Could a Skimmer run on water?

[JustQuestin2004 he/him]

If a Skimmer stored most of their weight, then got a running start. Could they run across the surface of water?

I'm not a physicist and I can't bothered to try, so I'm asking you guys if this is plausible.

[Treamayne]

22 minutes ago, JustQuestin2004 said:

If a Skimmer stored most of their weight, then got a running start. Could they run across the surface of water?

I'm not a physicist and I can't bothered to try, so I'm asking you guys if this is plausible.

Doubtful. Floating or sinking is not about speed (no matter what the Flash thinks) and only tangentially related to weight - it's about surface tension and water displacement (where more water is displaced for heavier ships). The tread surface of a foot/shoe would never displace water sufficient to float a human body vertically. Even a snowshoe type device is likely to be insufficient, because the size necessary for displacing liquid would preclude function for movement. 

[JustQuestin2004 he/him]

1 hour ago, Treamayne said:

Doubtful. Floating or sinking is not about speed (no matter what the Flash thinks) and only tangentially related to weight - it's about surface tension and water displacement (where more water is displaced for heavier ships). The tread surface of a foot/shoe would never displace water sufficient to float a human body vertically. Even a snowshoe type device is likely to be insufficient, because the size necessary for displacing liquid would preclude function for movement. 

Awww, that's a damn shame. I had an idea for a cool scene in a story that had a Skimmer running on water. Curse you physics! 

[alder24]

1 hour ago, JustQuestin2004 said:

If a Skimmer stored most of their weight, then got a running start. Could they run across the surface of water?

I'm not a physicist and I can't bothered to try, so I'm asking you guys if this is plausible.

Yes, they can. If they are light enough the surface tension will hold them on the surface of the water. There are lizards that can run on water, insects that can stand on it, you can put a needle, paper clip or a razor on the surface - it's all about the surface tension which depends on mass. A Skimmer can stand or run on water, if they can reduce their mass that much (running is easier). 

 

1 hour ago, Treamayne said:

Doubtful. Floating or sinking is not about speed (no matter what the Flash thinks) and only tangentially related to weight - it's about surface tension and water displacement (where more water is displaced for heavier ships). The tread surface of a foot/shoe would never displace water sufficient to float a human body vertically. Even a snowshoe type device is likely to be insufficient, because the size necessary for displacing liquid would preclude function for movement. 

It's not about displacement of water at all. The whole idea of the surface tension is that it holds the object despite its density - a razor blade can be held by the surface tension and it's much denser than water. A Skimmer can change his mass (but not density), so he can get so light that buoyancy won't matter anymore, only water's surface tension.

[JustQuestin2004 he/him]

1 minute ago, alder24 said:

Yes, they can. If they are light enough the surface tension will hold them on the surface of the water. There are lizards that can run on water, insects that can stand on it, you can put a needle, paper clip or a razor on the surface - it's all about the surface tension which depends on mass. A Skimmer can stand or run on water, if they can reduce their mass that much (running is easier). 

 

It's not about displacement of water at all. The whole idea of the surface tension is that it holds the object despite its density - a razor blade can be held by the surface tension and it's much denser than water. A Skimmer can change his mass (but not density), so he can get so light that buoyancy won't matter anymore, only water's surface tension.

HUZZAH! MY DREAMS HAVEN'T DIED!!!

Thanks dude.

[Treamayne]

45 minutes ago, alder24 said:

It's not about displacement of water at all. The whole idea of the surface tension is that it holds the object despite its density - a razor blade can be held by the surface tension and it's much denser than water. A Skimmer can change his mass (but not density), so he can get so light that buoyancy won't matter anymore, only water's surface tension.

I don't think a Skimmer could reduce mass to 10% or less to get a vertical float (and would then probably topple over trying to move).

46 minutes ago, alder24 said:

Yes, they can. If they are light enough the surface tension will hold them on the surface of the water. There are lizards that can run on water, insects that can stand on it, you can put a needle, paper clip or a razor on the surface - it's all about the surface tension which depends on mass. A Skimmer can stand or run on water, if they can reduce their mass that much (running is easier). 

