The Laws of Physics

[Travinkel]

How do you handle this particuliar when you're building a world? According to the Newton's law of gravity (that an object of extreme mass will have lower mass objects orbiting it)?

Let's say a campaign world is 4 times as large as earth. We'll just assume the mass is 4 times larger as well, which means their gravitation would be 4 times the power of earth's. Now if a person would enter this world, through a dimension portal or something, he'd have a hard time there. He'd get back problems, amongst other things.

How do you handle these things? (any thoughts)

(It was more directed at campaign world builders)

 

[Jdvn1]

There's nothing to imply that a campaign world must be spherical, or that a universe is the same as our own universe. Everyone lives on "planes" which are flat surfaces, right?

I figure a world could be spherical, but it doesn't have to be. Physics aren't in the rules, and they don't always apply to D&D. Magic can be involved in the inner workings of the world. So, I try for a world that feels natural and organic, interspersed with things that... aren't normal.

It's easier to just say, "Gravity works normally, though there isn't Knowledge (Science) to work out exactly why gravity works. There's a sun and a moon that travels across the sky, but there's no Knowledge (Heavenly Bodies) to tell you exactly what they are."

 

[Jack Simth]

Mass is not all there is to surface gravity. You can have a planet with more mass than Earth that has a lower surface gravity than Earth, and a planet with less mass than earth that has a higher mass than earth.

You see, the base equation is something like g = GM/r^2 (G = Gravitational Constant, M = mass of planet, r = radial distance between surface and gravitiational center; already simplified to get the mass of you out). If you have a planet that is four times as massive, but has twice the radius, the surface gravity will be the same. If you have a planet that is 1/4 as massive, but has half the radius, the surface gravity will be the same. It's a density issue.

 

[majustismp15]

E=Earth=1

4ExG
-----
4E^2


4
--
16


1
- Gravity
4


Your planet would need 4 times as much mass to have Earth gravity, and 16 times as much mass to have 4x gravity. It's a weak force (not too many mitochlorians). Plus, any player brought there will drown in the atmosphere, so I hope they don't plan on buying a villa.

 

[irdeggman]

The Laws of Physics totally break down in D&D to begin with so it will only cause you heartache to attempt to apply them sometimes when at other times the rules dismiss them.

I believe it has something to do with "magic".

 

[shilsen]

The Laws of Physics totally break down in D&D to begin with so it will only cause you heartache to attempt to apply them sometimes when at other times the rules dismiss them.

I believe it has something to do with "magic".

I agree, except that I'd add that the laws of physics in the D&D game break down even without magic. The same is true for the laws of many other sciences, such as chemistry or biology. So seeking to apply real-world science to one aspect is generally an exercise in arbitrariness.

 

[wmasters]

I'd ignore the rules of physics and go with a playable game. Otherwise there are issues like terminal velocity from falling off a cliff to worry about, and questions like 'how much energy is actually in this lightning bolt' arise.

 

[Fieari]

And then there are groups that contain IRL physicists who actually enjoy their work, and who house rule physics into the game for fun. But make no mistake about it... physics are house rules.

 

[Ilium]

make no mistake about it... physics are house rules.

So totally sigged.

 

[AuraSeer]

Let's say a campaign world is 4 times as large as earth. We'll just assume the mass is 4 times larger as well, which means their gravitation would be 4 times the power of earth's. Now if a person would enter this world, through a dimension portal or something, he'd have a hard time there. He'd get back problems, amongst other things.

How do you handle these things? (any thoughts)

I've got two ways of handling this, depending on how much science I want in my gameworld.

The more scientific-sounding answer is to fudge the planet's density. If you want a big world with Earth-standard gravity, make it less massive than Earth. Maybe it's partly hollow, or the core has fewer heavy elements, or whatever sounds good to you. You don't have to come up with an explanation or even work out the math if you don't want to. Just declare that the mass is less and the gravity works out to 1g. You can even go the other way, and make a smaller planet that still has normal gravity because its mass is higher.

However, this approach has problems. Once you start trying to make some aspects physically possible, the stuff that still doesn't match will become more obvious. A planet of extremely low density shouldn't be able to support its own weight. On a very small, dense world, you'd have to consider tidal forces. The change in Coriolis effect should change how weather behaves. Add in plate tectonics, the orbits of moons and other planets, plus a whole bunch of other physics stuff, and you wind up with less "realism" than when you started.

The much simpler path is to chuck Newton's law out the window. Gravity is 1g on the planet because that's how the creator deities set it. It could become stronger or weaker if they turned the dial up or down a few notches, and the rules change when you travel to other planes, but that's a Deity Thing that mortals are not meant to comprehend.