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Old Aug 13th, 2014, 02:37 PM
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Questions about gravity

Hey all. So I'm studying for an astronomy final at the moment and a thought occurred to me that I thought I'd share.

Normally we assume that our intrepid adventurers stick to a relatively Earth-like planet with standard gravity, atmosphere, etc. When we transport between planes, things generally don't change. Is this reasonable? I find it difficult to believe that a plane with significantly different material make-up would have comparable gravitational properties. And let's say gravity does change: how would you handle things like move speed, encumbrance, and projectiles? Would the magical nature of the world simply counterbalance such changes?

Food for thought.
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Old Aug 13th, 2014, 05:04 PM
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Don't have the different planes have different gravity because "they have different material make-up." If you think an adventure in low or high gravity would be fun and fit the tone and themes of your game, then do it. In other words, don't do it out of some loyalty to "realism." Do it because it would be fun.

And I would handle low gravity using the underwater combat rules.

Last edited by RedRab; Aug 13th, 2014 at 05:04 PM.
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Old Aug 17th, 2014, 06:58 AM
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Or you could give players a magical item like boots or something that gives them the ability to move about in low/hi gravity as if it were normal, and then those native to the land could just be used to the environment and so move about as naturally as normal gravity
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Old Aug 17th, 2014, 08:12 AM
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So my question is how do you strike the balance between realism and player experience? I'm an engineering student, so science and physics are always something I consider (which is a big part of why I find the commoner railgun so fascinating). At what point does this impede the game's progression? Does this enhance creative opportunity, or hinder it?
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Old Aug 17th, 2014, 02:37 PM
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You are asking a question that is purely a matter of taste.

For my tastes, "realism" is all about genre expectations. If I am watching Gravity, and an astronaut goes outside the space station with a breathing mask over her mouth and eyes and no other protection, then it's stupid. I'm watching "hard science" fiction. It's supposed to at least give the illusion of realism. But if I am watching Guardians of the Galaxy or The Empire Strikes Back and people go into outer space with just a mask over their mouths, I'm totally fine with it, because . . . at no point do I expect to see anything the least bit realistic in those movies.

Same with RPGS. When I play a game with elves and dwarves and vancian magic and talking bears and spells called "Otto’s Irresistible Dance" and magic items named "Sword of Yodeling" . . . I don't expect much in the way of realism.

Your mileage may vary.
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Old Aug 20th, 2014, 11:53 AM
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Well-put, RedRab! That's just the way I take it too. It's why I was able to accept Bill Pullman in the role of President of the United States in the movie Independence Day.
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Old Sep 8th, 2014, 02:55 PM
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I'm famous for once sitting back, puzzled, in the middle of a session and telling my players to "give me a moment while I ponder the properties of anti-light traveling through extra dimensional space."

It is not necessary for these sorts of physics to be realistic, but it is important that they make sense in the context of the world and in a way the players can understand. Gravity can be stronger or weaker for whatever reason you choose, but you should indeed choose a reason.

"Gravity is the same everywhere because all of the planes overlap one another and actually exist in the same space"

or "As you move up through the planes gravity weakens as you travel farther from the source, this is why higher dimensional being often fly about and travel via non-pedal movement"

or "Gravity is a divine construct; its sole purpose is to anchor evil souls to the ground, hence higher gravity in the 9 hells, medium gravity in material plane, and lesser or no gravity in the heavens"

You can have fun with it, or you can hit up wolfram alpha and calculate the gravity of a particular planet made of a particular material. Either way works, as long as your players are made to see the reasoning an consistency behind it.

Last edited by Dracc; Sep 8th, 2014 at 03:51 PM.
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Old Sep 8th, 2014, 02:58 PM
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Good points all around. I love the freedom that tabletop games provide, and I guess I was just trying to give the ruleset some framing.
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Old Feb 15th, 2015, 07:00 PM
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I belive DragonStar had rules about high and low gravity. It certainly had races from high and low gravity worlds.
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Old Feb 16th, 2015, 12:56 AM
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Quote:
Hey all. So I'm studying for an astronomy final at the moment and a thought occurred to me that I thought I'd share.
Firstly, I'd like to say, good luck.

Quote:
Normally we assume that our intrepid adventurers stick to a relatively Earth-like planet with standard gravity, atmosphere, etc. When we transport between planes, things generally don't change. Is this reasonable? I find it difficult to believe that a plane with significantly different material make-up would have comparable gravitational properties.
I've actually ran campaigns where my players have traversed through alternate planes of existence or travelled and landed on extraterrestrial planets. Being very scientific minded, I tend to interpolate ideas such as extra-gravity and even the very gases in the air that my players might breathe in.

On the record, however, the "differences" in physical compositions between planes doesn't factor into their respective gravity at all, unless we're specifically speaking of their collective masses. I.e. a heavier composite of materials is bound to exert a greater gravitational attraction regardless of the plane it inhabits.

But, what I've done is use dimensions (physical; diameter, volume, etc) to determine the "base" gravity of the new planet or plane, and allow the base numbers of my players reflect their new environment. If they weight 100 lbs on "earth" then they would weigh twice that much on a 2x gravity-mass planet.

