Worm, you're looking for academic problems! Who says you are accelerating? You might be going around with barely a speed change, but pitching up. The question is why does it pitch up ? Answer - because the thrust line is low and below the c of g. The force isn't applied at the centre of mass, it's below it. There are other balancing forces to compensate (hopefully)- ie the pilot frantically pushing the stick forward to apply an upload on the tail.
I've done advanced physics, but this makes no sense:
"Alternatively, if the aircraft maintains the same speed and climbs, the balancing force is a greater aftward component of weight, at the centre of mass."
The morale again is: don't look too deeply for academic problems!