ultimate combat armor dr terrible?

[nihil8r]

anyone else think the new pathfinder rules for armor dr in place of armor ac are atrocious? (on page 191 of ultimate combat). creatures larger than you can bypass your dr just because they're larger than you, and YOU make critical confirmation rolls rather than your attacker? lolwut? i think armor dr is a great idea but seriously . . . tell me again why being larger bypasses armor? because last time i punched a baby wearing armor, the armor still protected it.

[awa]

well i don't have ultimate combat so i haven't seen the rules but even the heaviest armor in the world wont protect you from an elephant stepping on you that's likely the the logic. (of course on the other hand that should probably be represented by the elephant doing a lot of damage)

[nihil8r]

right, a crushing attack that does massive damage is not the same as ignoring armor altogether ... being one size category larger doesn't make steel plates go away. :smallfurious::smallfurious::smallfurious:

[Duncan_Ruadrik]

i didn't find the rules BAD, per se, just very, very clunky, to the point of being useless. I mean, WOTC had an armor class as DR that at least worked relatively well, especially in low magic settings. but Pathfinder's reinterpretation... made me shudder a bit.

[mootoall]

Is armor as DR in the 3.5 SRD? If so, they should've just used that, since it's usable under the d20 license.

[Togath]

Aye, the 3.5 armor as DR is ogc, Also it's fairly balanced(armor still provides an armor boost, but only about half of its standard amount, and you gain the other half as DR that stacks with all other sources of DR)

[Tetrasodium]

It looks a little on the ugly side right now, but I think there are a couple reasons it might turn out situationally ok. I've seen posts on the paizo forums referencing past official forum/blog/etc comments that suggest expanding things towards higher levels is a goal in the next year or so, combined with some of the new classes and potential newer ones by then, it could possibly be one of those things you switch to at higher levels to eradicate some of the flaws present in 3.5's high/epic level play. Heck I could imagine it doing great in a pathfinder DDO style game where you have ridiculous 80+ AC type tank builds tanking mobs that everyone else might as well be naked to... and they still haven't really gotten into epic play yet. I joined up with a group once that expected that sort of thing against his monsters*

*You know your #%^@'d when the GM shows you a dragon out of a shadowrun book he seems to be using for it's attacks and such... and then he pulls out a Rifts book for its backup reinforcements when the group manages to survive simply by virtue of the gestalt wizard/warforged juggernaut being immune to damn near everything that took everyone else out of the battle. Yes it was a terrible game on top of being gestalt in a version of gestalt even worse than normal gestalt (make 2 level 20 characters and next session he tells everyone to merge our characters with the gear from both so the wizard's 20+int replaces the juggernaut's <10ish int and vice versa with everything... skills/feats/stats/hp/etc)

[Knaight]

right, a crushing attack that does massive damage is not the same as ignoring armor altogether ... being one size category larger doesn't make steel plates go away. :smallfurious::smallfurious::smallfurious:

If a truck hits you, it doesn't matter what armor you are wearing. Armor doesn't reduce the amount of force applied to one when they are struck, it merely increases the area through which that force is applied (and the mass to which it is applied). That works beautifully against things your size, but as things get bigger, and sheer force starts mattering much more than pressure it goes away. That is actually sensible.

Now, there is the matter of the specifics of how it was designed. I'm not going to comment on that.

[Drachasor]

If a truck hits you, it doesn't matter what armor you are wearing. Armor doesn't reduce the amount of force applied to one when they are struck, it merely increases the area through which that force is applied (and the mass to which it is applied). That works beautifully against things your size, but as things get bigger, and sheer force starts mattering much more than pressure it goes away. That is actually sensible.

By that same reasoning, you get hit by something like that, then you should be dead. It doesn't matter who you are, how many levels you have, or how many hit points, getting hit by a truck or stomped by a giant's club (which is bigger than you) is going to kill you.

Rules like that are made by people who haven't realized this is a fantasy game with a lot of inherently unrealistic things in it. Hence they make rules which seem to be about how non-magic-users are not allowed to have nice things.

Oh, and by the way, armor WILL reduce the impact of a truck hitting you. It's just that in real life a truck is OVERKILL and so will kill you anyways. A truck doesn't evenly spread its force over your body. You're going to get hit at discrete points because neither you nor the truck are flat surfaces. Armor will lessen that impact, and also the fact that the armor will get crushed will further lessen the impact, absorbing energy (this latter principle is used with cars themselves, which is why the fronts and backs readily get smooshed in impacts, to absorb the blow for the passengers).

Well, obviously PF cares more about keeping casters powerful than about balance. *sigh*

[Blisstake]

Well, I think there's a reason this is an optional rule. If you're arguing realism, however, I don't either system is a very accurate representation of how combat would work - they're just two different ways to try to express what armor's effect in combat would be.

In a gameplay perspective... no comment.

[nihil8r]

let me break down further what the problem is. if a large-size ogre attacks you, your armor (according to these rules) doesn't count.

whut?

this has absolutely no real-world correlation to the fact that being hit by a truck at highway speeds is fatal. large-size weapons ALREADY have increased damage because they are bigger. with these new "rules," simply being bigger by a couple of feet is enough to ignore mundane armor for no reason whatsoever. so a larger size creature not only gets its bonus damage for using a larger weapon, it ALSO gets to now ignore your armor reduction because it is a few feet bigger.

i'm a big fan of the core pathfinder book and especially the pathfinder dmg, but ... the whole point of buying rpg books is to get access to materials that are BETTER than material that you could come up with yourself while drunk.

incidentally, the house rules i made for bone/bronze/stone/etc are much better than pathfinder's so ... with this book i feel i basically paid $40 for the ninja class one of my players wanted. awesome.

[Drachasor]

Well, I think there's a reason this is an optional rule. If you're arguing realism, however, I don't either system is a very accurate representation of how combat would work - they're just two different ways to try to express what armor's effect in combat would be.

In a gameplay perspective... no comment.

Doesn't the gameplay perspective matter? It's an optional rule for a game...and as a game rule, it sucks.

[Knaight]

By that same reasoning, you get hit by something like that, then you should be dead. It doesn't matter who you are, how many levels you have, or how many hit points, getting hit by a truck or stomped by a giant's club (which is bigger than you) is going to kill you.

Only if you get hit head on. Its just that armor is nearly useless, and what matters if you get hit is the extent to which you get hit. A graze of some sort, that pushes you aside while it keeps moving? You might well be fine.

Now, one size difference completely removing armor is bull. But if it were three size categories, there would be absolutely no issue. Plus, designed well, this would actually provide an incentive not to wear armor, and thus create the sort of world where certain lightly armored archetypes work well. Of course, rules designed well wouldn't have the whole gigantic caster noncaster disparity to begin with, unless it was a case like Ars Magica where it fits and is deliberate.

[Blisstake]

Doesn't the gameplay perspective matter? It's an optional rule for a game...and as a game rule, it sucks.

It does. I haven't had the time to analyze it, and it seemed the OP was arguing more for realism than gameplay effect.

[Drachasor]

Only if you get hit head on. Its just that armor is nearly useless, and what matters if you get hit is the extent to which you get hit. A graze of some sort, that pushes you aside while it keeps moving? You might well be fine.

