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I have read dozens of books where gravity magic is a thing. It ocurred to me, while reading one of these stories, that every version of a gravity magic spell that I have heard of, is missing something, namely they dont consider the effect of the spell on fluids in the environment like air or water.

A typical example would be a spell where the caster creates a invisible plane where the acceleration due to gravity is a constant with its vector perpendicular and pointing towards the plane. This is demonstrated in the stories when the spell is cast on the ground, crushing an opponent, or horizontally throwing an opponent, etc.

Realistically though, if a gravity spell was cast on the ground, the column of air over the gravitational plane would also be affected.

My initial thoughts are the air column would fall and compress, which would cause the air to heat dramatically, then a vacuum would form where the air was leaving creating extremely high winds which would could eventually form a fire tornado. Where would it end though? Could it cause a fire hurricane? Would it get hot enough to vaporize rock and bore a tunnel to the Earth's core?

So my question is, what effect would a gravity spell have if its plane of attraction was a 20' diameter circle placed on the ground that increased gravity in a vertical column by 1g and it could last 1min, 10min, or an hour before expiring?

Edit:

  1. I wasn't trying to cast shade on any other authors for their flavor of gravity magic, I just wanted to explore some possibilities.

  2. This gravity magic works by adding a gravitational force to an area except instead of pulling omnidirectionally to a point it pulls unidirectionally towards a plain. The portion of any object that intersects a line perpendicular to the spells plain starting at the plain and going off into infinity in the opposite direction of the gravitational pull of the plain would be in the spells aeea of effect. The magnitude of the acceleration would fall off as the distance above the plain is increased in the same way the magnitude of acceleration due to earths gravity is reduced as you go further away from the surface of the earth. The magnitude of the force, shape of the plain and duration of the effect can be modified in the spell. For this question I restricted the spell to a 20' circle on the surface of the earth that adds 1g of acceleration in the same direction as the acceleration due to Earth's gravitational pull at that location. I also asked the effects for a 1min, 10min, and 1hour duration under the assumption the spell would cause weather effects that would be pretty different based on the spells duration.

  3. I was hoping for an answer that would take into account the pressure, volume, density equation: PV=nRT, where P=pressure, V=volume, n=number of moles of gas, R=ideal gas law constant, and T=temperature. Answering that would depend on things like how the turbulent boundary layer that would form along the surface of the affected cylinder of falling air would effect the maximum pressure of that air cylinder, how doubling gravity for just that cylinder would affect the terminal velocity of the air, etc. Knowing the pressure, temperature and velocity gradients in the spells direct area of affect should also shed some light on weather affects, etc.

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    $\begingroup$ This is entirely dependent upon the the specific rules for your gravity magic in your world. Since you don't describe your rules for your specific spell there is no way for us to answer this question in any objective way. $\endgroup$
    – sphennings
    Jul 31 at 23:10
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    $\begingroup$ WB.SE is not really a place that is concerned with nit-picks concerning some other writer's allegedly flawed magic. You don't need our permission to think that some writer's idea of gravity magic is not sufficiently realistic, and it's not our place to give you that permission even if you did. $\endgroup$
    – Tom
    Jul 31 at 23:13
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    $\begingroup$ Realism and magic don't really mix. That said, gravity changes based on altitude and depth on Earth and it also doesn't lead to big fire tornadoes. $\endgroup$
    – ITM_Coder
    Jul 31 at 23:16
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    $\begingroup$ VTC needs more details: I don't see anything wrong with asking about the detailed consequences of the effect of a spell (for the sake of your own imaginary world, right?...) but we already have a falsehood that we're dealing with: the interface between reality and magic that created the change in gravity in the first place. Who's to say that the effects of that field don't extend beyond 10' above the ground and not below it at all? Well... you. (And that's @sphenning's point.) $\endgroup$
    – JBH
    Jul 31 at 23:24
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    $\begingroup$ ...You need to tell us much more about the nature of your magic, its limitations, and both how and where it's being used. Is it used inside a cave? It would likely collapse the cave. Is it used during a rainstorm? Is it used in mountains in the fog or in the middle of a herd of wildebeests? Do you want it to act like a "gravity plate?" Does the field only pull down, or also up from below to the "plate?" We're missing far too many details for an effective answer. What do you want to get out of this? Because we're not a discussion forum and don't explore ideas. We answer questions. $\endgroup$
    – JBH
    Jul 31 at 23:27

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Turbulence:

I think you are overthinking the effects - besides the total collapse of reality as the laws of physics are broken.

