (in this case) it is just applying a derotational force to two points well forward of the c of g - quite a long moment.
Therefore, a bag-seat will impart sufficient force to the aircraft to cause it to pitch down. If the force act long eonugh to accellerate the seats, it has time to act on the aircraft too. Newton never sleeps. Old Chap.