First Lashing and air friction

[Dracnor he/him]

Hello,

I've looked up for this question in the forum, but failed to find a subject that adressed it. If there is one, or a WoB, I'd be glad to

How can a Winrunner use the First lashing for a long time without burning because of friction ? For example, Kaladin flew the entire way from the warcamps to the center of the shattered plains, using multiple lashing. But "flying" isn't the right verb : it's "falling". And falling in air causes friction, a lot of it... especially if you fall at four or five time the normal acceleration (because of multiple lashings).

So... how are they not burning ? You could argue that they are continually healing themselves with stormlight but... what about their clothes then ?

[Honorless he/him]

Perhaps Adhesion, which is the Surge of pressure and vacuum. But that raises interesting questions for Skybreakers.

[Dracnor he/him]

I've done additionnal research since a friend pointed to me that parachuting first involves a free fall phase. They don't need heat shields or equivalent.

However, the free-fall of a parachutist is much shorter than what Kaladin can achieve (the world record of free fall is around 5 minutes, and they had a special suit - but I don't know if that was for friction or cold or oxygen or something else), and it is a fall done at only 1G. 5 Lashings in a direction give you 5 to 6G of acceleration... that's not the same buisness. Also, in that world record of freefall, the sound barrier was actually broken so... does Kaladin breaks it too ?

3 hours ago, R J said:

Perhaps Adhesion, which is the Surge of pressure and vacuum. But that raises interesting questions for Skybreakers.

Oh, nicely seen. Also,it's funny that in the case of air, two surges can manipulate friction : Adhesion (pressure, which is exactly what is friction : a lot of collisions with air molecules), and Friction (obviously, though I don't know how it works at molecular levels - probably just magic). In fact, that's true forevery fluid (if you assume that Adhesion can manipulate any fluid pression, which is a big assumption indeed).

[Quantus he/him]

The heating that happens in orbital reentry isnt going to become a huge issue for Windrunners without really working at it, because they arent being allowed to accelerate in a vacuum where they can exceed the speed of sound as dramatically as space-ships can.  

The bulk of the heat generated during reentry is from shock layers that form when the capsule (which as it comes in is going roughly 25 times the speed of sound) slams into the atmosphere, along with actual physical contact (convective) friction.  Both of those really only become an issue when the flying object in question is going supersonic.  They are at their worst when the object is smooth and blunt (approaching spherical), but get better if the object has more shape and contour to it because that give the air molecules more time to move out of the way.  At it's most basic the speed of sound is the speed of propagation through the fluid (ie air), it's the max speed at which the molecules will act like dominos and bump into each other, which is also how fast sound wave will propagate through it, and how fast air molecules are able to get out of the way of an object.  When something is moving faster than the speed of sound, those molecules can get out of the way fast enough and start getting compressed in strange ways instead, which leads to a lot of the heat generation in reentry.  Once the module slows down below that speed, the temp drops and they start using parachutes and more normal control surfaces to slow down further.  The trick they have to worry about is to not slow down too fast (strange statement to make...) to keep it under 8-9 g's of deceleration, so they dont hurt the crew.  

You normally wont fall faster than the speed of sound, because the drag increases sharply as you get closer to it so you usually reach an equilibrium speed, and require some additional active force before you can shove your way into a supersonic state.  It is possible to go supersonic briefly by falling within the atmosphere, exploiting the loophole that the speed of sound is altitude dependent, so if you reach terminal velocity up there and then dive you may briefly reach a speed that is higher than the Speed of Sound at the lower altitude.  But it would be so brief that they wouldnt have time to build up heat and ignite anything, and the physical wind forces they'd face might be a bigger problem.  It's an issue for spacecraft because they get to accelerate entirely free of a terminal velocity, so when they hit the atmosphere they are going over 17,500 mph (mach 25) and cannot decelerate any faster than about 200 mph per second (without squishing their crew) so they have to hang around slamming through the air at supersonic speeds for a long time.

 

 

[Dracnor he/him]

Okay, thank you very much sir !

Just for the sake of my curiosity, do you have any reference formally explaning the physics (and equations) besides it ?