With an increased gravity force pulling down, you would simply achieve a downdraft. gasses in the column would be effectively heavier than the gasses around it, and they would sink. Of course, the gravity isn't affecting the pressure, so the gasses would tend to rapidly compress out of the column as the air moves down. The gasses throughout the column would pull fairly gently on the air around to fill the space as the gasses sucked in and then were blown out due to pressure.

There would be almost nothing happening to the ground, except the effects of wind and turbulence. Any heat generated by friction would rapidly diffuse. Many surfaces on the Earth (like where a truck parks) experience temporary increases in weight, so ground deformation would me slight at best.

It's a lot more fun if the column is the other way, but still not Earth-shaking.

You would have a dirty column of air shooting upwards quite a bit like a tornado. air would be both sucked in (especially at the bottom) and blow outwards to adjust the pressure of the air in the column with the air surrounding it. At the top, near space, the pressure differences of the lower and upper columns would cause very little loss to space as the gravity tried to accelerate gasses towards space, and the denser gasses from below diffused outwards to adjust pressure. It would likely start to rotate from the Coriolis effect, and might even visually be indistinguishable from a very out-of-place tornado. Friction would generate some heat, but not enough to make a huge difference given the level of air mixing that would likely be going on up and down the column.

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An exotic location for your column (like a lake or river of lava) might have some specialized effects, but I'll assume a more standard soil covering rock (eventually). The ground and loose soil would rocket upwards and scatter in all directions as the violently mixing air blew it out of the gravity column. but consider areas where there are tunnels and overhangs of dirt and stone. the cohesion of the matter is high enough that a fair amount of it would stay put despite the change in gravity.

  • Some strange chemistry might occur at the very edge of the column, as individual molecules are torn by conflicting gravity fields affecting different individual atoms. But the strength of the bonds in most molecules would likely be able to resist the effects. Still, certain types of molecules (especially very long ones) could experience exotic effects. It is entirely possible that passing in and out of the column could kill an animal, as all the molecules in its body are individually stressed by 3G's of shear (one down, two up to cancel the gravity, in the case of the reversed gravity).
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    $\begingroup$ You have reversed the OPs question and made the gravity point upwards in opposition to the Earth. Which would be an awesome thing and nowhere described more awesomely than in [H.G.Wells The First Men in the Moon. ](en.wikisource.org/wiki/The_First_Men_in_the_Moon/Chapter_2) linked here for your convenience. But the OP wants gravity crushing down, in addition to that of the Earth. $\endgroup$
    – Willk
    Jul 31 at 23:32
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    $\begingroup$ This is funny. I was struggling to understand why everything would be going up. Was I missing some strange convection current effect or something? Nope. $\endgroup$
    – n00dles
    Aug 1 at 0:30
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    $\begingroup$ @Willk Misread the question, but super-easy to fix. $\endgroup$
    – DWKraus
    Aug 1 at 1:25
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It depends on whether your gravity spell pulls downwards towards a plane, downwards towards a point or (amusingly) inwards from a spherical area.

  1. Gravity spell pulls downwards towards a plane. This is the simplest scenario and the one which is usually implied. If gravity is increased in a single direction towards a flat surface, air will also be pulled towards the surface but will be pushed sideways out of the area of effect by the continual torrent of air being sucked into the upper area of the spell. This means that if a person is subjected to an extra 0.5 gravity, they would also have to contend with the continual downwards flow of air with the same extra 0.5 gravity force behind it - which would essentially double the "gravity" pushdown on the person through the added continual air pressure. No odd effect with liquid in this scenario.