Quote:
And let's say gravity does change: how would you handle things like move speed, encumbrance, and projectiles? Would the magical nature of the world simply counterbalance such changes?
You would use the "extra" weight from the gravity to alter their "loads" as if it were in fact just extra weight. A fighter with 20 strength and only 40 lbs of equipment isn't going to be greatly hampered by an increase of 2x gravity-mass, whereas the same fighter on a 5x gravity-mass might be at a medium or even heavy load. And their movement should be reflective of that. (And might just make more players appreciate Dwarves.)

Everything is effected by the additional gravity. Even how effectively one can use a weapon. I have generally given an effective penalty on attack rolls equal to the gravity increase, minus 1. I.e. (Penalty to attack rolls = n-1, where n = the total increase in gravity.) You can choose to give 1/2 the penalty as a bonus to damage to reflect the additional "weight" of the strike. It's made for some fun combats in my games.

Outside of that, I've just removed the "furthest" range increment for ranged weapons, for each increase beyond the "base" gravity. In 3.5e you could have 10 increments for projectiles, and only 5 for thrown. So in addition to the attack penalties, you would also be limited to how "far" you could shoot/throw your weapon. Always seemed to work for me whenever it came up.
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Old Feb 16th, 2015, 01:38 AM
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Quote:
Originally Posted by Eros View Post
Firstly, I'd like to say, good luck.
On the record, however, the "differences" in physical compositions between planes doesn't factor into their respective gravity at all, unless we're specifically speaking of their collective masses. I.e. a heavier composite of materials is bound to exert a greater gravitational attraction regardless of the plane it inhabits.
That is exactly what I was referring to. Newton's law of universal gravitation states that the gravitational pull of a body by the following:

F = GmM/r^2

Where G is the universal gravitational constant, m is the mass of the smaller body, M is the mass of the larger body, and r is the distance between them. In normal calculations, M is the mass of the planet while m is the mass of a creature standing on its surface. r then becomes the average radius of the planet, as we assume the center of mass to be the center of the planet. Since the player is changing locations, G and m remain constant, but M and r can change. Is the plane they travel to is composed of much denser material, then M increases, and though this wouldn't have as great an effect as altering the planet's diameter, it's not negligible.

Also, I totally passed that class
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Old Feb 16th, 2015, 02:50 AM
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I'd like to point out that I solve this problem more and more by doing science fiction games rather than fantasy games.

Oh, wait, my mistake that doesn't solve the problem, it makes it infinitely worse. I was doing orbital mechanics a few weeks ago as DM prep to give myself a clearer understanding of a fictional planet-moon system.

Actually, last I checked, the Positive and Negative Energy planes in D&D-style planar settings have pretty wacky and non-standard gravity rules.
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Old Feb 16th, 2015, 06:22 AM
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The Helliconia Trilogy by Brian Aldiss is a fantasy was the best use of orbital mechanics I have read in fiction. The books deserved to be more popular than they were. The fan made clip does a great job explaining how Helliconia orbits around its two sun and has a great year of over 2500 years.
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Old Feb 19th, 2015, 04:06 AM
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I believe this is from some off shoot of 2nd Eddition AD&D but I could be wrong. Certain planes (Fire, Air, and other diaphanous elements) don't have a planet, or anything of sufficent mass to generate gravity perceptible to humanoids. You just sit there suspended in place, often taking damage from whatever element you're now surrounded by. To live and travel within these planes took a bit of skill, and to travel within them, you had to focus a fix a point somewhere around you firmly in your mind. That point became your source of gravity and you "fell" towards it at the standard rate. This became fun because if you hit anything, like a wandering elemental, you would often take an obscene ammount of falling damage and inflict quite a bit of impact damage in mind.

Just thought I'd throw that out there since I haven't heard of anyone using plane mechanics like that in awhile. Cheers.
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Old Mar 13th, 2015, 01:04 AM
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I know this is kind of an older post, but it is new to me so I am gonna go ahead and add my 2 cents worth Keep in mind I am writing this at 1am and had to be at work at 6am yesterday, so might ramble a bit.

First off I am glad you passed the class

Second, I think how you solve this is entirely up to you as the GM. As long as it is logical within the confines of the current campaign I would go along with it. Keep in mind though I am a complete newb

I have no extended education but I thought of a couple things you guys haven't talked about, so thought I would share. Feel free to correct me

I noticed you talked about some of the effects of having twice as much gravity and how it would effect movement. However, no one brought up the fact that your body it's self would weigh twice as much, and the muscles in your legs would not be used to it, thus I think you would add your weight to your encumbrance as well as twice as much weight as what you are carrying.

On the other side of the coin, half gravity has a lot of effects that might not be obvious. Take bow and arrows for instance:

Without enough resistance from a properly weighted arrow the string and arms will move to violently and quickly, damaging the bow and possibly causing catastrophic failure. Compound bows will be more effected than re-curve / longbows. On the plus side, half weight arrows would have more arc as well.

In double gravity, arrows would weigh twice as much. This would cause causing the arrows to fly "flatter" (reducing the amount of arc), and reducing the effective range. Heavier arrows would hit harder, but only approx. 9%.

In either case, the farther out you are shooting the less accurate your going to be (compared to normal 5 - 9 grain arrows), but a lighter arrow will miss by a much smaller amount (~ 4" vs ~ 13" at 30 yards).

Just more to think about.

I believe however, that if a caster is powerful enough to travel to another dimension they are probably powerful enough to find a way to negate, or at least lesson, the effects of the gravity there.

Last edited by Leachim; Mar 13th, 2015 at 01:05 AM.
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