It doesn't matter if you get hit in the head, side, leg, or whatever. If you get hit by something moving at a high speed, even if it just grazes you the change in your angular velocity will be such that you'll hit something and die. For example: Leg gets nicked by a truck moving at high speed? spins your whole body around and your head smashes into the truck. A Huge-sized giant's club isn't going to go any better for you.

Even if you ignore that, aren't slight hits handled better by DR than AC? The latter is a binary system. DR just makes it a little more likely that you'll get a light hit, whereas an AC increase makes it more likely you won't get hit at all (somehow). So DR is actually superior for getting hit by big things, since really big hits won't be impacted by DR that much, but are still impacted greatly by AC (which can easily cause them to flat-out miss).


Now, one size difference completely removing armor is bull. But if it were three size categories, there would be absolutely no issue. Plus, designed well, this would actually provide an incentive not to wear armor, and thus create the sort of world where certain lightly armored archetypes work well. Of course, rules designed well wouldn't have the whole gigantic caster noncaster disparity to begin with, unless it was a case like Ars Magica where it fits and is deliberate.

First, armor will still provide protection even against big things. Like I said above before.

Second, Huge hits are represented as dealing more base damage, which the game already does. Moreover more base damage already makes DR less meaningful. DR wonderfully handles it, so there's no reason to just toss the DR aside. Against a something dealing 40 damage on a hit, 5 DR is not going to be that great, better to not get hit at all. This is just an unnecessarily (and unrealistic within the setting) harsh penalty on armor wearers who would already be penalized fighting such creatures.

In the DR-world, people in light armor already have an inherent advantage. They get a bit of DR against light hits, and a higher AC to avoid a lot more hits (we're assuming they have high dex, otherwise they'd wear heavy armor). Removing DR against big creatures gives them even more of an advantage.

So exactly how does is this system not a failure? Within the bounds of a fantasy setting it is not realistic. Within the bounds of gameplay it unfairly punishes a valid playstyle (people wearing heavy armor).

[Knaight]

It doesn't matter if you get hit in the head, side, leg, or whatever. If you get hit by something moving at a high speed, even if it just grazes you the change in your angular velocity will be such that you'll hit something and die. For example: Leg gets nicked by a truck moving at high speed? spins your whole body around and your head smashes into the truck. A Huge-sized giant's club isn't going to go any better for you.
Sure, if your entire leg gets nicked there will be issues. However, that doesn't mean there aren't grazes. The human body isn't entirely a single, discrete object, so its not just a matter of angular velocity. A car that hits someone ever so barely along the side of an arm will jerk them around, but the energy will also go into deforming the part of the arm struck, and probably taking off a small chunk of arm. It is, however survivable, as the numerous accounts of people grazed by even large trucks documents, though "survivable" by no means is an indication that there is no injury, or even no major injury.


First, armor will still provide protection even against big things. Like I said above before.

Nonmagical armor in D&D provides from 1 to 8 points of AC. In a system with 8 levels of armor, there isn't sufficient detail for the extent to which armor protects against, say, getting hit by a truck to actually be worth counting.

[Urpriest]

Large creatures still deal their damage via precision, not simply by squashing people. Hence the ability of creatures of any size to deal sneak attack damage.

[Tebryn]

Doesn't the gameplay perspective matter? It's an optional rule for a game...and as a game rule, it sucks.

The don't use it?

[Drachasor]

The don't use it?

Well, why sell a book with bad rule ideas in it? Aren't customers paying for GOOD ideas?


Sure, if your entire leg gets nicked there will be issues. However, that doesn't mean there aren't grazes. The human body isn't entirely a single, discrete object, so its not just a matter of angular velocity. A car that hits someone ever so barely along the side of an arm will jerk them around, but the energy will also go into deforming the part of the arm struck, and probably taking off a small chunk of arm. It is, however survivable, as the numerous accounts of people grazed by even large trucks documents, though "survivable" by no means is an indication that there is no injury, or even no major injury.

Well, I'm thinking semis on the highway here. Part of my point is that hits like that ARE survivable in D&D...because it's a fantasy game. Trying to pin too much stuff to what is "realistic" in our world is ridiculous, because there are a dozen things non-magical D&D characters do that are impossible for us.


Nonmagical armor in D&D provides from 1 to 8 points of AC. In a system with 8 levels of armor, there isn't sufficient detail for the extent to which armor protects against, say, getting hit by a truck to actually be worth counting.

And the DR is going to matter all that much? There's no good reason to say the DR should be ignored. It's bad game design, bad fantasy reality, and just bad in general.

You know, with your reasoning, might as well say there's no reason to pay attention to armor at all. It's the same level of abstraction with a big hit verses a small hit.


Large creatures still deal their damage via precision, not simply by squashing people. Hence the ability of creatures of any size to deal sneak attack damage.

Technically, I'm not so sure.

"The rogue must be able to see the target well enough to pick out a vital spot and must be able to reach such a spot. A rogue cannot sneak attack while striking a creature with concealment."

So how exactly does something where even a single one of its fangs is the size of a man's head pick out a vital spot and reach it? Kind of arguable that they can't target it anymore than a rogue can sneak attack something he can only reach the heals of.

Besides the point though.

[Greenish]

Aren't customers paying for GOOD ideas?Signs point to "no". :smallamused:

The third edition continuum has more than it's fair share of poor ideas, yet the books continue to sell. UA's "armour as DR" system only works on low levels, for example.

[Knaight]

You know, with your reasoning, might as well say there's no reason to pay attention to armor at all. It's the same level of abstraction with a big hit verses a small hit.

In situations where one combatant is so much bigger than the other, that any real hit is likely to kill them, ignoring armor makes perfect sense. In situations where the sizes are close enough for armor to actually be protective sensibly, it doesn't.

Moreover, even if you make hits that should kill survivable, with the standard fantasy throw on top of that, armor is still nonsensical as a protective mechanism in most cases. So yes, I'm all for not paying attention to armor where it is largely irrelevant. I'm also for not paying attention to what people ate for breakfast the morning before the fight, if people are likely to be tired because they had a strenuous argument before they slept, or any number of factors that are, frankly, either boring or irrelevant at the scale involved.

[Drachasor]

Signs point to "no". :smallamused:

The third edition continuum has more than it's fair share of poor ideas, yet the books continue to sell. UA's "armour as DR" system only works on low levels, for example.

Well played, Greenish, well played.


In situations where one combatant is so much bigger than the other, that any real hit is likely to kill them, ignoring armor makes perfect sense. In situations where the sizes are close enough for armor to actually be protective sensibly, it doesn't.

Dinky DR doesn't matter there, so making specialized rules for it doesn't make sense. It's bad game design to have needlessly complicated rules. Also, there's no reason the armor would still provide protection -- it's just that the protection isn't enough.



Moreover, even if you make hits that should kill survivable, with the standard fantasy throw on top of that, armor is still nonsensical as a protective mechanism in most cases. So yes, I'm all for not paying attention to armor where it is largely irrelevant. I'm also for not paying attention to what people ate for breakfast the morning before the fight, if people are likely to be tired because they had a strenuous argument before they slept, or any number of factors that are, frankly, either boring or irrelevant at the scale involved.

Paying attention to armor is something you do all the time anyway. Not doing it is a special case, which complicates gameplay (you already have to pay attention to the hit anyhow). Special cases are best avoided... especially when they provide little to no value. Armor as DR applying in some circumstances but not others is a perfect example of this.

