Skydiving, levitation, and the laws of physics. Options

[Jebu]

A mage does some extreme sports and jumps out of an airplane without a parachute. He curls up into a ball, reaching a speed of 300 km/h (250 meters/Combat Turn) before wind resistance stops his acceleration. He then casts Levitate at himself.

The mage has Magic 6, Levitate 5. He rolls five successes. The maximum rate of speed for the spell is 30 meters/Combat Turn. Now, what will happen?

30 m/Turn, but compared to what? Himself, I suppose. So he moves himself upwards at full speed. His falling speed changes from 250 m/Turn to 220 m/Turn, and he can't slow it down any more. Cursing Einstein he is splattered to the ground.

Or can he just stop there in midair, setting his speed to 0? Again, compared to what? There is no absolute speed, just speed compared to other things. Earth is moving 105 000 km/h around the Sun, setting his own speed to 0 compared to Earth would mean he's in outer space very, very soon.

Also, Levitate seems to ignore inertia completely, there's only maximum speed and no mention of acceleration. How about moving at top speed, dropping the spell, and recasting it instantly? You could keep adding the 30m/turn to your speed every recast. Or if you're concerned about the drain exhausting you, just change to force 3 and you'll probably stage the Drain down to nil every time, gaining speed in smaller steps, but reaching any speed you want.

If the spell doesn't nullify inertia, an instant change in speed of 30 m/Turn would feel like driving to a concrete wall at 36km/h. With Magic 8 Levitate 8 it would be 76,8km/h, enough to kill a human.

There's also this thing about the limits of sorcery in MitS, page 47: "Sorcery cannot alter the fabric of the space/time continuum." For all I know, in order to ignore inertia, you'd have to do exactly that.

Ok, it's 3:20 am. Enough said. I'll just post this brainfart and check back later.

[corvusnex]

To be kind to the free-falling mage, I would say that if the mage used his Levitate to try to counter his rate of descent, he would slow his fall by 30 m/turn until his final, controlled speed was within the spell's limits (30m/turn in this case).

If he was falling at 250 m/turn, it would take 8 turns for the Levitate spell to be fully in control of the character's aerial motion.

If you allow this, the Levitate spell is creating an upward acceleration of 6.67 m/s^2 (the maximum for the spell to bring a mage from rest to 30 m/turn in one combat round). This is about 2/3 G, which can be easily handled by normal person.

If you want to be mean, you could just say the free-falling mage is falling too fast for the spell to overcome and the mage dies.

There's 2 options for you.

Corvusnex

Did I remember the formula correctly? X = (Vi)*T + (0.5)(A)(T^2)
So, from a standstill, X = (0.5)at^2, X = 30 m, t = 3 seconds, so a = 6.67 m/s^2

[toturi]

The mage moves at 30m/Combat Turn. Magic overcomes gravity.

[Kanada Ten]

I would say that the levitation speed can act counter to you inertia, in that you could reduce your falling velocity at an acceleration equal to the speed per turn, but that it could not increase your speed beyond it's ability.

So the falling character could reduce the velocity by 30m/turn taking 9 rounds to slow to a stop, but could not increase the rate of falling except during the initial acceleration while the velocity was below 30m/turn.

[Eyeless Blond]

Honestly, if you want my opinion it'd be not to think about things too hard when magic is concerned. In this case, though, if you read through the text again, is teems the speed difference they're talking about is relative to the mage. In other words, it doesn't look like there's any inherent limit to how fast the mage himself travels, so long as the things he's levitating don't move (Magic * successes) m/CT faster or slower than him.

Of course this is kinda overpowered. If you insist on having your magic make a little more sense, revist Levitate so the limit is on acceloration in addition to maximum speed. That way you can impose a limit on the power of a mage levitating himself, which I'm not sure the rules are even really trying to address.

[SirKodiak]

[Jason Farlander]

Right, dont forget that everything in the universe is always travelling at the speed of light. In fact, you can define your current speed as pretty much whatever you want. Also, when you consider the fraction 0/0 (and dont simply postulate its nonvalue out of convenience), you can prove that all numbers are equal. And straight lines aren't really lines, they're curves. So, you dont really need magic to make physics/math make little sense - it does that well enough on its own.

...all that aside, I would say that the levitate spell pretty clearly allows you to ignore gravity, so I dont think its unreasonable to also let it violate laws of inertia. The space/time thing is pretty much there to prevent teleportation, time manipulation, the magical creation of black holes, etc. I'd say its perfectly reasonable to rule that either a) the freefalling mage decreases his speed by 30m/CT, thus taking ~8 1/3 CTs to slow to a halt OR b) the freefalling mage can stop instantly or slow to any speed less than or equal to 30m/CT, changing his direction as he sees fit. I kinda like b), mostly because its cool. But a) might have more appeal to those who want to keep their magic a little more grounded in reality for whatever reason.

