Horizontal falling objects?

[The Souljourner]

You should probably treat it as an inelastic collision (i.e. the guy gets smeared across the face of the thing and moves with it after impact). Impulse is a good way to do it.

And for those who think this is instant dead, I think you're wrong. There's only 2" of space under the thing. I don't know about you, but besides a very small part of my hand or wrist, my body's not going to fit in that space. So what happens? You get pushed, and it probably hurts a lot, since getting pushed at 6.5 MPH across asphault kinda sucks. But you're not going to die unless you're unlucky and get part of you caught under it.

-The Souljourner

 

[Christian]

Hmm. I think I was imagining it rolling, as if it were rolling on the highway rather than a few inches above it. That would pull the victim under and press him to a uniform thickness quite easily.

If it was just gliding, without rotation ... Well, it would depend on the shape, I think, and that's a much more difficult matter. If it were spherical, there would still be a 'wedging' effect on objects as it moved forward, which would result in substantial crushing damage (unless the road was very smooth and frictionless). A cube, with all faces parallel or perpendicular to the ground, might well just push someone along. Again, depending on the smoothness of the road, that could mean virtually no damage or a lot, but there wouldn't be a crushing effect because there's no room to even start forcing anyone underneath. A wedge, with a flat face parallel to the ground, and a gentle slope upwards on the top would have a very low probability of doing any damage at all-it would end up rolling the character up it and dumping them off the back or side. Lots of possibilities.

 

[chilibean]

How about this:

If you are in the path initially, you must make a reflex save of DC 15.

If you make it: you only take 1d6 impact damage and are forced to one side or the other.

If you fail: you take 1d6 impact damage and 2d6 dragging damage. You are moved 60' per round with the rock and must make a reflex save DC 20 to scramble out of the way. Failure means you take the 2d6 damage again and are moved 60' again the next round. Repeat until either you make it or are smeared into a red stain.

Allow another player with a move of at least 30, to run along with the rock and try to aid another if they wish. If they pass a DC 15 reflex save they can stay ahead of the boulder and can make a strength check of DC 10 (+1 per 20 lbs that the character and their gear weigh) to pull them free. If they fail their reflex save by more than 10 then they stumble and are now being dragged also. No impact damage but they take the 2d6 dragging damage as normal and they have to free themselves before they can help the other.

If they have a move of between 15 and 29 and want to try to aid someone being pushed, then give them a -1 to the reflex save and strength check for each movement point lower than 30 they have, since they have to be running harder just to stay ahead of the damn rock. A speed of lower than 15 would make it impossible (a double move run doesn't go as fast as the rock).

Is that reasonable?

 

[The Sigil]

Physics...

Ok, here some physics:

All calculations are done in metric system, for I'm from europe

Energy kinectic = .5*m*v^2
Energy gravity = m*g*h

An object weighting 200 pound (90 kg) does 1d6 points of damage if it falls over 10 ft. (3 mtr). The gravity acc is 9.81 m/s^2, in the netherlands
Egrav = 90 * 9.81 * 3 = 2648 J

So 2648 J is about 1d6 damage
The rest is calculatable with the first formula.
6.5 miles = 10.4 km/h = 2.89 m/s

The energy released would be: .5 * 45000 * 2.89^2 = 187922 J, or 71d6

As stated by others, this assumes that all energy is transferred to the victim... but when I saw this question, I thought of a different way of trying to figure it out that stays within D&D's abstract system (I think)...

Assumption:
Falling damage (from objects falling on characters, not characters falling to the ground) is essentially due to an object with a given mass smacking into the character at a given speed. In other words, I assume that if a character takes 1d6 hp of damage from a given object dropped from a height of ten feet, I can make some relations.

The object takes 0.791 seconds (g=32 ft/s^2=9.8 m/s^2) to fall from the release point to the character. At the time of impact, the object is moving at a speed of 25.3 ft/s (v=at).

Assumption:
An object moving at a given speed which hits a character from any direction, falling or not, inflicts the same amount of damage.

In other words, if an object inflicts 1d6 hp of damage by falling 10 feet onto my character (it is moving at 25.3 ft/s when it hits), it seems to me that if somebody threw the same object at my character horizontally (instead of vertically) at a rate of 25.3 ft/s, it would inflict 1d6 hp of damage, the same as though it had fallen on me.

F=ma, E=1/2 mv^2, and other strict physical equations for treatment of how Force/Energy are applied are not needed with these assumptions, all we need are the equations relating distance, velocity, acceleration, and time.

We can easily reverse-engineer the height from which the 50-ton object was dropped by calculating the time it would take for it to achieve the listed speed of 6.5 mph. 6.5 mph is equivalent to 9.53 ft/sec. Since v=at, and we know v (9.53 ft/s) and a (32 ft/s^2), we can find t (0.297 sec).

(This leads also to the consequence that since a round is 6 seconds long, the object has a move of ~60 feet... meaning that if the PCs run/sprint, moving 4xtheir base move, most medium-size PCs who are not too heavily encumbered should be able to beat this thing in a footrace... and a PC with no equipment should be able to move at least twice as fast as the object).

Now that we have the value of t, we can find the equivalent height from which it was dropped (d=0.5at^2)... the answer is 1.42 ft.

Now, I simply reference the SRD to see how much damage a 50-ton object does if dropped from a height of 1.42 feet... hmmm...

For each 200 pounds of an object’s weight, the object deals 1d6 points of damage, provided it falls at least 10 feet.

This tells me that I should prepare to do a freaking lot of damage... 50 tons comprises 500d6 points of damage...

But, we are given the caveat that the object must fall at least 10 feet, and our equivalent "fall" was only 1.42 feet.

Thus, by the rules, the 50 ton weight moving at 6.5 mph inflicts *no* damage (didn't fall far enough to "get started").

I would of course add a "common sense" corollary - a 50-ton weight smushes you up against something "immovable" (such as a wall), you get squished flat (dead), with a Ref save allowed to "get out of the way" first (a "save or die" situation).

Seems to me this is the simple way to handle it without trying to figure out exactly how many Joules of energy are in a d6... ;-)

--The Sigil

 

[nameless]

Analyzing the kinetic energy andwhatnot might tell you how much force the object has, but not necessarily how much d6 damage it inflicts. The system we have is 1d6 damage to a character per 10 feet fallen to the earth. This damage comes from the inelastic friction that the victim's body suffers when its momentum transfers to the earth. Basically, the fall isn't what hurts, it's the sudden stop at the end.

With a 100,000 lb. boulder compared to a 200 lb. adventurer, the boulder might as well be as massive as the earth, because its inertia is high enough that the adventurer cannot possibly affect it significantly (forget about superhuman strength and magic for a second. Secondary effects like being pinched between the boulder and another object, or being dragged aside, it's pretty accurate to consider it a fall at the end of which the victim is moving 6.5 mph relative to the earth... or the victim is running at a medium jog into a brick wall. Yes it hurts, but probably not more than a little bit of subdual damage, if any at all.

Now that I've given a long roundabout explanation, my ruling would be reflex save DC 10 to get out of the way, with the consequence of failing be 1d6 subdual damage, and being pushed along. If it was a rolling boulder, damage would probably be much higher, ditto for getting dragged beneath the object. I'd stick with very low damage for the initial impact, however.

-nameless

 

[Omegium]

Re: Physics...

Seems to me this is the simple way to handle it without trying to figure out exactly how many Joules of energy are in a d6... ;-)

--The Sigil

Well, I don't know if your way was really more simple, but it is fun to know how many joules there are in a d6. Now we can calculate how much water you can boil with a fireball, or how many fridges you need for a cone of cold