[Knaight]

Dinky DR doesn't matter there, so making specialized rules for it doesn't make sense. It's bad game design to have needlessly complicated rules. Also, there's no reason the armor would still provide protection -- it's just that the protection isn't enough.




Paying attention to armor is something you do all the time anyway. Not doing it is a special case, which complicates gameplay (you already have to pay attention to the hit anyhow). Special cases are best avoided... especially when they provide little to no value. Armor as DR applying in some circumstances but not others is a perfect example of this.

Ah, I see where we went wrong here. The first post was complaining from realism issues, and I'm talking from basic theory. You are assuming a D&D base, and within the known rising damage, the fact that DR gets piddly anyways, so on and so forth, I agree that the specialized rules aren't good design. I maintain, however, that scaling armor effectiveness rules with size, from a base closer to AC makes perfect sense, and isn't necessarily complicated.

[Zeta Kai]

So a larger size creature not only gets its bonus damage for using a larger weapon, it ALSO gets to now ignore your armor reduction because it is a few feet bigger.

Not to mention that the weapon that they are hitting you with is still smaller than you. It may be big, but that ogre's club is big like "a fire hydrant", not big like "another guy in armor".

[Drachasor]

Ah, I see where we went wrong here. The first post was complaining from realism issues, and I'm talking from basic theory. You are assuming a D&D base, and within the known rising damage, the fact that DR gets piddly anyways, so on and so forth, I agree that the specialized rules aren't good design. I maintain, however, that scaling armor effectiveness rules with size, from a base closer to AC makes perfect sense, and isn't necessarily complicated.

Well of course I'm assuming a D&D base in the D&D forum. That makes sense, right?

I think in D&D scaling armor bonuses with the size of the opponent is pretty complicated. It's like the armor optional rules in 2nd Edition, where chain mail was better against say slashing weapons and weaker against piercing weapons (and so forth for other armor types). It amounts to a lot to keep track of. So while AC might reflect real world armor well in a number of ways, I think DR is theoretically a better system in terms of actual play. Assuming one is highly concerned about balancing realism with ease of play.

Though, with another system that works differently, scaling things with size might not be cumbersome. I'd have to see the system first before I could say.

[Arbane]

Well, I'm disappointed. I assumed this thread would be about some mad scientist named Doctor Terrible, and his ultimate suit of combat armor.

Oh, well.

[Psyren]

Well, I'm disappointed. I assumed this thread would be about some mad scientist named Doctor Terrible, and his ultimate suit of combat armor.

Oh, well.

That joke was Dr. Terrible :smalltongue:


Signs point to "no". :smallamused:

The third edition continuum has more than it's fair share of poor ideas, yet the books continue to sell. UA's "armour as DR" system only works on low levels, for example.

To be fair, regular armor-based AC only works at low levels too.

I agree that this version sucks though and hope they errata it. But pretty much the only folks actually getting my PF dollar are Dreamscarred Press, I'll crib everything else from the SRD.

[Knaight]

Well of course I'm assuming a D&D base in the D&D forum. That makes sense, right?

Not when the first post is about realism, and overly wide claims regarding universality have been made. After all, consider some of the other d20 games which are technically encompassed in this forum. M&M for instance, or what The Far West is probably going to look like.

[Tetrasodium]

I reread the thing, truth be told I only kinda glanced at it before when I first got UC. I ha two things to say abut it though... The first is that it's needlessly complicated when it goes from just dr/armor to dr/ooh it depends onsize & existing DR and you get one of lots of easily defeated /types that seem highly arbitrary & I'm not sure what that adds to the system. The second is that I think it shows real potential for epic levels if combined an addition where armor can somehow continue to get better and better beyond the simple +5 whatever armor with the usual dex cap and base armor bonus. opponents are still able to hit each other due to the DS=10+dex od+shield bonus=[deflection+luck bonus ac+etc] for traditional AC's role, but a progression of armor getting better st epic levels would allow things to not brea down as badly as 3.5 when it comes to epic levels. Truth be told, it would probably take a lot of changes in general to work.

[ShneekeyTheLost]

Only if you get hit head on. Its just that armor is nearly useless, and what matters if you get hit is the extent to which you get hit. A graze of some sort, that pushes you aside while it keeps moving? You might well be fine. Actually, not true. Wearing armor can make you get launched instead of gibbed.

You see, there's an annoying little problem with kenetic energy transference. Since you've got nothing bracing you, when a large object hits you, it tens to make you go flying. And that whole 'going flying' bit is what steals much of the kenetic energy supposedly being transferred.

In other words, getting hit by a vehicle is very likely to do very little actual damage to a person in rigid metal armor, due to being able to transfer energy around you, much like being grounded while a current is going around you. Flexible armor, however, doesn't do a hell of a lot. Plate helps a hell of a lot more than chain against massive blunt force trauma.

In fact, given the relative heights involved, wearing full plate and getting hit by a car is going to end up in you getting flipped arse-over-teakettle, rolling up the windshield of the vehicle, and probably either dumped over the side or over and off the backend, depending on the vector of impact and your movements while airborne. Depending on the padding of said full plate, you might get out of it with nothing more than dented armor.

Saw this happen at an SCA event once, even if it was by accident. Funny as hell to see a guy in full plate get hit, only to brush himself off and saunder on his merry way while the owner of the vehicle had to call a tow truck.

[Tetrasodium]

Actually, not true. Wearing armor can make you get launched instead of gibbed.

He is, just not for the right reasons.Humans have all sorts of important gooey bts inside them If you ever had to make a box that protects an egg from a drop off a building in school* , you'd remember that there's more than just stopping the egg from hitting the ground. You need to keep it fr being destroyed when the ground suddenly causes a rapid deceleration. Armor has similar with acceleration because of your gooey bits. Just because the armor protects you from the blow, doesn't mean it protects you from the kinetic force of the armor hitting you and screwing up all those internal gooey bits ;)

*you have to be able to remove the egg without breaking it so filling the no with foam won't work unless you can easily dissolve the foam without harming the egg. If the egg survives, it gets broken to be sure wasn't killed before the drop (hard boiled/frozen).

[ShneekeyTheLost]

He is, just not for the right reasons.Humans have all sorts of important gooey bts inside them If you ever had to make a box that protects an egg from a drop off a building in school* , you'd remember that there's more than just stopping the egg from hitting the ground. You need to keep it fr being destroyed when the ground suddenly causes a rapid deceleration. Armor has similar with acceleration because of your gooey bits. Just because the armor protects you from the blow, doesn't mean it protects you from the kinetic force of the armor hitting you and screwing up all those internal gooey bits ;)

*you have to be able to remove the egg without breaking it so filling the no with foam won't work unless you can easily dissolve the foam without harming the egg. If the egg survives, it gets broken to be sure wasn't killed before the drop (hard boiled/frozen).

Not the same at all, and here's why:

For every action, there's an equal and opposite reaction. That's why the egg goes splat... not because it's moving at terminal velocity, but because the ground hits the egg as hard as the egg hits the ground. Needless to say, the ground wins, since the kenetic energy going into the egg has nowhere to go BUT the egg.

However.