Insect and animals that acheive the feet are doing so through 4 or more points of contact, low weight, distributed across a large "surface area" of water. In the case of the lizards and frogs, it also includes enlarged foot pads that both distribute weight and trap bubbles of air between the water's surface and the bottom of the foot. In the case of the bipedal Basilisk Lizard, it travels at 1.5 m/sec for 2-3 seconds of super-surface travel time before sinking. So, in a human, you would not only require something like the specialized fringes on their feet, the ferring would have to also have F-Steel for speed (analysis):

Quote

Think you could do something similar with special shoes shaped like a basilisk lizard's feet? Unfortunately, gravity would make this an impossible feat. To run on water like a basilisk lizard, a 175-pound human would have to run at a pace of about 65 miles per hour!

@JustQuestin2004 Maybe on all fours. Crawling - and likely requiring hand and knee pads for larger surface displacement. . . 

 

Edited March 19, 2024 by Treamayne
SPAG

[RoyalBeeMage he/him]

19 minutes ago, Treamayne said:

Think you could do something similar with special shoes shaped like a basilisk lizard's feet? Unfortunately, gravity would make this an impossible feat. To run on water like a basilisk lizard, a 175-pound human would have to run at a pace of about 65 miles per hour!

what about a skimmer with special shoes? at that point, they wouldn't need to worry about gravity as they can massively reduce their weight.

[JustQuestin2004 he/him]

17 minutes ago, RoyalBeeMage said:

Think you could do something similar with special shoes shaped like a basilisk lizard's feet? Unfortunately, gravity would make this an impossible feat. To run on water like a basilisk lizard, a 175-pound human would have to run at a pace of about 65 miles per hour!

What about if they were also an A-Pewter/F-Iron Twinborn, would the extra strength and speed plus reduced weight help?

[Treamayne]

25 minutes ago, RoyalBeeMage said:

what about a skimmer with special shoes? at that point, they wouldn't need to worry about gravity as they can massively reduce their weight.

45 minutes ago, Treamayne said:

Maybe on all fours. Crawling - and likely requiring hand and knee pads for larger surface displacement. . . 

^That's why I mentioned that.^

If you have ever used snowshoes, you can understand how "special shoes" with enough surface area for weight displacement would be difficult to use quickly - and I think even reducing to 30-40% weight would still require "shoes" so large that movement becomes impractical - and I am unconvinced that a skimmer could reduce below 25-30% - not to mention storing F-Iron does nothing to reduce the weight of your clothes and gear. 

Snowshoes require a very controlled and deliberate pace IME, and I would expect that aspect to be amplified by crossing a liquid medium. 

7 minutes ago, JustQuestin2004 said:

What about if they were also an A-Pewter/F-Iron Twinborn, would the extra strength and speed plus reduced weight help?

I don't think strength helps - and may even make things worse, as pushing too strong while moving will only make it more likely to break the surface tension of the water, not reinforce the surface tension to provide floatation.

[alder24]

1 hour ago, Treamayne said:

I don't think a Skimmer could reduce mass to 10% or less to get a vertical float (and would then probably topple over trying to move).

It's not about floating due to buoyancy, it's about being light enough to not break surface tension. You can store so much mass that you can actually float in the air, or imitate a microgravity environment - I think walking on water is easier than floating.

Spoiler

Questioner

So if someone is storing weight-- Feruchemy-- Can you store enough that you can actually float like a balloon?

Brandon Sanderson

Uh, your clothing and stuff will still have weight.

Questioner

If you were, like, completely naked and just *unintelligible* your hand up a wall, you will?

Brandon Sanderson

Yes. You will-- You could float, yeah. That's-- I mean, you could get your weight so low that it's basically like being in microgravity, which is...q

Questioner

Like 99%? Like a vacuum balloon?

Brandon Sanderson

Yeah.

Calamity release party (Feb. 16, 2016)

Yes, it would be hard to get a hang of it, you would lose balance quite often at first, but it's still possible. It would be a very weird feeling, but running on water would be easier than just standing. 