[hyzmarca]

Another question is, how much energy does the spell have? Mechanical energy has two componets, Kenetic and Potential.

Kenetic energy is measured by the formula (mass * velocity^2)/2
Potential energy by the formula (mass * height * gravity).

Mechanial energy is conservitive, Kenetic energy and potential energy are freely converted between each other and can only be lost through friction or air resistance. So, the maximum kenetic energy that a levitation spell can provide is equal to the target's mass times gravity, times his maximum height above the Earth.

There are stories of a mage who went to the edge of the atmosphereic envelope, so the spell should be able to provide enough energy to decelerate so long as the skydiver isn't jumping from outerspace. He just can't break 10m/s of horizontal velocity.


Another interperation is that the spell effectivly makes the mage massless, allowing him to accelerate and decelerate instantly without exerting any force, but limited to 10m/s maximum velocity in any direction. In this model, he would instantly decellerate to any speed he desired, within the limit.

A third interperation is that levetated provides an artifical normal force that works against gravity. In this model, the mage goes splat the instant he casts the spell.

There are other interperations, as well. Because magical effectives are based on the caster's subjective beliefs and the vaguries of the spell formula, any model could work. It just depends on the beliefs of the casting mage and/or the person who created the spell formula.

Either way, the 30m/ct is an absolute limit of velocity, not a limit on acceleration or a limit in change of velocity.

[DocMortand]

[hyzmarca]

[RedmondLarry]

[mfb]

it would be pretty stupid for someone to fly a kite in a lightning storm, or bathe in radioactive materials today. the mana warp phenomenon is probably very well-known--hell, that's the first thing i'd try, if i could astrally project. "what's on the moon? i'll go see! urk!" and then, fifty other guys would do the same thing, and eventually someone would realize that flying into space is a bad idea. this knowledge should have percolated all through society by 2060.

[Herald of Verjig...]

Semi-ballistic flight had a barrage of mage deaths early on. After some study, the conclusion was that only astrally active individuals suffered the effects, and only when out of the atmosphere. That's what got the warning labels put on the rockets indicating to stay completely in your meat once the pilot has turned off the "manasphere" light.

Discovery of hazards is done the hard way, but word travels quickly once they are identified.

[mfb]

"please put your meat back in its full, upright position."

[Jebu]

Interesting.. Well, I guess if a situation like that came up in my game, I'd let the spell work as a parachute, slowing the fall, like suggested.

Looking at the spell creation rules in MitS, p. 55, the Manipulation Spell Drain Table lists base drain levels for certain effects. Levitate seems to be a Minor physical change (appearance, motion), base Drain (M), with Physical Spell modifier for Drain Power of +2, for total of +2(M). That seems right for slowing down gradually.

There's also Massive environmental change (control weather, gravity), and I haven't seen any spell examples which use gravity control. Those could ignore inertia I guess. But what else can gravity control accomplish, and what are the limits?

On the sidenote, the spirit power of Movement (SR3, p. 265) can be used at a vehicle. The spirit can use the power each turn to accelerate (or decelerate) the vehicle, and the power description even says similar to the vehicle making an Acceleration or Deceleration test, and also that this change in speed may call for a Crash or Stress Test. This suggests the spirit cannot ignore inertia.

[Kagetenshi]

[Shev]

[hyzmarca]

[John Campbell]

[hyzmarca]

Energy-matter conversions are conservative. The system has the same total of energy both before and after the conversion. The only difference is the form of the energy.

I was specificly refering to non-conservative forces, which cause a system to lose energy.

[Ol' Scratch]

Energy means very little to spells. If it can create mass (Create Food) and energy (Firewall) out of thin air, why is it hard to handle the idea that it can destroy/remove/eliminate it just as easily?

[Rev]

I'd allow it, like people have suggested have the max speed work as a decelleration rate, or something like that.

If I was particularly quick thinking at the time I would probably throw on a +1 or +2 "hurtling toward the ground at high speed" target modifier, depending on whether they meant to do it or did not.

You definitely do not want to jump out of a plane, wait till you are at just the right height to stop yourself then fail the roll. :)

The one I always wonder about is having spirits carry you or items around with thier 3d movement power. Maybe they should only be able to do it with half thier strength or something?