The "1d6 per 10 feet of falling, with a maximum of 20d6" rule is simple, but not very realistic (yes, I know, we have wizards and Jedi and stuff in these games, but a little more verisimilitude for falling would be nice).
As any physicist will tell you, your momentum is what causes the damage when you hit the ground, not the distance - and small light things have a lower maximum speed when falling than big dense things.
I propose that the number of dice of damage one takes from falling be equal to one tenth of the speed in feet per second.
Of course, in an RPG, we're more aware of the distance something will fall than we are of the speed you'll be going when you hit. So, I looked up the maths, and found that in
feet per second, it's quite easy to work out:
- Speed = square root of (Distance x 64)
Armed with the speed, we can work out how many dice we need for the damage... but momentum (which is what hurts you when it's all converted into bludgeoning damage) isn't just about your speed: your weight is important too.
From the d20 modern rules for vehicle collisions, I saw that smaller objects inflict lower damage by using a smaller die type. Simple and easy to apply. In real life, hamsters can fall almost indefinitely without sustaining any injuries because they're so light and fluffy, whereas an elephant will break limbs if it falls just a dozen feet or so.
For other rules systems where size categories aren't as clearly defined, I've given examples of things that are the sizes.
- Fine (fly) = 1
- Diminutive (hamster) = 1d2
- Tiny (cat) = 1d3
- Small (halfling) = 1d4
- Medium (adult human) = 1d6
- Large (horse) = 1d8
- Huge (elephant) = 1d10
- Gargantuan (baleen whale) = 1d12
- Colossal (Godzilla) = 1d20
Lastly, how fast do things fall before their wind resistance matches gravity? Numbering the size categories from Fine to Colossal, I found a whole bunch of examples, and made this rule:
- Terminal Velocity = Size category squared x 10
(This rule closely follows real life terminal velocities without needing too much maths.)Any time the distance fallen shows that the speed is higher than this amount, change it to the terminal velocity.
Summing up:- Falls greater than your own height risk damage
- Number of dice = speed / 10
- Maximum number of dice = size category squared
- Speed = square root of (Distance x 64)
- Type of die = one step per size category (where 'Fine' = d1)
This still means that a tough high level character can walk away from
any fall (as long as he's not gargantuan). How to fix that? I suggest that half of falling damage is applied to CON, save for half (3.5 versions of D&D would use a Fortitude save with a DC equal to the number of dice, AD&D would probably use a Petrification save).
If you've read this far, thanks! I'd like your opinion: it's a big new rule - does it all add up? Would it be easy enough to use?