Gerion of Mercadia said:
Alright, continue the example - If I cast Fly instead of continuing to fall when do I take the 10d6 damage for falling the 100ft? Before or after the casting? Or never?
You don't, since you don't complete the fall. The damage you take is from falling and completing that fall- without interruption (such as from a
fly spell, or even a last-second
feather fall spell. Thankfully, D&D more or less ignores inertia.
Once the fall "starts", must it complete? It's not the falling that does the damage, it is the IMPACT at the end. The second question is answered in the same manner as the first, Impact cares little wether [sic] you hit the object or the object hits you.
You're right it is the impact that does the damage. Hence, if you never impact, you don't take the damage from falling.
There have been rules created for D&D that deal with a falling creature/object impacting the ground (or other object), as well as rules made for objects falling on a creature/object.
To take damage from falling, you must actually impact something. If the fall is interrupted, you aren't falling anymore. If you fall again, you take damage according to the height of your new fall.
In the case of a character who cast
fly and used his fly speed to fly to the ground, the distance is 0 and he takes no damage. If the spell ends while he's aloft, he has 1d6 rounds in which he falls 60 feet per round (like feather fall). If he's still in the air after that time expires, he begins a new fall.
In the case of a character who cast feather fall from high up in the sky. Say that he's a 800 feet up in the air, and that he's a 10th-level wizard. If he cast feather fall the moment he started falling, he'd float gently for 600 feet (this takes 10 rounds), then resume falling when he's 200 feet up. His falling was interrupted, resuming at 200 feet. Presuming no other interruption, he'd take 20d6 points of falling damage. He's no better off that he would be falling the full distance.
Clearly he'd be better off initially in freefall for two rounds (1st round 150 feet, 2nd round 300 feet are fallen), then cast feather fall at the beginning of the 3rd round. His fall is interrupted at 350 feet, and and reaches the ground 6 rounds later. He takes no damage, because his fall resumes when feather fall ends. That is, when he is on the ground (0 feet above the ground). No damage is taken.
He could save time and continue to fall in the 3rd round, casting feather fall when he's 50 feet above the ground at the beginning of the 4th round. He'd fall gently to the ground due to feather fall. As above, he takes no damage.
If you interrupt a fall, you take no damage. If you fall again, you take damage according to your new fall. If your new fall is interrupted too, you take no damage from that fall either.
Falls don't need to complete, but if they do, a creature object takes damage according to the "falling" rules. If an creature/object is struck by a falling object, they take damage according to the "falling object" rule. They are abstracted and work well enough, IMO.
Q: Weapons (as you insist on using the undefined term) deal damage in one of three exclusive categories, slashing, bludgeoning and piercing. Of which of these categories is the extra damage? A: NONE
Why?
Because they are energy damage, that's why. In the case of the flaming quality, it's fire damage. In the case of the vicious quality it's "a flash of disruptive energy".
Darn, somebody is getting an attitude, and it isn't Me.

Asking seemingly dumb questions to illicit flippant answers and expose the reasoning as "because I say so" instead of "its the rule" is my tactic. I'll just leave this one alone until tomorrow.
As much as I like them, playing word games isn't exactly pertinent in a rules discussion though. Wouldn't you agree?