When a person in rigid armor is broadsided by a vehicle, however, the entirety of the kenetic energy is not transferred into the individual. Namely, it's not the person being hit, it's the rigid armor. Also of important note is that the maximum amount of force that can be applied is the amount of force necessary to move the person in the suit of armor out of the way. Excess kenetic energy is completely wasted and harmlessly applied at the air behind him, which of course compresses and decompresses rather easily.

So Mr. Suit of armor gets launched sideways. The suit of armor is dented by initial impact, and probably dented again when the back impacts against the ground, although probably not because the angle of impact is acute enough that he skips along rather than having the entirety of the kenetic energy bleed off while skidding along the side of the road, rather than impacting and coming to a dead stop instantly (which probably WOULD kill the inhabitant).

This is the same phenomenon which makes an impact with a sapling much more survivable than an impact with a brick wall. You run over the sapling, and come to a halt, but much of the kenetic energy bled off, since you only had as much kenetic energy coming back as was necessary to knock down the sapling and roll over it. The brick wall, on the other hand, stops you dead, the entirety of the kenetic energy goes back through the car, and you'd better have your seat belt on and an airbag if you want to survive the return shock.

Oh, it's easy to make the egg survive the fall, by the way. You build a harness with springs attached to it to go inside the box. When box lands, spring coils, redirecting kenetic energy into the harness. It may bounce a couple of times, but the egg is all nice and safe.

Next time, try pedantry with someone other than an engineer, mmmkay?

[Tetrasodium]

For every action, there's an equal and opposite reaction. That's why the egg goes splat... not because it's moving at terminal velocity, but because the ground hits the egg as hard as the egg hits the ground. Needless to say, the ground wins, since the kenetic energy going into the egg has nowhere to go BUT the egg.

Next time, try pedantry with someone other than an engineer, mmmkay?

Cute... but you fail and miss the important bit about those gooey bits we all have.. you fail (http://en.wikipedia.org/wiki/Dementia_pugilistica), and ultrafail (http://www.usatoday.com/news/nation/2005-03-03-brain-trauma-lede_x.htm) with actual armor this time...
"A growing number of U.S. troops whose body armor helped them survive bomb and rocket attacks are suffering brain damage as a result of the blasts. It's a type of injury some military doctors say has become the signature wound of the Iraq war"
Armor protects the body sure... but not the gooey bits inside. It's a similar reason to why they always try to convince you to go to the ER when you have an accident and thanks to the protection of your seatbelt/airbag/etc "feel fine"
Ad to the rigid armor gets hit, not the wearer bit... the wearer gets hit by the armor unless hat armor is capable of completely absorbing the entire blow and transferring the kinetic energy into something else (like a springy support structure)... but since armor you can't move is called a fortress rather than armor... lets stick with armor you can move around the world in without an external support structure like gets used in d&d

[Drachasor]

Cute... but you fail and miss the important bit about those gooey bits we all have.. you fail (http://en.wikipedia.org/wiki/Dementia_pugilistica), and ultrafail (http://www.usatoday.com/news/nation/2005-03-03-brain-trauma-lede_x.htm) with actual armor this time...
"A growing number of U.S. troops whose body armor helped them survive bomb and rocket attacks are suffering brain damage as a result of the blasts. It's a type of injury some military doctors say has become the signature wound of the Iraq war"
Armor protects the body sure... but not the gooey bits inside. It's a similar reason to why they always try to convince you to go to the ER when you have an accident and thanks to the protection of your seatbelt/airbag/etc "feel fine"
Ad to the rigid armor gets hit, not the wearer bit... the wearer gets hit by the armor unless hat armor is capable of completely absorbing the entire blow and transferring the kinetic energy into something else (like a springy support structure)... but since armor you can't move is called a fortress rather than armor... lets stick with armor you can move around the world in without an external support structure like gets used in d&d

Armor protects the gooey bits inside as well. Both by deflecting and absorbing impacts. Just because there are limits doesn't mean this isn't so. Sure, they can't absorb the whole blow for many kinds of impacts, but that doesn't mean they don't absorb some of it. Those Iraq War vets? If they had helmets that didn't absorb some of the impact, they might well be dead from traumatic brain injury.

You seem to be using the fallacious reasoning that if the protection isn't perfect, then it isn't protection at all. This is decidedly not the case. The protection only becomes worthless when even with it an attack would be fatal or an attack is used that completely bypasses it (like a sonic attack against someone only protected from ballistic impacts).

[Starbuck_II]

Cute... but you fail and miss the important bit about those gooey bits we all have.. you fail (http://en.wikipedia.org/wiki/Dementia_pugilistica), and ultrafail (http://www.usatoday.com/news/nation/2005-03-03-brain-trauma-lede_x.htm) with actual armor this time...
"A growing number of U.S. troops whose body armor helped them survive bomb and rocket attacks are suffering brain damage as a result of the blasts. It's a type of injury some military doctors say has become the signature wound of the Iraq war"
Armor protects the body sure... but not the gooey bits inside. It's a similar reason to why they always try to convince you to go to the ER when you have an accident and thanks to the protection of your seatbelt/airbag/etc "feel fine"
Ad to the rigid armor gets hit, not the wearer bit... the wearer gets hit by the armor unless hat armor is capable of completely absorbing the entire blow and transferring the kinetic energy into something else (like a springy support structure)... but since armor you can't move is called a fortress rather than armor... lets stick with armor you can move around the world in without an external support structure like gets used in d&d

Cute, but while mentally damaged, body armor makes you survive deadly wounds.

So Truck doesn't kill you, just damages you. Which is what everyone is saying. Your links cvonfirm that. You need to show links that show your evidence not back up other people's. You don't argue internet very well :smallwink:

[Retech]

Also keep in mind that the brain is floating suspended in various layers of goo and tissue, so it can often be treated as a separate entity.

It's like an unbuckled passenger in a fast moving car. When it stops or when it starts quickly, they go flying.

[herrhauptmann]

Saw this happen at an SCA event once, even if it was by accident. Funny as hell to see a guy in full plate get hit, only to brush himself off and saunder on his merry way while the owner of the vehicle had to call a tow truck.

Which event was this? One of the wars?
One of our locals had a tree get launched at him from a tornado that ripped through a campsite one evening. He survived because he was still in his armor.
Though it did take about half an hour with saws for them to get the tree to a manageable size and lift it off of him. And the whiplash from getting hit by a tree was enough to mess up his neck and back years down the road.

I'm wondering, how many of those soldiers mentioned are suffering from brain damage just due to their brains getting rattled around inside their skulls. You know, shaken baby effect. All the armor and padding in the world won't help you if getting launched by an IED is rattling your brain like that.

[Tetrasodium]

Which event was this? One of the wars?
One of our locals had a tree get launched at him from a tornado that ripped through a campsite one evening. He survived because he was still in his armor.
Though it did take about half an hour with saws for them to get the tree to a manageable size and lift it off of him. And the whiplash from getting hit by a tree was enough to mess up his neck and back years down the road.

I'm wondering, how many of those soldiers mentioned are suffering from brain damage just due to their brains getting rattled around inside their skulls. You know, shaken baby effect. All the armor and padding in the world won't help you if getting launched by an IED is rattling your brain like that.

good example.... you probably won't find many stories about "short term" & unique things like that, but the guy's armor functioned exactly like the alternate rules are structured... he was hit by something bigger (the tree) and got messed up bad, but the armor's DR reduced that to merely bad instead of pulp

After my car accident (druing & pseudo-Tboned but he hit engine indstead of emprt passenger seat area) where I got spun around Hard, never hit an airbag(seatbelt held me)... I walked away fine, but the next day I culdn't even sit up and it was a good month or two untill the massive bruising was reduced enough for me to sit up

[Drachasor]

Also keep in mind that the brain is floating suspended in various layers of goo and tissue, so it can often be treated as a separate entity.

