My goal is make a world where you cannot fall. So in my world (or at least city) you slow down as you fall so you wouldn’t be going fast enough to get hurt when you land. Im thinking the air is like scales, smooth one way, rough the other, so you can smoothly travel up but there is more resistance when you are going down so you don’t fall too fast. So your terminal velocity would be way lower than normal. People travel by flinging themselves across the city and then they just float down:D I haven’t decided if you’ll still slow down if you just trip, or if objects falling from small heights still slow down, I feel like they would. If we had greater air resistance would that mean that if you tripped would you fall slower than usual or would the resistance be negligible? Another possibility would to have a layer of “elastic air” that would slow you down when you reached it and it would stretch until you reached the ground and exited, then it would spring back up.

This is my first question so let me know if I need to adjust it! I just edited it with more details of what I’m trying to do.

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    $\begingroup$ Maybe look at this amusing footage of people falling in low-gravity for inspiration? $\endgroup$ – KeizerHarm Feb 5 at 9:08
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    $\begingroup$ I don't think there's a definite answer here, as we don't know the details of the air. However, the low gravity example of @KeizerHarm is a good one. You can also think of buoyancy in water or air. Like a half filled helium balloon they can easily travel up and in some cases sideways, while downwards would be much slower. They definitely have a slower terminal velocity and acceleration. $\endgroup$ – Trioxidane Feb 5 at 9:15
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    $\begingroup$ if UP is easy but DOWN is hard, then simple brownian motion of air molecules will result in rapid evacuation of everything from the surface of the planet up into... wherever this strange definition of "up" ends. So will a spinning wheel. the part moving up is unopposed, the part moving down is resisted. End result: instant burnout to the Skies $\endgroup$ – PcMan Feb 5 at 11:54
  • $\begingroup$ KaiserHarm Thanks for a reference, I didn’t realize astronauts tripped that much! $\endgroup$ – Mikey Mabbs Feb 5 at 15:21
  • $\begingroup$ Troxidane Hm I don’t know if buoyancy applies. You would not float or continue going up if you jumped up. I’ll definitely give it more thought though. $\endgroup$ – Mikey Mabbs Feb 5 at 15:31

Could be the entire city is inside a utility fog.


Despite the name, a utility fog is not a fog at all, but rather a solid lattice of 10 micrometer scale robots having 50 micrometer scale arms. Each grain in the network holds the hands of other robots, giving anywhere between 0 and 100 micrometers from one another. With this big a gap, you can breathe and see through it. It’s only slightly thicker than a cloud of pollen. The robotic mesh can re-arrange on command. It can conducts people inside the fog by simply getting out of the way, or enhance mobility by lifting them up. It is powered by ground and data nodes.

A few questions on this stack exchange have envisioned broadly deployed utility fogs for technological “magic” or Pokémon-like monsters in a tiny ball. Utility fogs fit a lot of the bill for a real sci-force field, but the “field” is this metal framework that can rapidly thicken, self-heal, lift someone up, crush them, display imagery, emit sound, and so on.

Your city’s utility fog might allow people to pass through horizontally with ease, but arrest the fall of anyone dropping vertically. In fact, as a safety system alternative to seat belts is utility fog’s initially documented use case.

  • $\begingroup$ 10mm large robots aren't a fog. they'd be like a swarm of locusts. $\endgroup$ – ths Feb 7 at 0:26
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    $\begingroup$ Oops. Micrometers, instead of millimeters . I tried to do the post from memory. Shouldn’t have. Link to fog - en.m.wikipedia.org/wiki/Utility_fog $\endgroup$ – James McLellan Feb 8 at 10:23
  • $\begingroup$ Wow, yes, I like this. I am really trying to blend technology and magic so something like this could really work in my world. $\endgroup$ – Mikey Mabbs Feb 9 at 16:21

Why not just have a thick atmosphere?

To get to a comfortable temperature on a planet like Uranus, you have to go to 50 atmospheres or more of pressure. At such high pressures, air resistance increases, so terminal velocity decreases. Technically, per the formula, it looks like it decreases according to the inverse square of the density, so 49 atmospheres means 7 times lower terminal velocity, I think. (Correct me if I'm wrong ... I know this gets to be a very technical area of science!) Given a planet in a fairly distant orbit with a very thick atmosphere - not as thick as Uranus if we want them walking on land, but thick - we should be able to make it so they don't fall very hard. Note, by the way, that if we reduce a 120 mph Earthly terminal velocity to, say, 12 mph by making the air pressure 100 atm, well, ordinary walking will still take much less force to maintain than is needed to push against gravity.

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    $\begingroup$ At 100 atm, buoyancy would be a significant effect, An 80 kg (176 lb) person would displace about 8 kg of air, so effective weight is 10% less, dropping terminal velocity by about 5%. $\endgroup$ – Gary Walker Feb 6 at 19:05
  • $\begingroup$ Hehe, you're right. I remember looking at this before, but it was on Saturn with a hydrogen atmosphere. :) $\endgroup$ – Mike Serfas Feb 6 at 19:16
  • $\begingroup$ What other effects would that have? Like Gary said, there would be buoyancy to worry about, and I'm guessing things like it would be more difficult to breathe and humans would have to be structured differently. $\endgroup$ – Mikey Mabbs Feb 9 at 16:16
  • $\begingroup$ Most gases are either toxic or have unwanted effects under high pressures. Pure oxygen is toxic under even one atmosphere, nitrogen is narcotic under more than a couple atmospheres. Helium causes high-pressure nervous syndrome. A 49% hydrogen, 50% helium, 1% oxygen mix has been used at 53 atm, but even that's not free of issues. You'd need pretty drastic adjustments to physiology. There'd also be major effects on things like fire (with the oxygen so diluted that even hydrogen can't sustain a flame), or anything that needs to contain vacuum or low pressure gas. $\endgroup$ – Christopher James Huff Feb 9 at 17:30

If you lower the gravity enough, and thicken the atmosphere enough, you can lower terminal velocity until you cannot die by falling off a cliff.


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