[Dunkum he/him]

You also have to factor in terminal velocity - that speed at which air resistance counters gravity enough that you no longer accelerate.  for a human on earth this is around 53 m/s (about 122 mph or 195km/h)  which is around 1/6 the speed of sound.  on roshar, it would actually be lower, I think, since they have less gravity than earth, if memory serves.  of course a windrunner can effectively increase gravity for themselves, but doubling gravity won't double terminal velocity, since air resistance is proportional to velocity squared - so doubling gravity should probably multiply terminal velocity by about 2^(1/2) or in other words at a rough guess, wihtout tryign to sit down and do all the math on it, i think that using just the first lashing (and not messing about with adhesion at all) that a windrunner would need 36 lashings or so to break the sound barrier - probably more in fact, and definitely enough to kill them (bodies really can't handle that level of acceleration). basically my point here is that a windrunner would have to lash themselves so many times that they'd die from teh gravity itself long before the heat became an issue (assuming they start from inside the atmosphere - if you start from space, all bets are off)

[Quantus he/him]

15 minutes ago, Dracnor said:

Okay, thank you very much sir !

Just for the sake of my curiosity, do you have any reference formally explaning the physics (and equations) besides it ?

I dont have a particularly good single source with all the equations involved, but these are some of the main principles involved:

 

https://en.wikipedia.org/wiki/Atmospheric_entry#Reentry_heating

https://en.wikipedia.org/wiki/Terminal_velocity

https://en.wikipedia.org/wiki/Sound_barrier

[Karger he/him]

^^The windrunner just hits terminal velocity and stops accelerating.  That would probably be around 100 miles an hour(incidentally that is almost how fast Kaladin falls when going back to harthstone).^^

[Dracnor he/him]

Edit : Dunkum already told everything I'm telling in this reply, but I had somehow skipped over his answer.

 

Thanks Quantus ! The article on the terminal velocity helped a lot =) . It's interesting to notice that in the terminal velocity, there is a sqrt(g) factor. So using multiple lashings to go faster is indeed credible (e.g. going from a simple lashing to a double lashing multplies your top speed by 1.4, and more generally using n lashings instead of one multplies the top speed by sqrt(n) - I probably should plot the graph of how much speed you gain going from n to n+1 lashings, it would be pretty and informative).

(By the way, it's funny to notice that Roshar weaker gravity field (compared to earth) implies that one lashing on roshar grants you less speed than a fall on earth.)

A physicist also pointed out to me that the friction could be entirely counterbalanced by the thermic losses due to the wind : he'll try to compute that.

 

Edited June 16, 2020 by Dracnor
Credits to Dunkum

[thejopen27 he/him]

I'm interested to see Skybreaker vs Windrunner flight. I would imagine that adhesion gives Windrunners a major advantage, especially with their strange ability to be guided by the wind and aided by windspren. I would bet no one is as good as Windrunners over short distances in the air.

[Quantus he/him]

12 hours ago, thejopen27 said:

I'm interested to see Skybreaker vs Windrunner flight. I would imagine that adhesion gives Windrunners a major advantage, especially with their strange ability to be guided by the wind and aided by windspren. I would bet no one is as good as Windrunners over short distances in the air.

Hmm, interesting thought.  Which is more useful, Adhesion or Division? Adhesion can manipulate air pressure and so should easily be able to aid flight, and likely in more diverse ways. But a lot of that aid would likely just come down creating vacuum/low-pressure areas to reduce wind resistance, and Im curious if Division can pull the same trick by Dividing the air in front of the flying Skybreaker?

 

[thejopen27 he/him]

2 hours ago, Quantus said:

Hmm, interesting thought.  Which is more useful, Adhesion or Division? Adhesion can manipulate air pressure and so should easily be able to aid flight, and likely in more diverse ways. But a lot of that aid would likely just come down creating vacuum/low-pressure areas to reduce wind resistance, and Im curious if Division can pull the same trick by Dividing the air in front of the flying Skybreaker?

 

Maybe Skybreakers are faster in a straight line, but Windrunners can make turns and stops faster. Kaladin almost seems to be pushed along by the wind some of the time. 

Edited June 25, 2020 by thejopen27

[GriffinMaze]

Also, magic.

[Dunkum he/him]

3 hours ago, Quantus said:

Im curious if Division can pull the same trick by Dividing the air in front of the flying Skybreaker?

 

I don't think that would work.  based on the coppermind description of the surge of division, it breaks down molecular bonds.  this should release energy and would probably have the effect of pushing back against someone flying through it if they divided the air ahead of them.  It would be like falling inot an explosion - the shcok of the explosion would counter your momentum, not add to it.  might be able to divide air behind them for propulsion, but to get enough force to matter would be pretty dangerous i'd think.  of course, this is all based on a couple sentences form the coppermind, which are in themselves somewhat contradictory (it says it splits molecular bonds, but also ignites, but ignition is itself a form of molecular bonding.  not saying it couldn't happen as an indirect result, given the energy release thing i said, but it's definitely a weird description), so take this with a heaping bowl full of salt.

