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    Default Gravity in D&D [PEACH]

    There's two factors to consider with gravity:
    - Gravitational Acceleration (GA)
    and
    - Air Resistance (AR)

    Steps to be taken in such an environment:
    - Multiply GA by object/creature weight to determine new weight of object/creature
    - Inverse Multiply GA by creature's jump modifier to determine new jump modifier
    - Inverse Multiply GA by distance required to fall to take on falling damage and incremental falling damage (10ft. on Earth).
    - Inverse Multiply AR by distance required to fall to take maximum damage (200ft. on Earth).

    D&D assumes Earth AR and GA. Earth's AR and GA are at 1.


    When the GM lists the stats for an environment, he lists a number beside AR and GA.

    So that's all there is to it.

    Example

    Planet X has GA 1/3 and AR 1/4. In order to take falling damage you must fall at least 30ft. You can take maximum falling damage at 800ft., which is 26d6. Objects weigh 1/3 of what they would on Earth. Jimmy has a +4 modifier to jump on Earth and +12 on Planet X.

    Also: At certain points (at GM discretion I suppose), falling speed is reduced. At certain levels of AR, air is much like liquid that you can make swim checks in it.
    ----

    Sound good? Now all we need is rules for vacuum.
    Last edited by imp_fireball; 2010-05-20 at 04:30 PM.

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    Default Re: Gravity in D&D [PEACH]


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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Ashtagon View Post
    Some of that doesn't really make sense.

    For falling into spike pits - Just add the spike damage and then apply a Str modifier, maybe +1 for every die of damage you took from regular falling damage? Also, reflex DC to avoid.

    I'm also pretty sure that terminal velocity is 200ft. in D&D.

    Swim check to dive seems reasonable. Also, water and soft surfaces does reduce falling damage, but not by much (in SRD I read this). Deeper water reduces falling damage by more too.

    I'm convinced that my system is simpler. :P
    Last edited by imp_fireball; 2010-05-20 at 04:34 PM.

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    Default Re: Gravity in D&D [PEACH]

    Question!

    Does gravity count as an effect affecting a character?
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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by The-Mage-King View Post
    Question!

    Does gravity count as an effect affecting a character?
    No Iron Heart Surge-ing away gravity.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Eurus View Post
    No Iron Heart Surge-ing away gravity.
    CURSE YOU! You sensed my evil plot!
    Last edited by The-Mage-King; 2010-05-20 at 06:14 PM.
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    Default Re: Gravity in D&D [PEACH]

    Without any gravity, you will be launched very quickly out of this planet, or into the nearest conveniently place wall, very much dead i'm afraid.

    EDIT: Important, this might just be if gravity for the WHOLE PLANET, was removed.
    Last edited by Kiren; 2010-05-20 at 07:23 PM.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by imp_fireball View Post
    Some of that doesn't really make sense.

    For falling into spike pits - Just add the spike damage and then apply a Str modifier, maybe +1 for every die of damage you took from regular falling damage? Also, reflex DC to avoid.
    I guess some modifier based on distance fallen is appropriate for spike pit damage. My main point on that line was to clarify that spikes are treated as a separate batch of damage from the fall itself.

    I'm also pretty sure that terminal velocity is 200ft. in D&D.
    By core rules yes, 200 feet is terminal velocity in D&D. But based on Earth norms for gravity and wind resistance, you normally hit terminal velocity after having fallen about 600 feet. So I changed it.

    Swim check to dive seems reasonable. Also, water and soft surfaces does reduce falling damage, but not by much (in SRD I read this). Deeper water reduces falling damage by more too.

    I'm convinced that my system is simpler. :P
    Fair enough. It just seemed worth putting the two side by side since they cover the same ground.
    Last edited by Ashtagon; 2010-05-21 at 12:50 AM.