It's like an unbuckled passenger in a fast moving car. When it stops or when it starts quickly, they go flying.

The "goo" is actually a design feature. It helps absorb any impacts so that there is less damage (the brain responds to impacts slower). Be assured brain damage would be far, far, far more common without it.

[nihil8r]

i hate to derail the "does wearing armor protect you from being run over by a cement truck" conversation we have going :smallsmile:, but let's get back to the stupidity of these optional rules, which are meant to model melee combat and not vehicular homicide. i'm no mythbuster, but i'm pretty sure we need to be comparing the force of a human swinging a sword against the force of a large-size human swinging a sword, not against the force of a submarine dropped from orbit. although ... a submarine dropped form orbit is the perfect thing to use against my 1st level characters next game session ... :smallamused::smallamused::smallamused:

[Tetrasodium]

i hate to derail the "does wearing armor protect you from being run over by a cement truck" conversation we have going :smallsmile:, but let's get back to the stupidity of these optional rules, which are meant to model melee combat and not vehicular homicide. i'm no mythbuster, but i'm pretty sure we need to be comparing the force of a human swinging a sword against the force of a large-size human swinging a sword, not against the force of a submarine dropped from orbit. although ... a submarine dropped form orbit is the perfect thing to use against my 1st level characters next game session ... :smallamused::smallamused::smallamused:

A lot of what's been said is accurate in game situations, if say... a bull charges you... armor or not, you are likely to be hurt even if the armor lessens thedamage

[Infernalbargain]

Here's what I hate about the armor as DR: it makes AC worthless.

[Tetrasodium]

Here's what I hate about the armor as DR: it makes AC worthless.

How do you figure? the system in UC isn't simply ac converting to DR. It has a defence class of DC=10+shield mod+dex mod+deflection+dodge bonus+etc Bonus that acts exactly like AC. Then it takes regular/natural armor, and makes them DR/Armor (sorta like DR/- but better) with an extra +1 bonus every 5 levels/HD. DR/Armor stacks with other types of DR... so a target with 15 AC who gets stoneskin cast on them for DR10/adamantine has DR 15/Armor,Adamantine/25 making even small amounts of DR useful when combined with this

when an attacker makes a critical threat, the confirmation is handled differently, specifically the defender makes a crit defense check of Critical defense check bonus = creature’s DR + Dexterity modifier + shield bonus to Defense + deflection bonus against a DC of Critical defense DC = critical hit roll + 1/2 attacker’s base attack bonus + 1 for each critical feat + 1 for each size category larger attacker is than target

The sightly strange part is how different types of armor have different was of defeating the DR, but now that I look over that again I don't think it's so strange. They still sttack though
-Nonmagic armor (i.e. masterwork & worse) is DR/Magic or large attackers... Not too bad though, If your wearing that kind of armor, even a +1 weapon or things with magic natural attacks is still pretty scary for a few more levels.
-Magical Armor (I.E. +1 or better). DR/Adamantine or huge attackers. Huge attackers are pretty scary and adamantine is supposed to be this uber metal that ignores hardness... but that property is rarely ever relevant.
-Adamantine Armor gives you DR/- Suddenly that DR2/Adamantine on adamantine armor looks a whole lot more appealing when you are going to add the armor's total AC to it and just have two less in tho off chance that an someone uses an adamantine weapon on you. Gargantuan ttackers bypass that DR/-... but hell... gargantuan things should probably be freaking scary anyways.

[Infernalbargain]

How do you figure? the system in UC isn't simply ac converting to DR. It has a defence class of DC=10+shield mod+dex mod+deflection+dodge bonus+etc Bonus that acts exactly like AC.

That is touch + shield. Yeah, that's not going to be very high against regular attacks. It's already near impossible for AC to keep up with attack bonus, and now they're getting rid of one of the biggest components of it.

[Tetrasodium]

That is touch + shield. Yeah, that's not going to be very high against regular attacks. It's already near impossible for AC to keep up with attack bonus, and now they're getting rid of one of the biggest components of it.

You get huge amounts of DR in its place though

[Stone Heart]

I do want to point out, its not large creatures, but Huge creatures that can bypass a medium creatures DR in this way. Also Adamantine armor moves it up to gargantuan.

[Greenish]

You get huge amounts of DR in its place thoughHow does that address his complaint (that it makes AC worthless)?

[nihil8r]

A lot of what's been said is accurate in game situations, if say... a bull charges you... armor or not, you are likely to be hurt even if the armor lessens thedamage

yes, i agree that a bull charging you is bad. but a bull biting you isn't so bad. and having both of those attacks automatically ignoring armor because they come from a large creature is sparta-quality madness. if the bull needs extra damage or armor penetration when it's charging, fine. but simply getting de facto armor bypass based on volume alone? that's madness! :smalltongue:

[Tetrasodium]

How does that address his complaint (that it makes AC worthless)?

the system has been explained more than once in pretty good detail, with reasons why it does good things actually explained. I can't see how explaining it again because somebody didn't feel like reading one of those posts (http://www.giantitp.com/forums/showpost.php?p=11691355&postcount=43) is going to make them read it again. saying you get lots of R was a simple attempt to get past the TL;DR problem here. AC is still used, just different components of it go towards either DR or DC. Because its already explained in detail what benefits different types of AC give, if you still feel AC isn't getting enough ... there needs to be an explication of what types of AC aren't getting enough and why it's felt that it's made "worthless".

In short... your question has already been answered in the thread, and if you still feel that way after putting aside the TL;DR, there will need to be more detail given about your reasons for feeling that way.

[Drachasor]

You get huge amounts of DR in its place though

Which goes away under stupid conditions.

Example: Mature Adult Red Dragon barely hits someone with no armor a wing buffet, and it deals 6 damage. Hits another person with the same attack who is in full plate, has DR...and the DR does nothing to stop such a piddling attack? It makes no sense. The armor WOULD cushion the blow.

And there are plenty of other examples of huge creatures with piddling attacks. It's worse if large attacks can overcome it.

And like the other poster said, if you tremendously reduce AC in D&D, then AC does become worthless, because it is a tough struggle keeping AC high enough to be relevant for a lot of classes at higher levels.

Edit: I am using low damage attacks of big creatures just as a thought exercise.

[Knaight]

A lot of what's been said is accurate in game situations, if say... a bull charges you... armor or not, you are likely to be hurt even if the armor lessens thedamage

Or if some massive dragon smacks you with a tail. The upper size monsters would reasonably hit like vehicles, and armor would be about as useful as with vehicles. Which, in the case of stiff plate, might actually be pretty significant, judging by what people on the thread have seen.

[Tetrasodium]

Which goes away under stupid conditions.

Example: Mature Adult Red Dragon barely hits someone with no armor a wing buffet, and it deals 6 damage. Hits another person with the same attack who is in full plate, has DR...and the DR does nothing to stop such a piddling attack? It makes no sense. The armor WOULD cushion the blow.