[Quantus he/him]

4 minutes ago, Dunkum said:

I don't think that would work.  based on the coppermind description of the surge of division, it breaks down molecular bonds.  this should release energy and would probably have the effect of pushing back against someone flying through it if they divided the air ahead of them.  It would be like falling inot an explosion - the shcok of the explosion would counter your momentum, not add to it.  might be able to divide air behind them for propulsion, but to get enough force to matter would be pretty dangerous i'd think.  of course, this is all based on a couple sentences form the coppermind, which are in themselves somewhat contradictory (it says it splits molecular bonds, but also ignites, but ignition is itself a form of molecular bonding.  not saying it couldn't happen as an indirect result, given the energy release thing i said, but it's definitely a weird description), so take this with a heaping bowl full of salt.

Fair point. 

Along those lines, I wonder if a skilled (and durable) skybreaker might be able to add some sort of sustained rocket burn behind them for additional/active Thrust.

[Dunkum he/him]

1 hour ago, Quantus said:

Fair point. 

Along those lines, I wonder if a skilled (and durable) skybreaker might be able to add some sort of sustained rocket burn behind them for additional/active Thrust.

it might be possible, assuming my interpretation of the surge is anywhere close to correct.  I think it would be difficult though, and a lot of the released energy would be wasted, since only a small fraction of it would go to pushing them forward, most would scatter off in all directions unhelpfully.  Still with shardplate (especially living shardplate, which im assuming is probably more durable than the stuff we are used to) they ought to be able to handle it, at least for a time.  but at this point we get into weird questions of fluid dynamics - what happens to the air after you divide it? what happens to the flow of air around you? etc.  my phsycis knowledge doesn't really extend very far into that discipline, so i cant really guess about what would happen there.

[Quantus he/him]

24 minutes ago, Dunkum said:

it might be possible, assuming my interpretation of the surge is anywhere close to correct.  I think it would be difficult though, and a lot of the released energy would be wasted, since only a small fraction of it would go to pushing them forward, most would scatter off in all directions unhelpfully.  Still with shardplate (especially living shardplate, which im assuming is probably more durable than the stuff we are used to) they ought to be able to handle it, at least for a time.  but at this point we get into weird questions of fluid dynamics - what happens to the air after you divide it? what happens to the flow of air around you? etc.  my phsycis knowledge doesn't really extend very far into that discipline, so i cant really guess about what would happen there.

Im curious to see how much control they will actually have when it comes to Division.  One of only times we've seen it be used was Malata burning a fractal pattern into a table.  If they can direct explosions with anything like that kind of detail, there is every possibility they could direct more violent explosions in a vague shape-charge sort of way.  

 

[theTruthshaper]

On 6/26/2020 at 0:10 AM, Dunkum said:

it might be possible, assuming my interpretation of the surge is anywhere close to correct.  I think it would be difficult though, and a lot of the released energy would be wasted, since only a small fraction of it would go to pushing them forward, most would scatter off in all directions unhelpfully.  Still with shardplate (especially living shardplate, which im assuming is probably more durable than the stuff we are used to) they ought to be able to handle it, at least for a time.  but at this point we get into weird questions of fluid dynamics - what happens to the air after you divide it? what happens to the flow of air around you? etc.  my phsycis knowledge doesn't really extend very far into that discipline, so i cant really guess about what would happen there.

As much as I know about chemistry, Divinding the air would probably give rise to this. Which is sort of like lightning, except it will not move and will simply stay there. The ions will probably recombine fairly quickly releasing more heat and light. It will probably make a small explosion. Not viable for sustained thrust, unless of course you have some liquid/gas fuel with you.

[+Oltux72 he/him]

On 16/06/2020 at 5:24 PM, Dunkum said:

that a windrunner would need 36 lashings or so to break the sound barrier

Yes, but he'd enter a transsonic regime and experience extreme buffeting. A human body is definitely not made for breaking the sound barrier at sea level.

On 16/06/2020 at 5:24 PM, Dunkum said:

- probably more in fact, and definitely enough to kill them (bodies really can't handle that level of acceleration).

Technically he is in free fall. He should not feel acceleration (safe from friction) at all.