Gurps physics problems Mistborn power

[Enki]

good evening everyone, I have a problem with the physics of gurps about the possibility that a Demon can parry a trusting sword thrown through a psionic power point towards him at 540 Km/h.

Our characters are around 500 points at the end of the campaign. My power for those who know him is very similar to the "thrusts and throws" that develop in the book "mistborn" developped by telechinesis at level 36.

The situation is as follows: I fly over a demon with extremely hard skin and capable of changing it into bone.

the demon fights against another Pg and I use my "telekinetic" power at level 36 to push the 6 pound trusting sword against him. By rule the sword travels at 150 m/s or 164 yards/sec. or 540 km/h.

I wanted to use the rule on page 376 of the campaign: "Regardless of the weight of your weapon, if you are parrying unarmed or using a one-handed weapon, you cannot parry a weapon heavier than your Basic Lift -
or twice BL, if using a two-handed weapon.
attempts to parry anything heavier fail automatically; "

Calculation of the weight force of the moving sword on impact:
mass X ms / 0.1 (impact time)= 4.500 Newton or 458 Kg(force)

The master says that the demon can parry because the "weight" of the sword is 6 pounds. In addition, the demon parries with his hand transformed into a sword.

I point out that the impact force developed, given the speed at which it travels, is comparable to a 458 kg object that hits it from a meter.
definition of "Kg force"

He insists but in my opinion the correlation between "weight" and not "mass" is perfectly correct.

In addition, considering that we are less than 10 meters away the sword strikes in less than 0.1 seconds. How the hell does he fight with the other pg, turn around, position himself and parry?

The damage formula can be found on page 430 "An object in a collision inflicts crushing damage equal to [(HP X velocity) x2 hard object] / 100. "

total 46 damage dice.

Is it plausible that it can deflect such a shot without taking any damage?

has no penalty to parry a shot at 540 km / h from 10 meters?

Sorry if I went on, but gurps issues are worse than risiko games !.

[Refplace]

I'd use the Parry Missile Weapon rules.
However when talking about TK and magic you cant rely too much on real world physics, its a cinematic campaign at that point and no longer strictly realistic.

[malloyd]

Originally Posted by Enki

The master says that the demon can parry because the "weight" of the sword is 6 pounds. In addition, the demon parries with his hand transformed into a sword.

He is correct. Both because he's the GM, and by the rules as written. Parrying (and breakage) effects use the weight of the weapon, not a force of impact - which is always indeterminate anyway, because you don't know and have no real way of calculating how much distance (or time) the parry acts over. You've assumed it's 0.1 seconds for no apparent reason, but it's certainly much less than that for *any* weapon swing, which by your interpretation means you can basically never parry anything....

In any case by no means are the rules for melee combat any sort of physical model of anything. They're a playable rule set that gives you reasonable appearing results, not an effort to simulate the physics of colliding objects, which is extremely difficult to do and involves mathematics no sane game designer would consider using in a game. Indeed it tends to be so complicated and difficult that engineering where you actually need to know this stuff generally doesn't even *try* to calculate it, you really have to determine it experimentally.

[Mark Skarr]

Originally Posted by Enki

I wanted to use the rule on page 376 of the campaign: "Regardless of the weight of your weapon, if you are parrying unarmed or using a one-handed weapon, you cannot parry a weapon heavier than your Basic Lift -
or twice BL, if using a two-handed weapon.
attempts to parry anything heavier fail automatically; "

Calculation of the weight force of the moving sword on impact:
mass X ms / 0.1 (impact time)= 4.500 Newton or 458 Kg(force)

While the first part is part of GURPS the second is not.

Originally Posted by Enki

The master says that the demon can parry because the "weight" of the sword is 6 pounds. In addition, the demon parries with his hand transformed into a sword.

I would rule this way as well.

You are attempting to use a real-world interpretation, which is in violation of the spirit of the rule.

Originally Posted by Enki

He insists but in my opinion the correlation between "weight" and not "mass" is perfectly correct.

This is a game, not a Physics lesson/classroom.

Originally Posted by Enki

In addition, considering that we are less than 10 meters away the sword strikes in less than 0.1 seconds. How the hell does he fight with the other pg, turn around, position himself and parry?

How do you lift something telekintically? You're dealing with supernatural powers, don't think too hard on it.

Repeat to yourself: it's just a game, I should really just relax.

Originally Posted by Enki

The damage formula can be found on page 430 "An object in a collision inflicts crushing damage equal to [(HP X velocity) x2 hard object] / 100. "

total 46 damage dice.

And your GM would be justified in insisting that you cannot inflict 46d of damage, as you did not pay for a 46d attack.

Originally Posted by Enki

Is it plausible that it can deflect such a shot without taking any damage?

has no penalty to parry a shot at 540 km / h from 10 meters?

Sure, it's a game with supernatural elements. Anything is plausible.

[Enki]

Originally Posted by malloyd

He is correct. Both because he's the GM, and by the rules as written. Parrying (and breakage) effects use the weight of the weapon, not a force of impact - which is always indeterminate anyway, because you don't know and have no real way of calculating how much distance (or time) the parry acts over. You've assumed it's 0.1 seconds for no apparent reason, but it's certainly much less than that for *any* weapon swing, which by your interpretation means you can basically never parry anything....

ok is information extrapolated from real crash test data (0,1second).



In any case by no means are the rules for melee combat any sort of physical model of anything. They're a playable rule set that gives you reasonable appearing results, not an effort to simulate the physics of colliding objects, which is extremely difficult to do and involves mathematics no sane game designer would consider using in a game. Indeed it tends to be so complicated and difficult that engineering where you actually need to know this stuff generally doesn't even *try* to calculate it, you really have to determine it experimentally.