1 hour ago, Treamayne said:

Insect and animals that acheive the feet are doing so through 4 or more points of contact, low weight, distributed across a large "surface area" of water. In the case of the lizards and frogs, it also includes enlarged foot pads that both distribute weight and trap bubbles of air between the water's surface and the bottom of the foot. In the case of the bipedal Basilisk Lizard, it travels at 1.5 m/sec for 2-3 seconds of super-surface travel time before sinking. So, in a human, you would not only require something like the specialized fringes on their feet, the ferring would have to also have F-Steel for speed (analysis):

If the question was can a person run on water then you are right. But the question is can a guy that has a magical ability to reduce his mass down to a feather run on water. Yes, yes he can. Magic solves all your problems. As you store mass your mass to surface area ratio increases dramatically - you can walk, or even stand on water without being a Steelrunner, just store enough mass. There is nothing else a Skimmer needs to do. 

https://www.youtube.com/watch?app=desktop&v=6jyoBp2dBAo - here is how you calculate surface tension. By my understanding it should work the other way, instead of pulling the object away from water until the tension breaks, push it until it submerges underwater. The surface tension of water is 72mN/m - that means as long as you stay below that value, you will be held by the surface tension of water. And because the equation for it is v=F/2L (for something like a wire), where F=m*a, where m is maas, a is gravitational acceleration for an object at rest, you just need to decrease your mass enough to get that tension value below the breaking point. Disclaimer, I'm not very well versed in that topic, so my understanding of this is flawed. But mass is a big factor in surface tension.

Here is another, better example with razor blades - https://user.engineering.uiowa.edu/~fluids/archive/HW/Solutions/2007/Ch01/01_084.pdf. The important part to see here is that for an object to stay on the surface, you need to find equilibrium between its mass and the resultant surface tension. The single edge blade was around 4x  heavier and 1/4 shorter than the double edge blade and that's why the single edged blade sank while the double edge blade didn't. A Skimmer can reduce its mass until he finds that equilibrium. That's it. There is nothing else needed. No buoyancy, not even running (but while running you don't have to reduce your mass that much, just like that lizard).  

[Treamayne]

6 minutes ago, alder24 said:

It's not about floating due to buoyancy, it's about being light enough to not break surface tension. You can store so much mass that you can actually float in the air, or imitate a microgravity environment - I think walking on water is easier than floating.

Copy all, I had not seen that WoB. Though it begs the question - why are other attributes capped at storing about 80%, but F-Iron can store 99%?

Just to make sure we are on the same page - do we agree that Storing 80% would be insufficient - but storing over 90% might work (as long as however you manage your footwear does not break surface tension in the act of taking steps)?

[alder24]

17 minutes ago, Treamayne said:

Copy all, I had not seen that WoB. Though it begs the question - why are other attributes capped at storing about 80%, but F-Iron can store 99%?

Probably because other attributes store your physical things like muscle mass and you need some bare minimum of that to function at all, while iron vaguely stores mass, which doesn't decrease your size, nor your density, nor your fat, muscles or anything physical. It's the weirdest attribute to store because it has to work weird as mass is essential for basically everything. 

19 minutes ago, Treamayne said:

Just to make sure we are on the same page - do we agree that Storing 80% would be insufficient - but storing over 90% might work (as long as however you manage your footwear does not break surface tension in the act of taking steps)?

Can't tell if those numbers are correct, someone smart would have to do precise math. But you need to store a lot of mass to stand on water, or little less than a lot but with running. Either way you need to store a lot.

[Quantus he/him]

The other aspect aspect of the physics of all this is the skimmer's Foot speed when striking the water.  Surface tension equilibrium is how you'd go about calculating what it would take to stand still on the water.  But for running it's about the force equilibrium of the impact on the surface of the water, so you have to look at the Viscous Dampening aspect of the fluid.  The short version is that water resist motion of an object relative to the velocity that object is travelling; it's why water is no better than concrete from a high enough fall.  If the foot has favorable geometry (more concave than convex, mainly) and it strikes the surface of the water fast enough, the water will push back just as much as a solid surface would, and you can traverse the water. While weight and surface area of the foot will affect the force to keep the person from falling toward the water, it would be modelled as a series of strike impacts that is propelling the person upward&forward.  That's how a Flash-style speedster runs on water, even with full human weight.  

Edited March 19, 2024 by Quantus
grammar...

[Colors]

Math...it gives me a headache. 

[Quantus he/him]

Well, it's not NOT hacking the source-code of reality, so headaches seem justified.  

[Colors]

1 minute ago, Quantus said:

Well, it's not NOT hacking the source-code of reality, so headaches seem justified.  

A fair point. 

