The Dresden Files > DF Reference Collection
The science of gravity spells.
narphoenix:
--- Quote from: Ms Duck on June 01, 2013, 01:40:50 AM ---em getting set on fire and burning down later doesn't quite count ya know
--- End quote ---
I know... But still. It technically isn't.
And he did collapse a fair amount of the building. Not all of it, but a fair amount.
Cozarkian:
--- Quote from: Ms Duck on May 31, 2013, 11:54:40 PM ---Gravity is a field.. you 'cancel' it somehow and it 'cancels' for everything.. including the several kilometers of air above the point. Which would have exploded outwards, then gotten drawn back in by your 'mini black hole'.. Im too tired to do the math, but as a WAGstimate I'd put the resulting force well into the atomic bomb category. (the initial explosion would have been more than 1 metric ton per square cm of area changed)(the secondary implosion would have been much, much worse)
--- End quote ---
If anything, if what Harry did is impossible, I think that is more an argument for debunking all of the attempts to apply actual physics to magic. I realize JB/Harry are the source of claiming magic obeys said laws, but in the end, the specific demonstrations in the text trump anything Harry or even JB says. Harry stole the gravity from a large area and transferred it to a small area. It obviously applied to the cars and snow in the area and probably didn't apply to the air (which would likely happen if Harry doesn't think of air as being affected by gravity, because the spell would only do what he thinks it should).
If you want to do an energy calculation, Harry gives us the answer. The amount of force applied to the vamp was equal to the force it would take an anvil to squash the vamp flat cartoon-style. Any excess energy was probably transformed somehow into preventing all of the other negative effects that should have happened, but didn't. Who knows, maybe there are certain things that are possible in physics that we just don't understand. Otherwise, well, I guess it's magic.
SAZ:
I know JB tries to mostly follow basic rules like hot air rises and such, but the DV isn’t real and JB does not hold PhDs in physics, so I tend to cut him some slack some times.
In the DV magic is real and gods can alter reality around them. The SL can make flowers sprout out of Mac’s wooden beams breaking all sorts of natural laws for heaven’s sake. Also it looks like at least some gods were once wizards – so why can’t a wizard alter the reality around a Bvamp and squish it?
Don’t take me wrong; I don’t want to keep folks from having fun and debating what gravity may or may not be, but in fantasy settings like the DV we are already altering reality a lot by having magic and the NN etc… So for me I like to just go with it - particularly if it deals with a subject that is far from set in stone in the real world’s science text books.
The upcoming MM and TT books are other examples of Harry treading where we real world folks don’t have a good grip on things yet – so I’ll just smile and enjoy whatever rules JB comes up with for alternate universes and time travel.
peregrine:
--- Quote from: Ms Duck on June 01, 2013, 12:18:31 AM ---I'm wagging like a dog tail on crack here.. but on the conservative side.
imagine a cone from the center of whatever 'cancel' harry is doing. the radius will be the same as the 'area' that harry hits, then propagate upwards .. what the mass of all that air? (not the barometric pressure, the actual mass)
how much force is it going to create when it displaces?
http://www.pilotfriend.com/training/flight_training/met/atmos_wt.htm
ok, who has got a spreadsheet, some time, and feels ambitious?
;D
--- End quote ---
Yeah, but when it comes to things like that, barometric pressure IS mass. It's the amount of mass whatever column of air of X area would be. And neutralizing gravity doesn't somehow cause it to instantly expand. As we saw when he used it in Changes, it mostly just made them rise up a little bit as their force pushing off of the ground was no longer canceled by gravity. Eliminating gravity doesn't mean that the other air there will suddenly stop holding it in or anything like that. Even if it's in a cone and not a cylinder, the air isn't going to instantly bounce off the air under the effect of gravity, it's still got inertia to deal with. So no superimplodey vacuum, much less an explosion.
Ms Duck:
--- Quote from: peregrine on June 01, 2013, 02:49:02 AM ---Yeah, but when it comes to things like that, barometric pressure IS mass. It's the amount of mass whatever column of air of X area would be. And neutralizing gravity doesn't somehow cause it to instantly expand. As we saw when he used it in Changes, it mostly just made them rise up a little bit as their force pushing off of the ground was no longer canceled by gravity. Eliminating gravity doesn't mean that the other air there will suddenly stop holding it in or anything like that. Even if it's in a cone and not a cylinder, the air isn't going to instantly bounce off the air under the effect of gravity, it's still got inertia to deal with. So no superimplodey vacuum, much less an explosion.
--- End quote ---
Im sorry, but I don't believe that is correct. In a hyperstatic fluid, the force in one direction (aka the pressure) is only a very small part of it; there other factors than just gravity at play (compression, vectors, expansion due to temperature..)
.. and that's the simplified version
as to the inertia question you may be correct but as Knnn pointed out, the forces involved are far larger than most bombs. Your theory would then say bombs can't explode, because of the inertia of the air around them.
:D
this is far enough out of my field I'd rather not tackle the proof, while I had three years of physics in college I'm not an expert, and this is a lot more complex than the Mab or Harry calculations ( for one thing the equation above is only for static, laminar flows. oops.)
even ignoring the air issue, that much of gravity should have drawn in all the mass around it, instead of just squishing down.
oops...
it looked to me like harry just concentrated all the weight of the cars on the vampire, for a fraction of a second. that's several tons of force, more than enough to make vampire pancakes.. and not so much it would wreck half the city.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version