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38

Okay, from a height of 100 meters, the faller will reach a speed of 44m/s. Human terminal velocity, for a spread-eagle position like skydivers, is 53m/s, so drag is going to play a big role here, especially if he goes spread-eagle. Call it 32 m/s of landing speed. If our hero wants to stop in ten meters from this, assuming roughly constant acceleration, he ...


16

Without having the information to crunch numbers on this... I'm going to call it plausible, but only if the commoners have enough knowledge of physics. What you really need is to absorb energy slowly. For this to happen, your pillows will have to be able to "give" a lot, and quickly. Now, the good news is we are presumably talking about down pillows, as ...


13

Executioner's Sword [This lovely behemoth is a forged replica of the sword Ice from Game of Thrones made by Man at Arms: Reforged. Ilya, one of the build members, specifically refers to it as an Executioner's Sword during the build.] Most swords in the medieval age weren't designed specifically to cut clean through human tissue. They were designed with ...


9

Pick > axe > sword An axe is better than a sword disperses the force too much. Axes concentrate the force on a smaller cutting area although even then it is unlikely. A war pick is even be better since you are looking to do such a small amount of damage to the muscle. A well made, heavy, hardened pick might do it, the fact bone may crack will help in that ...


9

It depends on the mechanism it uses to stick to the ceiling (and on the ceiling material). Using the multiple-tendril mechanism of gecko feet, you can bear a weight of about ten Newton per square centimeter (a mass of one kg in Earth gravity; six on the Moon, and so on). This means that theoretically, and if the ceiling plaster doesn't give way making it ...


9

They can only use as much uranium as they had available, and not all planets will be created equal in this regard. Even something as simple as evolving much later in the life of their planet will give more time for useful fissile materials like U235 to decay into less useful elements. Combined with a lower abundance of fissiles in the protoplanetary disc the ...


7

What you're basically describing here is not a million miles away from the Sail Beam concept by the late Jordin Kare. That idea seems basically sound, and is my personal favourite kind of fast, plausible, hard-science starship drive. There are a few variations on it floating around, but the underlying idea of using a stream of small laser-driven lightsails ...


7

I don't believe he can walk away from this, period. Look at Itmauve's answer--stopping in 10 meters causes 5g of acceleration--done right, this is fine. But can you actually punch 10 meters into a pile of pillows? A quick look in the closet indicates that arranging pillows to make a human-size/shape landing (in a jump you would have extras because you don'...


6

An object between an observer and a light source will affect light coming from the source. https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) In simpler terms, a kugelblitz is a black hole formed from radiation as opposed to matter. (Such a black hole would nonetheless have properties identical to one of equivalent mass and angular momentum ...


5

Yes and no. Sound theoretically could be used to levitate a car, as ultimately sound consists of pressure waves in the air, but the energy needed would mean that extreme sound levels would have to be used. So extreme that anyone riding the car would be immediately deafened. In fact so extreme that their bodies and that of the car would probably be disrupted ...


5

The universal problem of growing cities is not unique, no matter if it is in the sky Have a look at Barcelona: The old medieval quarter of the city had planning principles (or rather lack of planning) that prevented its growth, new development in the modern era favoured matrix style planning (a universal grid) to accommodate extendable development, which ...


5

Yes theoretically, but it would create a dark patch on the bright side, as large as the area you are lightening. Reason for this is that an optic fiber simply transport light with almost (mind this almost, it will become important in the following period you are going to read) no attenuation. But if you want to transport X amount of light from A to B, you ...


4

A 100-meter jump would break current world records for free-fall jumps. I do not believe this would be possible with pillows. Dar Robinson currently holds the world record for the highest free-fall jump in a commercial film at 220 ft (67 meters). That's 33 meters short of the church jump. That's with several safety precautions, practice, and training. ...


4

I found it rather hard to look up various bone thicknesses, but anklosaurus osteoderms seem to have been about 1cm, not very different from pig skulls. And chopping through a pig skull with a one-handed axe seems pretty easy: https://www.youtube.com/watch?v=S3L7M9kj5ls#t=7m00s


4

To be adapted to (and be able to work freely), as opposed to endure; I think you have to re-write biology from scratch using the only known materials that are mostly stable fluids in vacuum, which we use as lubricants for satellites. These are perflouropolyalkylethers (or equivalents). There is actually a whole family of similar-propertied materials. Some ...