And there are plenty of other examples of huge creatures with piddling attacks. It's worse if large attacks can overcome it.

And like the other poster said, if you tremendously reduce AC in D&D, then AC does become worthless, because it is a tough struggle keeping AC high enough to be relevant for a lot of classes at higher levels.

Edit: I am using low damage attacks of big creatures just as a thought exercise.

So change it from simply size to bypass to size difference to bypass. As to the wing buffet attack... it has piddling damage because it includes other effects. You struggle to keep it high enough in core because things happen(armor stops getting better/caps out/etc) when the system starts to break down to help stave off the point where anything full BaB classes have trouble hitting is impossible for partial BaB classes or full is autohit if partial can hit it. Under the modified optional rule, you could continue to adace armor (base, enhancements, dex caps, etc) without breaking the game in two.

[Drachasor]

So change it from simply size to bypass to size difference to bypass. As to the wing buffet attack... it has piddling damage because it includes other effects. You struggle to keep it high enough in core because things happen(armor stops getting better/caps out/etc) when the system starts to break down to help stave off the point where anything full BaB classes have trouble hitting is impossible for partial BaB classes or full is autohit if partial can hit it. Under the modified optional rule, you could continue to adace armor (base, enhancements, dex caps, etc) without breaking the game in two.

Here's an idea, don't have it bypassed based on size and the DR component doesn't break down at all. That's because the size-based component IS stupid and ill-conceived.

The whole point of this thread is that the DR optional rule in Ultimate Combat is dumb. If you are proposing a optional rules to fix it (and you are, if only in vague terms), then the case has been made.

[Fouredged Sword]

As a general rule, the attacks people imagine bypassing DR are infact the attacks that DEAL LOTS OF DAMAGE.

Just becuse something is big doesn't mean it hits hard. Platemail will protect a person from large impacts. Try running into a wall, then put on football(american) pads and run into that same wall. Did your armor protect you? Does it matter how big te wall was? The real world physics is the same as if the wall was comeing at you. All that matters is the impact and it's surface area (meaning that for a given impact force and time, smaller objects hurt armor more) Armor works to effectivly spread the impact over a larger surface area.

The rules fail to fit into my image of reality and thus distract from my suspension of disbelief.

Here is the thing. Just let those attacks deal lots of damage rather than give an arbetrary advantage to anyone who handle animals a pack of dire elephants.

[Knaight]

Just becuse something is big doesn't mean it hits hard. Platemail will protect a person from large impacts. Try running into a wall, then put on football(american) pads and run into that same wall. Did your armor protect you? Does it matter how big te wall was? The real world physics is the same as if the wall was comeing at you. All that matters is the impact and it's surface area (meaning that for a given impact force and time, smaller objects hurt armor more) Armor works to effectivly spread the impact over a larger surface area.

The physics are not the same. For one, after the collision one stops moving forward on their energy. However, if the wall was coming at someone, and it was what was moving, it would probably keep moving after the initial hit, which changes things. Moreover, that is one incredibly sluggish wall. A human punch or kick is moving much faster than even human sprinting speed, if one looks at the object connecting. Something larger than a human presumably hits even faster -consider the swung dragon tail, which cuts a wide arc very quickly if it has any chance to hit someone.

Moreover, the whole big-lots of damage paradigm is screwed anyways, unless you take hit points only to represent physical injury. The mechanics support that, but it isn't good for genre emulation if one wants to maintain suspension of disbelief without going into superheroes.

However, getting back to size and armor, armor as DR in the big damage paradigm takes care of that. It is only with armor as AC where scaling the armor down with size makes any sense at all, unless damage doesn't scale with size.

[NecroRick]

It might be there because they decided that the penalty for being larger than the opponent was too much and didn't make sense either.

Anything to make the munchkins come up with a new way of beating the system other than being a pixie is a refreshing change.

[Fouredged Sword]

Velocity is a vector. It maters not if you are having your speed slowed to match the wall or increased to match the flying wall. The change in velocity is the same. The end result is you traveling at the same speed as the wall. After that the wall is simply pushing you, and failing something to drag you on that could damage you it would be no more damageing than siting in a car is despite the fact that the car is moveing.

The issue with speed and focus of the blow is just a mater of scaleing. You move from mild damage -> no damage with armor to Severe damage - > heavy damage with armor. Even then, plate would protect you significantly even from a 60-70 mile an hour car crash. Would it save your life, maybe, but your chances would improve significatly over a non armored person, and even if you dies your body would be in a much better shape to be buried becuse it sustained much less damage before your brain turned to jelly.

[Knaight]

Velocity is a vector. It maters not if you are having your speed slowed to match the wall or increased to match the flying wall. The change in velocity is the same. The end result is you traveling at the same speed as the wall. After that the wall is simply pushing you, and failing something to drag you on that could damage you it would be no more damageing than siting in a car is despite the fact that the car is moveing.


So you assume a constant speed then. This isn't a safe assumption by any means, particularly as what we are looking at is sudden deceleration, and the sudden deceleration of something that hits something that is itself accelerating in the opposite direction is drastically different than sudden deceleration following a collision at a constant velocity. Most vehicular collisions fit in the first category, not the second, as do strikes done in a combat situation.

[Hiro Protagonest]

The reason it's stupid that the DR goes away when facing someone larger is because that's already been factored in, by a size increase to strength and a higher weapon damage.

[Fouredged Sword]

One target being stationary is the assumption of a car->pedestrian impact as well as the assumption of a weapon -> person impact, as you are unlikely to be throwing yourself into the strike, and there are critical hit rules to show what happens when such an even happens.

Ether way armor blunts an impact by defuseing the effect of the blow, absorbs energy by deforming, and prevents secondary damage due to secondary impacts (such as being thrown by the car or falling over after being hit by a large creature)

Being hit by a collosal creature has more to do with being hit bay a car than being stabed.

[Tetrasodium]

So you assume a constant speed then. This isn't a safe assumption by any means, particularly as what we are looking at is sudden deceleration, and the sudden deceleration of something that hits something that is itself accelerating in the opposite direction is drastically different than sudden deceleration following a collision at a constant velocity. Most vehicular collisions fit in the first category, not the second, as do strikes done in a combat situation.

He's right.. a head on collision in a parking lot with two cars each going 25mph is the same as each going 50mph into brick wall cable of withstanding the impact without breaking down to allow the car to pass through with reduced momentum. When you swing a weapon in an arc, the outer bit is moving much faster than your hand... it's why the tip of a whip is able to break the sound barrier and crack

[Knaight]

He's right.. a head on collision in a parking lot with two cars each going 25mph is the same as each going 50mph into brick wall cable of withstanding the impact without breaking down to allow the car to pass through with reduced momentum. When you swing a weapon in an arc, the outer bit is moving much faster than your hand... it's why the tip of a whip is able to break the sound barrier and crack

A head on collision with two cars going 25 miles per hour is the same as one hitting a wall at 25 miles per hour. Though this is obviously an oversimplification that ignores the size of the front of the car.

That said, if one manages to run into a wall at the speed of a swung weapon or body part, one is probably worthy of nomination as superhuman.

[NecroRick]

The reason it's stupid that the DR goes away when facing someone larger is because that's already been factored in, by a size increase to strength and a higher weapon damage.

not so, those simply attempt to balance the advantages that smaller opponents get. My point was that perhaps peezoo felt that the balance wasn't right, and that for whatever reason, whether balance, cinematic concerns or merely subjective they felt this would improve the game.