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    Default Re: Gravity in D&D [PEACH]

    I proposed some rules for falling damage, ages ago, and aside from being proved wrong, there was lots of very good discussion about the dynamics of falling, acceleration due to gravity and air resistance.

    It's over here. Could be helpful.

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    Default Re: Gravity in D&D [PEACH]

    One thing that DnD really fails at in falling isn't acceleration or air resistance, its how blatantly they ignore the square to cube ratio. It really is true that the bigger they are, the harder they fall. A 40ft giant that fell twenty should break both his legs at the very least, while a halfling taking the same fall would probably be fine.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Apalala View Post
    One thing that DnD really fails at in falling isn't acceleration or air resistance, its how blatantly they ignore the square to cube ratio. It really is true that the bigger they are, the harder they fall. A 40ft giant that fell twenty should break both his legs at the very least, while a halfling taking the same fall would probably be fine.
    This is something which I chose to ignore in my rules for falling. The same physics that would cause a giant to break both legs from even a modest fall would also make it physically impossible for him to exist at all.

    At some point, physics has to make way for rule of cool.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Apalala View Post
    One thing that DnD really fails at in falling isn't acceleration or air resistance, its how blatantly they ignore the square to cube ratio. It really is true that the bigger they are, the harder they fall. A 40ft giant that fell twenty should break both his legs at the very least, while a halfling taking the same fall would probably be fine.
    Ahem - my house rules did that quite well (I think).

    I use an increasing size category damage die, so small creatures take d4s, medium take d6s, and so on.

    Let's not derail this thread any further, though!
    I like the GA / AR mechanic - it's quite neat. We tend to think in terms of "X on Planet Strange is Y% of Earth's X", so there shouldn't be any difficulty using this system (even when your house rules for falling are a bit different).

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    Quote Originally Posted by Ashtagon View Post
    This is something which I chose to ignore in my rules for falling. The same physics that would cause a giant to break both legs from even a modest fall would also make it physically impossible for him to exist at all.

    At some point, physics has to make way for rule of cool.
    Yeah, you say that, but then we're already having a discussion about how to make falling more realistic in the rules. I think there is a middle ground that can be found. The giant monster taking lots of damage on a fall is very cinematic too, I think. If you cause a colossal monster to topple over, the earth should shake and crumble, and the giant shouldn't go unscathed.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Ashtagon View Post
    This is something which I chose to ignore in my rules for falling. The same physics that would cause a giant to break both legs from even a modest fall would also make it physically impossible for him to exist at all.

    At some point, physics has to make way for rule of cool.
    Greater weight equals greater impact force with ground. But giants are generally tougher then halflings otherwise they can't stand up.

    Quote Originally Posted by Apalala View Post
    Yeah, you say that, but then we're already having a discussion about how to make falling more realistic in the rules. I think there is a middle ground that can be found. The giant monster taking lots of damage on a fall is very cinematic too, I think. If you cause a colossal monster to topple over, the earth should shake and crumble, and the giant shouldn't go unscathed.
    Maybe if the collossal monster is an elcor or an old man. Especially if they move very slowly for collossal creatures (anything less then 120ft. base speed is below collossal human, imo).
    Last edited by imp_fireball; 2010-05-23 at 01:55 AM.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by imp_fireball View Post
    Greater weight equals greater impact force with ground. But giants are generally tougher then halflings otherwise they can't stand up.
    It's more complex than that.

    First, let's take a spherical cow in a perfect vacuum...

    ok, bad metaphor. Let's take a human. He is 6 feet tall, weighs 150 lb and his feet cover an area of, let's say, 30 square inches. The ground pressure on his feet and (other supporting structures in his legs) is about 5 psi.

    Let's double his height to make a giant, but keep the same body proportions. He is now 12 feet tall, weighs (150x8) 1200 lb, and his feet cover (30x4) 120 square inches. Ground pressure is now 10 psi.