I was cursed to be born right-brained  

 

On-topic. Would making yourself that much lighter make it extremely difficult to run at all? Air has resistance too after all. 

Edited March 19, 2024 by Colors

[Etedbert he/him]

2 hours ago, Colors said:

A fair point. 

I was cursed to be born right-brained  

 

On-topic. Would making yourself that much lighter make it extremely difficult to run at all? Air has resistance too after all. 

You’re right! Given that running is (very simply put) just an application of force against the ground, with the equal opposite reaction propelling you forward, and since force is a product of mass and acceleration with such a low mass, you’d have a hard time getting much speed, to go enough force to move fast you would need to be able to move your legs crazy fast.

some arm chair math:

rough low ball estimate of force put out by a single footfall of a runner is 1200lbs for 150lbs individual (source: http://www.aecreatingelite.com/blog/2019/12/17/ground-forces-of-jumping-amp-running#:~:text=The repeated stress would be,for the 150 lb person.)

in better units, that’s 5,337 neurons, emitted by a 68kg person.

that means their foot is accelerating at ~78.4 m/s^2. (5,337/68)

if we bring their mass down to 1% to reach the “microgravity” state Brandon mentioned here

Spoiler

Questioner

So if someone is storing weight-- Feruchemy-- Can you store enough that you can actually float like a balloon?

Brandon Sanderson

Uh, your clothing and stuff will still have weight.

Questioner

If you were, like, completely naked and just *unintelligible* your hand up a wall, you will?

Brandon Sanderson

Yes. You will-- You could float, yeah. That's-- I mean, you could get your weight so low that it's basically like being in microgravity, which is...q

Questioner

Like 99%? Like a vacuum balloon?

Brandon Sanderson

Yeah.

Calamity release party (Feb. 16, 2016)

1% of 68kg is 0.68kg (gotta love quick decimal math) To get the same force output of 5,337 N, you’d need to accelerate your legs at… ~7,848.5 m/s^2

…wow. That’s reaching hypersonic MACH 22-23 speeds within a second.

TLDR:

to effectively run while the skimmer had their weight down low enough to walk on water, they’d need to be moving their legs at hypersonic MACH 22-23 speeds.

without some form of healing, or reinforcement, their body, or at minimum their legs would be instantly blown to shreds from heat and air resistance.

[Returned he/him]

Also a potential item of interest: you would need an ironmind large enough to store a sufficient amount of your mass during your effort to run across the surface of the water, and you cannot magically alter the weight of that item. Depending on the amount of time you want to spend not sinking and the amount of mass you need to shed, the weight of the ironmind could potentially undermine the whole effort. Though the examples we've seen suggest to me that you can probably use a pretty small amount of iron to store sufficient mass.

I bet you could "pulse" your mass so that you have an appropriately small amount while descending towards the water's surface, stop storing weight to allow good-enough running motion of legs, store again for contact with the water's surface, and then stop storing once more to overcome the air's resistance as you move forward. It seems like a pretty precise operation, though, and I feel like you'd steadily lose velocity as you moved forward and wouldn't be able to recover much of it.

Edited March 19, 2024 by Returned

[Colors]

18 hours ago, Etedbert said:

You’re right! Given that running is (very simply put) just an application of force against the ground, with the equal opposite reaction propelling you forward, and since force is a product of mass and acceleration with such a low mass, you’d have a hard time getting much speed, to go enough force to move fast you would need to be able to move your legs crazy fast.

some arm chair math:

rough low ball estimate of force put out by a single footfall of a runner is 1200lbs for 150lbs individual (source: http://www.aecreatingelite.com/blog/2019/12/17/ground-forces-of-jumping-amp-running#:~:text=The repeated stress would be,for the 150 lb person.)

in better units, that’s 5,337 neurons, emitted by a 68kg person.

that means their foot is accelerating at ~78.4 m/s^2. (5,337/68)

if we bring their mass down to 1% to reach the “microgravity” state Brandon mentioned here

  Reveal hidden contents

Questioner

So if someone is storing weight-- Feruchemy-- Can you store enough that you can actually float like a balloon?

Brandon Sanderson

Uh, your clothing and stuff will still have weight.

Questioner

If you were, like, completely naked and just *unintelligible* your hand up a wall, you will?