I'm perfectly agree with you. However, it seemed to me extremely reductive to use a parry skill without any modifier for the difficulty given the speed and impact power. it must be said that our master is "particular" and the same action on two different subjects leads to different results. I explain if they were the inverted parts I would not have been able to parry because the blow was too fast.

[Enki]

[QUOTE=Mark Skarr;2319141]While the first part is part of GURPS the second is not.




This is a game, not a Physics lesson/classroom.

I'm sorry our master teaches chemistry at university and physics use it when it suits him! XD

I don't argue. I just want to understand how certain things work to manage them

[Mark Skarr]

Originally Posted by Enki

I'm sorry our master teaches chemistry at university and physics use it when it suits him! XD

I don't argue. I just want to understand how certain things work to manage them

Aha! Fair enough. Good to know.

Then tell your GM:
"This is just a game, I should really just relax."

[Anaraxes]

Well, we're talking about using superpowers energized by magic fueled by consuming specific types of metals to attack a demon. So, I wouldn't get too hung up on "physics" or "realism".

Where do you get the 164 yards/sec number? RAW gives objects moved by TK a Move equal to the TK level (so, here, 36, which is 36 yds / s. (If you prefer metric units, the easy thing to do is just read "yards" as "meters", rather than try to do exact conversions. The difference isn't going to break anything.)

(Depending on how fast your Flight ability is, it's entirely possible you couldn't TK something along as fast as you could fly. In that case, you'd have to carry in physically rather than tow it along to ram some unfortunate demon on the ground at your flight speed. You also have to Concentrate to maintain TK, which would make it hard to do a full Move, absent other abilities and modifiers. Rather than TK-ing yourself to fly with the TK rules, it's probably better just to buy Flight as an Alternate Ability with the TK.)

An attack is presumably using the "Throw" subsection of TK, which just treats TK as ST. Throwing doesn't have any specified speed that I recall. (Neither do bullets. All direct attacks hit on the turn on which they're made, regardless of distance or projectile velocity. It's occasionally pointed out that this is untrue for long-range rifle attacks -- but there aren't any rules for time-of-flight of attacks as far as I know.)

The parrying heavy weapons rules are meant as a simple rule-of-thumb to incorporate problems stopping heavy giant clubs with your tiny pixie dagger. Again, i wouldn't try to drag kinetic energy or momentum calculations into it. That's not where those numbers come from in the first place. There have been some past houserule discussions to use attacker ST as a factor in the "ability to parry" comparison rather than just weight. If you liked one of those, you might use the TK strength in that rule.

Parries are normally allowed to parry thrown weapons. So, if the sword is being "thrown" with TK, it can be parried (by RAW), just as if it were thrown by hand. (Wielding the sword to attack with TK isn't the same as throwing the sword.) Missile weapons can't be parried -- unless the demon has the Parry Missile Weapons skill. Or if the game is just that cinematic that that's just a campaign rule, which isn't unlike given that's it's Mistborn.

I don't think RAW specifies any particular velocity number dividing "thrown" from "missile" weapons. Your 150 m/s lies in between real-world arrow velocities and bullet velocities (closer to arrows), so if that were the desired criteria, then this "thrown" sword would presumably be classed as a "missile" weapon for parrying purposes.

[Enki]

Originally Posted by Anaraxes

Well, we're talking about using superpowers energized by magic fueled by consuming specific types of metals to attack a demon. So, I wouldn't get too hung up on "physics" or "realism".

Where do you get the 164 yards/sec number? RAW gives objects moved by TK a Move equal to the TK level (so, here, 36, which is 36 yds / s. (If you prefer metric units, the easy thing to do is just read "yards" as "meters", rather than try to do exact conversions. The difference isn't going to break anything.)

(Depending on how fast your Flight ability is, it's entirely possible you couldn't TK something along as fast as you could fly. In that case, you'd have to carry in physically rather than tow it along to ram some unfortunate demon on the ground at your flight speed. You also have to Concentrate to maintain TK, which would make it hard to do a full Move, absent other abilities and modifiers. Rather than TK-ing yourself to fly with the TK rules, it's probably better just to buy Flight as an Alternate Ability with the TK.)

An attack is presumably using the "Throw" subsection of TK, which just treats TK as ST. Throwing doesn't have any specified speed that I recall. (Neither do bullets. All direct attacks hit on the turn on which they're made, regardless of distance or projectile velocity. It's occasionally pointed out that this is untrue for long-range rifle attacks -- but there aren't any rules for time-of-flight of attacks as far as I know.)

The parrying heavy weapons rules are meant as a simple rule-of-thumb to incorporate problems stopping heavy giant clubs with your tiny pixie dagger. Again, i wouldn't try to drag kinetic energy or momentum calculations into it. That's not where those numbers come from in the first place.

Parries are allowed to parry thrown weapons. So, if the sword is being TK-thrown, it can be parried (by RAW). Missile weapons can't be parried -- unless the demon has the Parry Missile Weapons skill. Or if the game is just that cinematic that that's just a campaign rule, which isn't unlike given that's it's Mistborn.

I don't think RAW specifies any particular velocity number dividing "thrown" from "missile" weapons. Your 150 m/s lies in between real-world arrow velocities and bullet velocities (closer to arrows), so if that were the desired criteria, then this "thrown" sword would presumably be classed as a "missile" weapon for parrying purposes.

i perfectly understand what you write and confirm it. However the GM shortly before told me that if it had been a gun bullet he could not have parry because he would not have had the time. Faced with the famous metric conversions of speed, to which I compared bullet and sword he said "that is a sword not a bullet" XD

[Enki]

anyway thank you you have been very exhaustive.

One must be patient and remember that it is only a pleasant pastime.