    Each time you increase the height while p[reserving body ratios, the pressure on supporting structures increases. Sooner of later there will come a point where the pressure on those supporting structures exceeds their ability to support that weight. For humans, that is surprisingly close to real-world heights. The world's tallest man suffered greatly from leg joint pain in the latter half of his life. An actual giant would likely die of arthritis.

    That's quite aside from issues such as circulatory systems. There is a large body of experts who believe dinosaurs had two hearts, for this specific reason. Insect-style respiratory systems are also impossible to scale up to anything much larger than, well, an insect.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Ashtagon View Post
    It's more complex than that.

    First, let's take a spherical cow in a perfect vacuum...

    ok, bad metaphor. Let's take a human. He is 6 feet tall, weighs 150 lb and his feet cover an area of, let's say, 30 square inches. The ground pressure on his feet and (other supporting structures in his legs) is about 5 psi.

    Let's double his height to make a giant, but keep the same body proportions. He is now 12 feet tall, weighs (150x8) 1200 lb, and his feet cover (30x4) 120 square inches. Ground pressure is now 10 psi.

    Each time you increase the height while p[reserving body ratios, the pressure on supporting structures increases. Sooner of later there will come a point where the pressure on those supporting structures exceeds their ability to support that weight. For humans, that is surprisingly close to real-world heights. The world's tallest man suffered greatly from leg joint pain in the latter half of his life. An actual giant would likely die of arthritis.
    The giant makes up for this with denser bones, different bones (or other factors like larger feet; an elephant has very wide feet). They'd probably weigh more then 1200lbs if they were 12 feet tall.

    Also, the world's largest man didn't weigh close to 1200lbs I don't think (maybe half that?).

    That's quite aside from issues such as circulatory systems. There is a large body of experts who believe dinosaurs had two hearts, for this specific reason. Insect-style respiratory systems are also impossible to scale up to anything much larger than, well, an insect.
    Possible, or the dinosaur has a much more powerful heart and arteries then proportion human. Or maybe their blood carries more oxygen? Or maybe they're diesel powered.
    ------

    Also, the view on the world does not need to be simplified, but the solutions should always be as elegant and as simple as possible.
    Last edited by imp_fireball; 2010-05-23 at 06:39 PM.

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    Compare the elephant to the rabbit. Rabbits are agile and leap with great ease. Elephants have so much pressure they can't jump. A giant humanoid would be even more unwieldy, having to balance on two feet. The cross-section of their legs would have to be even wider than that of an elephant, and such an abomination would probably splatter if it toppled over.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Apalala View Post
    Compare the elephant to the rabbit. Rabbits are agile and leap with great ease. Elephants have so much pressure they can't jump. A giant humanoid would be even more unwieldy, having to balance on two feet. The cross-section of their legs would have to be even wider than that of an elephant, and such an abomination would probably splatter if it toppled over.
    Elephants don't splatter when they topple over. You're also assuming a humanoid has human kneecaps. The giant would have tougher bones, tougher everything.

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    Default Re: Gravity in D&D [PEACH]

    Also, the world's largest man didn't weigh close to 1200lbs I don't think (maybe half that?).
    Robert Wadlow, 8 ft 11.1 in, 485 lb. Died age 22 from an infected ankle. The infection was caused by a leg brace that he needed to enable him to stand properly. Without such assistance he would have been confined to a wheelchair except for brief periods (a few minutes at a time).

    This pretty much matches my earlier statements about how a creature of basic human biology and body ratios much taller than a human would be effectively disabled.