Brandon Sanderson

Yes. You will-- You could float, yeah. That's-- I mean, you could get your weight so low that it's basically like being in microgravity, which is...q

Questioner

Like 99%? Like a vacuum balloon?

Brandon Sanderson

Yeah.

Calamity release party (Feb. 16, 2016)

1% of 68kg is 0.68kg (gotta love quick decimal math) To get the same force output of 5,337 N, you’d need to accelerate your legs at… ~7,848.5 m/s^2

…wow. That’s reaching hypersonic MACH 22-23 speeds within a second.

TLDR:

to effectively run while the skimmer had their weight down low enough to walk on water, they’d need to be moving their legs at hypersonic MACH 22-23 speeds.

without some form of healing, or reinforcement, their body, or at minimum their legs would be instantly blown to shreds from heat and air resistance.

I may be bad at math, but I'm usually pretty good with understanding the effects it describes  

The heat radiated by limbs moving that fast could also effect the surface tension I'd assume, although maybe it would be happening too fast for the heat to have much of an effect? The warmer water is the less surface tension it has as I understand it. 

The stillness of the water would also have an effect on how easily you could walk on top it as well, correct? I assume the surface tension on a completely still body of water would be stronger, or at least more stable and less prone to being broken than water that is rough with waves or turbulent rapids. 

 

Which begs another question.....if you were to walk on top of a body of water that is smooth, but moving (ex. a large, non-turbulent river) what would walking on that be like? Would it be like walking on a giant treadmill belt? 

[alder24]

1 hour ago, Colors said:

The heat radiated by limbs moving that fast could also effect the surface tension I'd assume, although maybe it would be happening too fast for the heat to have much of an effect? The warmer water is the less surface tension it has as I understand it. 

Not a factor. Water is great at dissipating heat and you're in contact with it for just a fraction of a second while running - too fast to heat it up with your body temperature. 

1 hour ago, Colors said:

The stillness of the water would also have an effect on how easily you could walk on top it as well, correct? I assume the surface tension on a completely still body of water would be stronger, or at least more stable and less prone to being broken than water that is rough with waves or turbulent rapids. 

Looking at the example with razors, the angle between the water level and the force of surface tension matters. More stable water would be better. 

1 hour ago, Colors said:

Which begs another question.....if you were to walk on top of a body of water that is smooth, but moving (ex. a large, non-turbulent river) what would walking on that be like? Would it be like walking on a giant treadmill belt? 

Seems like it. 

[+Lewis Nethur He/Him]

Sazed stores mass at one point in order to gently glide down a cliff face, which implies nearly 100% reduction with gravity only pulling on his wesrables. Air and water are both fluids. 1000% skimmers can walk on water, they don't even need to run if they have good control, they should be able to stand on it.

They might have to be naked in order to do it though. 

[DrPhysics he/him]

On 3/19/2024 at 3:59 AM, JustQuestin2004 said:

If a Skimmer stored most of their weight, then got a running start. Could they run across the surface of water?

So, I'm super late to this party, but the answer is yes. A group of Italian researchers (sorry if the link is paywalled- I can't tell if it's free or if I just have access through my University) figured out that you could with flippers. In case it is paywalled, I attached their video of someone doing it under simulated low gravity (aka help up by a fancy rubber band). 

Also, here is the important bit:

Quote

As predicted by the model, our experiments show that the highest gravity for which a person can run on water is about 0.22 g_EARTH. All subjects were able to avoid sinking at 10% g_EARTH, and a decreasing number of them were successful at higher gravities (Fig. 2, bars). We also found that the subject-chosen stride frequency and maximum vertical speed of the knee were both independent of the gravity level (see Table 1). Figure 3 shows the time-course of the vertical position of the markers located at the hip and shoulder, from which the position of the center of body mass was obtained. Equation 21 produced the curves shown in Figure 4.

So, as long as they dropped their mass to less than 20%, dropping that mass doesn't slow them down, and they have flippers (or something similar), they could run across water for 7-8 seconds (not in the quote), and the time gets longer for lower gravity. The forces scale like the area of the foot, so if they were in regular feet only it would be possible at 3% of their normal mass, but at that point buoyancy and air drag start mattering a lot more and the math gets weird.

Edited October 28, 2024 by DrPhysics