I now return you to the playgrounds favourite game: pretending that subjectives are absolutes and that ambiguity is clarity.

[Ravens_cry]

I have not looked through it, but by the sound of it and the kind of grumbling we are getting, it might work better in a campaign where most opponents are humanoid all the way to 20, a very 'gritty' game, and mythical and fantastic creatures are almost as rare as in Reality, being unique and awesome.
Which would be pretty cool I think if done right and gone in with the right expectations.

[Drachasor]

A head on collision with two cars going 25 miles per hour is the same as one hitting a wall at 25 miles per hour. Though this is obviously an oversimplification that ignores the size of the front of the car.

This is not the case. An impact of two cars moving at 25mph, has an energy of m25^2+m25^2 = 2m625=1250m (in units of pounds*miles^2/hour^2), where m is the mass of a car (we're assuming cars of the same mass).

This is the same energy as a car (of mass m) hitting a wall moving at 50mph.

Well, the effect on the passengers is different here, since the wall is rigid and doesn't absorb the impact as much as another car. In this case the car acts like armor for the occupants. I think we can all agree it is better to hit a wall in a car moving at 50mph than without a car moving at 50mph. Armor helps, even if it doesn't stop all damage.


not so, those simply attempt to balance the advantages that smaller opponents get. My point was that perhaps peezoo felt that the balance wasn't right, and that for whatever reason, whether balance, cinematic concerns or merely subjective they felt this would improve the game.

I now return you to the playgrounds favourite game: pretending that subjectives are absolutes and that ambiguity is clarity.

Smaller opponents don't get much in the way of advantages. Now, small races are kind of nice for players, because the strength differences are tiny and balanced out a bit by the to-hit bonus, and on top of that you get a boost to your AC. Big enemies, on the other hand, have immense strength bonuses, AC coming from natural armor and whatever the creator feels like, and they also get reach. I've never noticed big NPCs suffering at all due to their size. Why exactly do you think they are doing badly? Oh, and they also benefit because fewer of them fit into area effect spells.

Making up a story about "balance concerns" when you don't even know of (or at least don't offer) any balance concerns seems a bit silly.

What it does do is increase the number of things a player has to remember. Hurt verisimilitude against small hits by big creatures, hurts non-casters by making AC worthless and the compensating DR worthless against many foes.

I guess we can agree they probably made up a reason to do it. That does nothing to make it a good idea for an optional rule though.

[Fouredged Sword]

The math fails becuse you assume that the two cars come to a stop regardless of their velocity. If two cars with equle mass collide, the initial impact will leave both cars moveing sideways at a particular velocity, reduceing the inital impact.

Hitting a grounded and stationary object causes signifiactly more damage that a non grounded stationary object.

Physics aside though, armor helps no mater what hits you, it just is a question of whether it is enough to really help.

Though with the rules as it, I don't know why anything over a particular size would wear armor at all, as thier standard attacks would all bypass it, and thus like sized threats would bypass it as well.

[Drachasor]

The math fails becuse you assume that the two cars come to a stop regardless of their velocity. If two cars with equle mass collide, the initial impact will leave both cars moveing sideways at a particular velocity, reduceing the inital impact.

The math works fine. Energy is neither created nor destroyed. Energy before the collision is the same as the energy during is the same as the energy after.


Hitting a grounded and stationary object causes signifiactly more damage that a non grounded stationary object.

Yes, but the impact doesn't have any more energy in it. This is because the stationary object (and very rigid) doesn't mitigate the impact in any way, unlike how a car gets deformed (e.g. the change in momentum is less sudden). I addressed this.

Note that if we had two moving objects that weren't cars, but were say, solid pieces of metal, there'd be no real difference at all between the two cases.

That said, a moving arm or the like isn't nearly as rigid as wall. Your body will absorb and lessen the effect of an impact by a weapon you wield.


Physics aside though, armor helps no mater what hits you, it just is a question of whether it is enough to really help.

Though with the rules as it, I don't know why anything over a particular size would wear armor at all, as thier standard attacks would all bypass it, and thus like sized threats would bypass it as well.

It's size relative to you, in order to make it more complicated. Obviously if you are attacking a huge creature, bypassing the armor is impossible -- whereas it should generally make more sense to be able to do it, since small holes in protection become massive ones to smaller creatures (assuming you have flight or some other means to reach it).

The optional rule fails on many levels.

[Ravens_cry]

They tested (http://en.wikipedia.org/wiki/MythBusters_%282010_season%29#Episode_143_.E2.80.9 3_Mythssion_Control)this on Mythbusters and compared damage. (spoilers)

[Stone Heart]

How does that address his complaint (that it makes AC worthless)?

Where in my post did I say I was addressing that complaint? I was just pointing out that people kept saying large creatures would bypass it, but I wanted to clarify that its not the case.

[Fouredged Sword]

Energy isn't destroyed, but it is transfered outside the system if the impact. Otherwise it would be imposible for two objects to stick together. The starting energy is always higher than the ending energy.

In reality all impacts fall somewhere between completely inelastic and perfectly elastic. Some energy is always lost and some velocity is normaly maintained until friction stops the mass or masses after the impact is over.

[Drachasor]

They tested (http://en.wikipedia.org/wiki/MythBusters_%282010_season%29#Episode_143_.E2.80.9 3_Mythssion_Control)this on Mythbusters and compared damage. (spoilers)

Yeah, and that's egregiously wrong thinking. The force of the impact with a single car gets divided between the wall and the single car as well.

Sometimes Mythbusters has horrible science.

The apparent damage looking the same is more likely because cars get crushed on impact. That makes the impact less intense, because it essentially slows down the cars during the impact. Like they say, it isn't the fall that kills you, but the sudden stop at the end. The sudden stop with two cars crashing is less sudden than one, because crushing absorbs impact damage. This is a design feature of cars.

To help clarify this, consider an container for an egg designed to keep the egg intact after a 40 foot drop. It doesn't use parachutes. Now, when you drop it from 40 feet, you expect the container to be damaged -- afterall it gets dented absorbing the impact so the egg doesn't have to.

Now, create a long, wide tube, 40-some feet high. At the bottom, place one such egg container holding an egg. 40 feet above that, drop another. The damage to each container will be less, because the force is the same, but each slows down the effect of the impact. That "sudden stop" is even less sudden now.

So yeah, you'd EXPECT the damage to the cars to be less even if the energy of the impact is the same.

[Infernalbargain]

A head on collision with two cars going 25 miles per hour is the same as one hitting a wall at 25 miles per hour. Though this is obviously an oversimplification that ignores the size of the front of the car.

No, you are factually wrong. This might be helpful for you to understand the physics. (http://www.google.com/products/catalog?q=giancoli+physics&hl=en&safe=off&rlz=1C1CHFX_enUS400US400&prmd=ivnsb&resnum=4&bav=on.2,or.r_gc.r_pw.&biw=1440&bih=815&um=1&ie=UTF-8&tbm=shop&cid=2331040955407452349&sa=X&ei=tr9STufhOsqJsgLhzaXZDA&ved=0CG0Q8wIwAQ)

Remember the 1st postulate of physics: the laws of physics are the same in all inertial reference frames. So if in the stationary reference frame (v=0), one car heading to the left at 25mph and another heading to the right at 25 mph (they're heading towards each other, not away), the physics must be identical to the reference frame that is moving at 25mph to the left. In that reference frame, the first car is travelling at 50mph and the second car is travelling at 0 mph.