  2. Gravity spell pulls downwards towards a point. This is where things get wonky. If you stood on a planet with 1.5* the gravity of earth, you could easily predict the added difficulty of breathing or circulating blood in the human body as humans are essentially up/down pressure systems. If a human is pulled inwards towards a point however, you could land up with the situation where half his body (on the left of the spells center) experienced gravity towards the right while the other half of his body (on the right of the spell's center) experiences gravity towards the left. Lord knows the damage that sort of inconsistency is going to do to your internal blood flow. Additionally, if the lungs on the affected individual are near the center of the gravity well, they going to find breathing in very easy and breathing out very hard as air wants to move towards the center of the gravity but not away form it - this in comparison to simply standing on a high gravity world where breathing in and out is made equally harder. I will add though that if air is being drawn inwards towards a point this will result in the air heating up.

  3. Gravity is pulled inwards from a spherical circumference. I'm not sure what to say here besides "let loose the clowns". If the gravity spell is strong enough, the ground itself should push upwards as the affected adventurer is pressed down. As the top half of the spell will be filled with air and the bottom half with compressing ground however, i think its fully possible that the compressed ground will crumble upwards (being under pressure and having no other direction to move in) and then be pushed inwards again. In this scenario, the effect of the spherical gravity spell will be to compact the target in a sphere of earth - which while cool, probably isn't an effect one would expect from this school of magic.

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  • $\begingroup$ The question is "what effect would a gravity spell have if its plane of attraction was a 20' diameter circle placed on the ground that increased gravity in a vertical column by 1g and it could last 1min, 10min, or an hour before expiring". It is very clear from context that its' 1g up to the upper border of the atmosphere at least. DWKraus already answered it. Mild downdraft at worst. Where did you get "double the gravity pushdown"? It doesn't seem to follow from anywhere. $\endgroup$
    – D'Monlord
    Aug 2 at 14:33
  • $\begingroup$ Why do you assume there is less force applied to the air in the area of the spell then solid objects? Air is a liquid and it pushes down on you. Compress the air and it becomes more liquid like. It may not double the pressure of the gravity spell, but any gravity spell strong enough to immobilize a human is going to have a far greater air pressure increase then a mild downdraft. $\endgroup$
    – Alot
    Aug 3 at 7:41
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We don't really know, because gravity is not a force.

Since it is tagged science based and physics - I will attempt to answer as close as possible to our current understanding of Gravity in physics terms.

Gravity is not a force. It is the bending of spacetime towards regions of higher mass. What does this mean? It means that all objects that have trajectories 'at rest' (ie. with no other forces acting on them) move initially linearly through spacetime coordinates. They then 'appear' to bend in space and time only as spacetime itself is bent to a region with higher mass and energy.

One way to look at it is our Moon is actually travelling in a straight line because Gravity is not a Force - it is actually resting. What is happening is the Moon's trajectory 'appears' to bend around the Earth because Earth is within a region of higher mass, and thus has a bent spacetime around it such that the Moon's straight line is a now a circle (ie. an orbit).

No force is acting on the Moon. No energy is being applied to it. The Earth is not 'pulling it'. The Moon is at rest and does not experience acceleration. Only if we apply rockets (ie. a force) to the Moon will it experience force.

This means that on Earth, we feel heavy when we sit on a chair not because a force is pushing us down, but because the chair is instead pushing us up. The Earth and chair actually consists of atoms, each repelling each other. It is actually the electromagnetic repelling force that is causing us to 'feel' gravity, which is actually a push upwards from our chair.

So your magic of 'plane of attraction', 'gravitational force to an area', makes no sense as there is no 'attraction', there is no force due to gravity. All objects in the universe are at rest. The only forces experienced by objects are electromagnetic ones (or Strong & Weak nuclear forces too which for brevity we shall ignore).

So I propose to accomplish your spell, you are in fact halving the power of the electromagnetic force in that region instead. This would reduce the repelling effect of all electrons within that region, and cause each objects trajectory to be less influenced by that force, and thus revert more to its original 'at rest' trajectory which would likely be towards the Earth, as this is a region of higher mass.

Of course, this would also cause havoc with electrons and photons, and likely have profound effects in all areas of physics, not just newtonian but also including implications for particle physics interactions, nuclear physics and chemistry. To answer your question, I imagine that although objects would 'appear' to accelerate towards your magic 'plane', at the very least electrons would be less bound by their nuclei and objects affected by your field become odd indeed, being perhaps ejected. Although their trajectory would be more towards the 'ground', for 1 hour all objects may also 'explode' (although I am just guessing there - I would imagine a shower of free electrons, light and energy).

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