But is it really the sudden stop?

[malloyd]

Originally Posted by Armin

But what if you didn't remove all kinetic energy; just that along the falling vector. I think that's what RyanW is actually asking about.

Where does that energy *go*? Ultimately what inflicts the damage is some of the energy of the fall gets dissipated inside your body moving and tearing stuff. If the energy outright vanishes, clearly it isn't going to be doing anything to your body.

Of course you are violating two rather fundamental physical laws (conservation of energy and relativity (because slowing everything down at once is equivalent to infinite rigidity, and hence an infinite speed of sound)) to do it, so who knows, maybe the Hounds of Tindalos come out and rip you to bits before you can activate the effect to prevent the universe from terminating.

[Anthony]

Originally Posted by malloyd

Of course you are violating two rather fundamental physical laws (conservation of energy and relativity (because slowing everything down at once is equivalent to infinite rigidity, and hence an infinite speed of sound)) to do it, so who knows, maybe the Hounds of Tindalos come out and rip you to bits before you can activate the effect to prevent the universe from terminating.

You can, of course, do it in a non-instant manner with known effects -- gravity accelerates all parts of an object simultaneously.

[whswhs]

Originally Posted by malloyd

Of course you are violating two rather fundamental physical laws (conservation of energy and relativity (because slowing everything down at once is equivalent to infinite rigidity, and hence an infinite speed of sound)) to do it, so who knows, maybe the Hounds of Tindalos come out and rip you to bits before you can activate the effect to prevent the universe from terminating.

I don't think the latter is necessarily the case. If you activate a body force field, rather than a surface force field, it will act on the entire mass of the body at once, whether the body is infinitely rigid or made of gelatin. Well, you could quibble about the force having a finite velocity of propagation, but that velocity could be c or close to it, and much faster than the speed with which a mechanical impact propagates into the interior.

[RyanW]

I suppose it matters what exactly is meant by "every part."

If it's every molecule (and assuming the effect is smart enough to not instantly reduce the body to absolute zero) there would likely be no damage at all. For example, the fluid in the inner ear would stop right along with the inner ear, so you wouldn't even sense the stop as an acceleration. This would be like an incredibly strong reversed gravity field, which - during free fall - should not (I think) harm you.

If it's every solid(ish) part, it would be akin to a full-body harness, which would prevent whiplash but might do nothing against soft tissue damage. A fast enough fall and our organs might spill out like groceries in a damp paper bag.

I'm spitballing how various effects for a hypothetical magic system might work. Not sure I like the idea of a spell automatically knowing which kinetic energy is heat and which is splat. Must think more...

[malloyd]

Originally Posted by RyanW

I'm spitballing how various effects for a hypothetical magic system might work. Not sure I like the idea of a spell automatically knowing which kinetic energy is heat and which is splat. Must think more...

I don't see that as a problem. It's doing lots of big picture discrimination already - for example picking the "stationary" frame so it knows that it needs to absorb the energy of your motion toward the planet and not the planet's motion toward you. One more bit of distinguishing between net translation and purely local motion is fairly trivial.

[LowManaMovieMagic]

Isn't this what happens when you activate a Bergenholm Inertialess Drive in the Lensman setting? The Bergenholm field effectively zeroes out the falling object's mass and it harmlessly stops as it makes contact with the ground.

[Humabout]

Takig an energy approach (which is a scalar quantity, remember, and thus has no "direction"), your fall converts your potential energy at the top of your fall into kinetic energy during your fall and then some quantity thereof into strain energy that causes deformation of your body. The more you bounce, the more energy remains kinetic and the less goes into deforming your body. I suspect this strain energy is still sufficient to tremendously injure a person, and at the least, it definitely results in a person experiencing far more than just the effects of pulling extra Gs for a millisecond or two. And this is assuming your innards don't bounce around.

[RyanW]

Originally Posted by Humabout

And this is assuming your innards don't bounce around.

If your innards are free to bounce around, it falls under the "full body harness" interpretation. Effectively, you're just trading hitting the ground for hitting an imaginary (and hopefully more forgiving) surface.

Is acceleration at all meaningful in itself? Acceleration trauma is actually more a case of some part of you failing to accelerate, no? Couldn't someone survive any arbitrarily strong force, provided it was applied uniformly instead of only to the surface in contact with the ground/seatbelt/sledgehammer?

[Anthony]

Originally Posted by RyanW

Is acceleration at all meaningful in itself?

It's not even necessarily detectable. Something in free fall is accelerating...

[Ulzgoroth]

Originally Posted by Anthony

It's not even necessarily detectable. Something in free fall is accelerating...

It's not necessarily internally detectable, but there are differences between an intertial reference frame and an accelerated reference frame...