[Knaight]

Remember the 1st postulate of physics: the laws of physics are the same in all inertial reference frames. So if in the stationary reference frame (v=0), one car heading to the left at 25mph and another heading to the right at 25 mph (they're heading towards each other, not away), the physics must be identical to the reference frame that is moving at 25mph to the left. In that reference frame, the first car is travelling at 50mph and the second car is travelling at 0 mph.

A car crashing into a stationary car and a car crashing into a wall are two very different things. Much as a car that hits a mosquito at 25 miles an hour that is traveling towards it at 25 miles an hour is different than a car that hits a car at 25 miles an hour traveling towards it at 25 miles an hour.

As stated above, Mythbusters tested this, and the actual data bears out that crashing two cars into each other at 25 miles an hour is approximately equivalent to crashing one into a wall at 25 miles an hour. Its counter intuitive at best, as that is functionally the same as one car crashing into a stationary car at 50 miles per hour as per the reference frame from either car, but its what the data indicate. Its not particularly surprising however, as what matters here is deceleration, which varies depending on what part of the car. The front of the car that hits the wall at 50 miles an hour decelerates far faster than the front of the car that hits the other car at 50 miles an hour, as the wall isn't itself getting crushed and effectively pushed further away from the front of the crashing car, and the other car is.

In short, in a Newtonian model, two objects of velocities X and -X that crash (speed X for both, opposite directions) are the same as an object with velocity 2X that crashes into something with velocity 0. So, in a simple Newtonian model, you are completely right. However, this doesn't work well when comparing a crash where both entities deform significantly, and where only one deforms significantly, simply because in the one where both deform the acceleration is lower, because the crash effectively happens over a longer period due to the introduction of what basically works as decelerating over a longer distance in the same period of time.

[Infernalbargain]

A car crashing into a stationary car and a car crashing into a wall are two very different things. Much as a car that hits a mosquito at 25 miles an hour that is traveling towards it at 25 miles an hour is different than a car that hits a car at 25 miles an hour traveling towards it at 25 miles an hour.

As stated above, Mythbusters tested this, and the actual data bears out that crashing two cars into each other at 25 miles an hour is approximately equivalent to crashing one into a wall at 25 miles an hour. Its counter intuitive at best, as that is functionally the same as one car crashing into a stationary car at 50 miles per hour as per the reference frame from either car, but its what the data indicate. Its not particularly surprising however, as what matters here is deceleration, which varies depending on what part of the car. The front of the car that hits the wall at 50 miles an hour decelerates far faster than the front of the car that hits the other car at 50 miles an hour, as the wall isn't itself getting crushed and effectively pushed further away from the front of the crashing car, and the other car is.

In short, in a Newtonian model, two objects of velocities X and -X that crash (speed X for both, opposite directions) are the same as an object with velocity 2X that crashes into something with velocity 0. So, in a simple Newtonian model, you are completely right. However, this doesn't work well when comparing a crash where both entities deform significantly, and where only one deforms significantly, simply because in the one where both deform the acceleration is lower, because the crash effectively happens over a longer period due to the introduction of what basically works as decelerating over a longer distance in the same period of time.

Yes the velocity isn't everything because it's conservation of momentum that gets applied. However, you can't claim that two cars going at 25 is equivalent to car going a wall at 25. Throwing in things like deformation makes the calculation immensely more complicated. It may be that he threw out a number for which it held, but if so, it isn't gonna hold for 30mph or any other speed.

[Drachasor]

The thing to remember here is that getting clawed by a dragon is NOT like crashing into a wall. The wall is far more immobile. The dragon's body will absorb and lessen part of the impact, because the impact is bad for the dragon too. Same with a giant, etc, etc.

[Doug Lampert]

This is not the case. An impact of two cars moving at 25mph, has an energy of m25^2+m25^2 = 2m625=1250m (in units of pounds*miles^2/hour^2), where m is the mass of a car (we're assuming cars of the same mass).

It burns. Argh!

Alright,
(1) it's 1/2 m v^2, so 625 units.
(2) the single car at 50 mph does 1/2 m50^2 which is 1/2 2500m which is 1250 units, twice the energy.
(3) In the case of two cars both cars crumple absorbing energy, hence each absorbs half the total energy or 312.5 units. Exactly the energy one car brings to the collision by no particular coincedence.
(4) The wall does not crumple, the single car absorbs all the energy or all 1250 units.
(5) Mythbusters had Jamie make the exact same mistake you did. They then tested it by colliding multiple cars with each other and a wall, their conclusion matched the physics, that dead stopping a car from 25 mph via impact is the same whether you do it by hitting a wall or another car. Either way it absorbs the same energy.

You are wrong. Badly.

The math YOU POSTED is wrong. Twice over, once when you can't use 1/2 in your energy equation, and the second time when you claim that 50^2 is 1250 when two seconds with a calculator would tell you this is wrong. Or two seconds of thought about the fact that 1^2+1^2 is not equal to 2^2. Exponentiation is not associative.

Please stop arguing physics.

DougL

[Drachasor]

It burns. Argh!

Alright,
(1) it's 1/2 m v^2, so 625 units.
(2) the single car at 50 mph does 1/2 m50^2 which is 1/2 2500m which is 1250 units, twice the energy.
(3) In the case of two cars both cars crumple absorbing energy, hence each absorbs half the total energy or 312.5 units. Exactly the energy one car brings to the collision by no particular coincedence.
(4) The wall does not crumple, the single car absorbs all the energy or all 1250 units.
(5) Mythbusters had Jamie make the exact same mistake you did. They then tested it by colliding multiple cars with each other and a wall, their conclusion matched the physics, that dead stopping a car from 25 mph via impact is the same whether you do it by hitting a wall or another car. Either way it absorbs the same energy.

You are wrong. Badly.

The math YOU POSTED is wrong. Twice over, once when you can't use 1/2 in your energy equation, and the second time when you claim that 50^2 is 1250 when two seconds with a calculator would tell you this is wrong. Or two seconds of thought about the fact that 1^2+1^2 is not equal to 2^2. Exponentiation is not associative.

Please stop arguing physics.

DougL

So I forgot a 1/2 and then didn't properly calculate the speed of an equally energetic car (that's 35.35mph, btw). That's two minor math mistakes. Big deal.

The fact is the wall DOES absorb half the energy. Half the force of the impact IS applied to the wall. That's a far, far more basic mistake you are making, and a far more critical mistake than a simple math error. At each instant, a fraction of the force of the impact is applied to both the wall AND the car. The car reacts different than the wall because of what it is made of, but the wall still absorbs the same amount of force.

For the love of physics, you are acting like the force applied to the wall magically bounces back and hits the car and not the wall, violating Newton's Third Law. That's extremely wrong at a fundamental level.

Just because the wall is more rigid than the car does not mean it somehow doesn't get the same force applied to it in the impact. Two cars running at each other at 25mph is NOT the same as one hitting a wall at 25mph, even if the cars look equally smashed at the end of that.

Keep correcting math, but you need to reconsider the physics here.