4

Hurdles I think you have bigger problems than "nuclear power" if you're trying to force your Thousands-of-Years-Past-Fission Alien Society to use chemical rockets. Why don't they already have: Space elevator (AKA Bean Stalk). A geostationary satellite tethered to the planet below. An elevator goes up and down the tether, making it Much Cheaper to get ...


4

I think that this topic is one that's likely to generate a lot of misconceptions when people answer it, since it's a complicated topic and analogies/explanations that are given by pop science are often not super accurate. So, in an effort to be more accurate I'm gonna try to walk you through some of the actual math. Don't worry if you don't know what ...


3

If you want a really quick rule of thumb for things like this, which assumes no air resistance, and an ideal substance absorbing your fall (which produces the same deceleration at all levels of compression) then you can just use potential energy. The kinetic energy gained in the fall is mgH for mass m, acceleration = g, starting height = H. Suppose an ...


3

I think you would need to specify the force of gravity at the very least to get anything close to a specific answer. Insects grew much larger during the Carboniferous period presumably due to the richly oxygenated atmosphere, but gravity is really the determining factor. The giant bugs seen in classic sci-fi could not exist because they would collapse under ...


3

A micro-sized black hole will be a powerful source of intense gamma rays and interesting particle radiation; that's just the nature of Hawking radiation. A hole which evaporates in a second is emitting zettawatts of EM and particle radiation. A shorter-lived hole will be proportionally brighter, and even if it were travelling at highly relativistic speeds ...


2

This sounds oddly similar to parts of Tomás Saraceno's "Aerocene" art initiative. Heck, he's literally written a book about the subject: The general idea of that art project is to have solar-powered hot air balloons, where the amount of buoyancy is not bound by the gas volume, but rather by the amount of solar energy that can be captured - making the ...


2

Maybe they can't use fission engines, but if they're advanced enough to have depleted all the uranium in their planet after many thousand of years, they definitely have discovered and developed the nuclear fusion. You will need a good explanation on that.


2

Health on the Homeworld Their bodies cannot handle radiation as well as human bodies can. Their ecology cannot handle radiation or other pollution as well as Earth biology can. It could mean that the aliens riding the ship are blinded or permanently made insane by the act of launching. It could mean that the act of launching a ship ruins a city-sized ...


2

Use low temperatures. For a given system, we can tell if degeneracy pressure is important by comparing the Fermi energy $E_F$ to the thermal energy $kT$. if $E_F\gg kT$, the gas is fully degenerate; even $E_F\sim10kT$ will apparently lead to at least partial degeneracy. As the Fermi energy scales as $E_F\propto \rho^{2/3}$, and (non-relativistic) degeneracy ...


1

Early in their development, think ancient egypt, they got inspired by an Oklo-style natural reactor. This gave them a headstart over civilizations using wood as a source of heat. But it also left them with little naturally fissile material remaining and a strong cultural bias for large scale/low energy density nuclear tech. Think more in terms of ...


1

I don't think the changes are incompatible. As it stands we have not found any indication of a pressure that is too high for humans, although there are limits for other reasons. We are vulnerable to too-rapid pressure changes, this is probably quite hard to engineer around as it is going to be basically impossible to stop gases from going into solution ...


1

To alter a human in an way that could survive both incredibly high as well as low pressure, would be impossible. There are to many processes that would need to exist to protect in one state, that would work against it in the other. It's like taking a submarine that's made to keep the water pressure out, and using it in space. However it might be possible ...


1

I think the answer is no, and maybe. ! atm exerts 101 $\frac{kN}{m^2}$ Since sound is a time-varying pressure value about a mean value -- let's assume 1 atm -- the rising pressure would exert an equal force on the ground as on the vehicle by displacing the air. To get enough force to lift an object you need to counteract gravity and then some. As @...


1

The physical process of piling up pillows may be a problem. The people will need to pile up the pillows in a pyramid like shape and the process of stacking may determine how stable it the stack is while people are passing pillows up the stack to the top, as well as how well the stack of pillows cushions the protagonist when he jumps. Did you ever hear of ...


1

there is not enough information given to calculate the number of pillows, like what are the pillows made of and what is their size. and the distance from the jump to where the pillows start, if the stack is 90 meters high then he will not accelerate much before his fall is slowed. given enough of the right pillows it is feasible.


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