    The current title holder is just under 10 inches shorter, and has no particular health issues, suggesting that the threshold where the human form can't properly support itself is somewhere between 8 ft 1 in and 8 ft 10 in.
    Last edited by Ashtagon; 2010-05-25 at 01:31 AM.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by imp_fireball View Post
    Elephants don't splatter when they topple over. You're also assuming a humanoid has human kneecaps. The giant would have tougher bones, tougher everything.
    Denser doesn't necessarily equal tougher. Solid bone wouldn't have the arch-like inner struts that real bone generally has.
    The biggest things to move around on land were the sauropod dinosaurs. Their limb bones were "solid" in that they didn't have big marrow-filled hollows in the centre, but the so-called "solid" bone was still spongy. The sauropods were typically maybe one order of magnitude bigger, volume-wise, than an elephant -- at least as far as limbs and torso went; their very long necks and tails were of course an additional consideration.
    There really is a limit to how much you can toughen a bone, or a muscle, or anything else. At some point you've got to admit magic of some sort.

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    Default Re: Gravity in D&D [PEACH]

    I've always imagined giants to have really thick powerful limbs - you'll need them to push all that mass around.
    The T-rex was around 13ft tall to the hips. It's estimated to weigh about 7.5 tons. Think of those legs, and imagine them more humanoid. You'll be in the right territory for verisimilitude.

    Of course, this doesn't have to hold true for inherently magical big creatures, like outsiders, or Titans.

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    Default Re: Gravity in D&D [PEACH]

    Quote Originally Posted by Ashtagon View Post
    Robert Wadlow, 8 ft 11.1 in, 485 lb. Died age 22 from an infected ankle. The infection was caused by a leg brace that he needed to enable him to stand properly. Without such assistance he would have been confined to a wheelchair except for brief periods (a few minutes at a time).

    This pretty much matches my earlier statements about how a creature of basic human biology and body ratios much taller than a human would be effectively disabled.

    The current title holder is just under 10 inches shorter, and has no particular health issues, suggesting that the threshold where the human form can't properly support itself is somewhere between 8 ft 1 in and 8 ft 10 in.
    A giant isn't the same as a human. Even if the human is as tall as the giant. Just because they look roughly human doesn't make them anywhere close to human. Same with humanoids. Orcs are realistically drastically different from humans except for the fact that they breath, eat, sleep and tire like humans and if you shoot one in the head or stab it in the heart, it'll die.

    But sure, if you want a fantasy setting, you can make them all 'ascetic non-human/human otherwise' and then declare 'rule of cool'.

    Solid bone wouldn't have the arch-like inner struts that real bone generally has.
    Okay, sure bone has to be hollow, but it can still be denser while remaining just as hollow and equally flexible. The downside is that it is generally heavier, hence why ogres are said to weigh upwards of 1000 pounds (in SRD).

    There really is a limit to how much you can toughen a bone, or a muscle, or anything else. At some point you've got to admit magic of some sort.
    I don't think so. Prior to extremophiles, people said that only magical creatures could exist under the earth or at the bottom of the sea or wherever. Just one example of science being nuts.

    Also, black holes. Oh, and dinosaurs in general. Tyrannosaurus is a biped - it doesn't use its tail to lift itself, just for balance.

    Even fast healing can be explained away with science (well pseudo-science; super skin, super organs, super metabolism; that way you wouldn't have an ultra-platelet scabby creature). Heck, soul transfer can be explained away with pseudo-science.

    Science can be used for fluff too - why are one iteration of goblins so scabby and warty? Their skin is fragile, but they have very high blood platelet and skin blistering capabilities. Their blisters and warts are also ultra tough. Hence, they look ugly. From time to time, they'll bleed for no reason but with no ill effect.

    Oh and also, mass distribution among bones, more internal non-limb joints (small, unmoving tough bones that absorb energy), etc. - other ways of not going the 'denser bones' route.

    Compare the elephant to the rabbit. Rabbits are agile and leap with great ease.
    What about 600lbs. (or whatever) tigers?
    Last edited by imp_fireball; 2010-05-25 at 05:22 PM.

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    Many catgirls died to bring us this information.
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    Ring of Evasion means never playing a monk with monk levels again. There is just no reason to dip that stuff. I know we're all about using every part of the buffalo here, but can we just admit that it's inedible?

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