Falling off a moving train, impact speed for falling dam?

[Ultraviolet]

Ok people

The ongoing Cliffhangers campaign is going to feature an adventure involving a rain, and of course there will be fighting on top.

We're talking late 20's China, to train speeds are not impressive. No offense, but it fits the plot best if they aren't too fast.

So, what do you do for distance and speed, when calculating impact speed for falling damage? A character falling off is initially traveling at the speed of the train, but wind resistance etc means they should slow down. And the there is the height from the top of train carriage to the ground, because naturally the tracks are built on a dirt bank raised above the terrain. That's not going to be more than 5 yards total.

So, should I just use the speed of he train? I'm going for 9 yds/sec.
Should I add the speed calculated from the falling distance to this speed? For 5 yards fall that's a velocity of 10, which would almost double the damage from falling off this slow train.

Did anyone else ever find themselves in this situation?

[coronatiger]

Air resistance won't reduce the forward velocity noticeably in the time it takes to fall to the ground. You could use Pythagoras to find the impact velocity, with the train's speed and the speed at the end of the fall (from the table in Campaigns) as the sides of the triangle. This won't affect the impact damage much if either speed is much greater than the other.

[Tomsdad]

Originally Posted by Ultraviolet

Ok people

The ongoing Cliffhangers campaign is going to feature an adventure involving a rain, and of course there will be fighting on top.

We're talking late 20's China, to train speeds are not impressive. No offense, but it fits the plot best if they aren't too fast.

So, what do you do for distance and speed, when calculating impact speed for falling damage? A character falling off is initially traveling at the speed of the train, but wind resistance etc means they should slow down. And the there is the height from the top of train carriage to the ground, because naturally the tracks are built on a dirt bank raised above the terrain. That's not going to be more than 5 yards total.

So, should I just use the speed of he train? I'm going for 9 yds/sec.
Should I add the speed calculated from the falling distance to this speed? For 5 yards fall that's a velocity of 10, which would almost double the damage from falling off this slow train.

Did anyone else ever find themselves in this situation?

Assuming there isn't an obstacle their sideways movement will slam them into the side of before hitting the ground, but rather they're going to hit the ground and then bounce along until stopping.

My compromise would be add half the lowest of either speed to the total of the highest of either speed. So in this case you end up hitting with a velocity of 14 or 15 depending on how you round.

No idea if that is correct by the laws of physics, but to me it seems a reasonable compromise and would meet my GM on the fly criteria of "pleasingly worse, without being instant death and looks to be in the ball park of being right"


An easier and more lenient option would be just to take the fastest velocity and base damage off that. I.e. if the Horizonal velocity is greater than the vertical use that, or if the vertical velocity is greater use that.

This might be too lenient for realism but might work well for a cliff hangers game.

[GodBeastX]

My initial gut reaction is to take the distance to the ground as falling injury. After figuring for that I'd follow rules for collision if the person impacts with an unyielding object in the forward motion as separate injury.

You could maybe make some sort of skill check to see if they brace for a "Roll" correctly to mitigate injury of forward rolling (I always like dice rolls for stuff like this, keeps people on their seat!)

Otherwise Maybe add some extra injury if the speed is too great to handle ragdoll and body rotating over a hard surface. This could increase if the ground is notably jagged. Another die or maybe +1/+2 per dice on the forward motion?

The reason I'd handle them separately is that there is no sudden stop on the forward motion. 9y/s doesn't seem right to add to the fall damage.

[Stormcrow]

Surely this is an example of a side-on collision or fall (page B432)? I imagine that even on a relatively slow-moving train, say, 40 mph or about 20 yards per second, the train's velocity is much greater than the vertical velocity of the fall itself. As a side-on collision or fall, you use the velocity of the striking or falling object. In the case of our 40 mph train, if we suppose a 10 HP man falling off onto hard ground, that's 2 × (10 × 20)/100 = 4 dice of damage.

[GodBeastX]

Originally Posted by Stormcrow

Surely this is an example of a side-on collision or fall (page B432)? I imagine that even on a relatively slow-moving train, say, 40 mph or about 20 yards per second, the train's velocity is much greater than the vertical velocity of the fall itself. As a side-on collision or fall, you use the velocity of the striking or falling object. In the case of our 40 mph train, if we suppose a 10 HP man falling off onto hard ground, that's 2 × (10 × 20)/100 = 4 dice of damage.

This could possibly be a side on collision but the x2 multiplier confuses me. Why is it doubling the impact?

[Anthony]

In this case I would probably just use the fall distance; the train's sideways velocity mostly translates to skidding which isn't going to be super dangerous unless you happen to skid into a rock.

[MrFix]

Suprisingly, GURPS has rules for falling out of a vehicle. B468, "Bailing Out of a Moving Vehicle".
The damage they would suffer is... 10 velocity from falling, 9 velocity from moving train, 19 y/s velocity. x2 for impact with immovable object (the earth). Assuming 10 HP...

(2x10x19)/100=3.8d, or 4d crushing. Roll for a hit location too, to allow breaking a leg, see box on B431.

[Stormcrow]

Originally Posted by GodBeastX

This could possibly be a side on collision but the x2 multiplier confuses me. Why is it doubling the impact?

Because the ground is an immovable object, and collisions with hard immovable objects like clay and soil count double the HP of the moving object (page B431).

Originally Posted by MrFix

Suprisingly, GURPS has rules for falling out of a vehicle. B468, "Bailing Out of a Moving Vehicle".

Ah! I got it right. (I missed the desired velocity of 9 in the original post.) You just use the velocity of the moving object.

A 10 HP person landing on soil: [10 HP]× [2 for hard] × [9 velocity] / 100 = 1.8. I think you're supposed to round down this calculation, since it's not a character point cost, so that's 1d of damage.

The damage they would suffer is... 10 velocity from falling, 9 velocity from moving train, 19 y/s velocity. x2 for impact with immovable object (the earth). Assuming 10 HP...

(2x10x19)/100=3.8d, or 4d crushing. Roll for a hit location too, to allow breaking a leg, see box on B431.

You only add falling damage if you're bailing out of an aircraft (and even then, you don't add velocities, only damage dice). 4d for only falling off a vehicle moving 18 mph is obviously excessive.

[Plane]

Originally Posted by Anthony

In this case I would probably just use the fall distance; the train's sideways velocity mostly translates to skidding which isn't going to be super dangerous unless you happen to skid into a rock.

I wouldn't want to take a 6-inch fall with 100mph of momentum that the ground lacks and wants to decelerate if that ground had a lot of thorns or pebbles unless I had some kind of leather jacket.

There are rules for decelerating when it happens faster than your Basic Move, can we use them here? If you don't do it properly then you fall. If you don't try to decelerate then you'll make a different DX check which can also cause a fall.

But "falling when you are already lying on the ground" is weird: there's no height.

Unless we use bounces: maybe the collision damage that ground does to you should inflict knockback, and then you can suffer more falls from that knockback.

Only diff is clearly you need something other than Roll With Blow which doubles knockback because that doesn't make sense with a bounce into the air (doubling height). RWB's increase is because you're jumping back with the hit, because you're already on the ground able to push off it. That's not really possible when the ground itself is the enemy, more like if you had some wall near the ground to kick off to decelerate off.

"rolling" if not damaging should be disorienting in some way.