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For a fantasy race or for bio-augmented humans, how durable would they have to be to walk away from a 1000ft free fall unscathed? And how would this logically translate to other forms of durability?

Would it make gunfire from calibers like 9mm or .45 entirely ineffectual? What about more powerful rounds like .308 or even .50cal?

Would the force from a bullet that powerful be enough to crack the skull of someone able to survive landing on their head if pushed off a skyscraper?

Normal human durability, and a lot of luck

People have survived terminal velocity falls. In 1972, Vesna Vulović fell over 33,330 ft without a parachute after the plane she was in exploded. She didn't exactly walk away from the fall, however. She spent days in a coma, and was hospitalized for months after that. But she did survive.

Vulović is not the only one to survive a fall that should have killed them. They all had varying degrees of injury, so perhaps it's not quite accurate to say that normal human durability is all that's required if you want to walk away afterwards. But the point is that there are a great many factors involved in surviving a fall, and the height and the body's structure are only two of them.

That said, here are some other suggestions of the types of people who would fall well:

Lighter people

From On Being the Right Size by J. B. S. Haldane:

To the mouse and any smaller animal [gravity] presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only to a hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.

Terminal velocity is a function of (among other things) weight. The lighter you are, the lower the velocity at which you hit the ground, and the easier it is for you to survive.

Wider people

Wingsuit flying is a reasonably popular sport where flyers skydive in a suit with "wings" between the arms and body, and between the legs. These jumps typically end with a parachute, but in 2012, Gary Connery landed a 2,400 ft jump without a parachute, landing on a "runway" of cardboard boxes.

Also, having wings gives you more ability to steer towards softer ground, which is always a plus.

The best enhancements for falling durability are not going to make you bulletproof

Bullets kill by piercing - by applying a large amount of force in a small area, they are able to penetrate the protective layers of our bodies and apply that force to the vulnerable parts of our bodies. That's why bulletproof materials function by preventing the piercing effect and distributing the force over a larger area.

That sort of protection is not going to help against a fall, where the entire area of your body is experiencing the massive forces involved. Conversely, the cushioning and strengthening of the enhancements needed to protect against a fall are not going to do much to stop the piercing effects of a bullet.

Bullet resistance and falling resistance are different from each other. A bullet that impacts some pierce-resistant skin will cause a shockwave to propogate through the body, which will bruise the flesh underneath and potentially cause bloodvessles to break and organs to be damage enough to die off. If you fall from a great height (or are in a carcrash, or have your body accelerated by a car/truck/whatever hitting you), all your organs will suddenly decellerate (or accelerate) and need to be slowed down over as long a distance as possible without ripping the nerves and bloodvessles.

Against bullet, extra fat would help as it would increase the distance the shockwave needs to propagate through before it reaches something vital. Against falling extra fat would mean more velocity for all your organs counteracting the extra distance the organs can now slow down over and increasing the chance the organs will rip out of their place, it's going to kill you faster!

One thing missing in @ArcanistLupus his answer about falling (https://en.wikipedia.org/wiki/Free_fall#Surviving_falls) is that almost all these falls had something break their fall slightly. They didn't really hit the ground with terminal velocity even though they reached terminal velocity at some point in their fall. It's like saying a parachutist survived a terminal velocity fall when he hit the ground.

This leaves 3 answers:

• Make the person lighter without making them smaller. How much I can't say, but this will reduce their terminal velocity and increase their chance of survival.




• Increase the person's surface area. This does mean he's going to need something along the lines of a parachute of surface area somewhere on his body to survive a fall.




• Redesign their internal organs to have more room for the nerves and bloodvessles to follow the organs during the crash. Additionally the organs would need to be suspended with ligaments to allow them to move more and slow down over a larger distance. Possibly the organs could be molded into a bunch of smaller pieces that will each individually be slowed down. This will likely not be enough alone to help you survive.




• as a last option: All of the above.

For a few other options check this similar question I made: Creating a scientifically semi-valid super-soldier, part 3: Physical shock resistance

You d have to look like this

This is a simulation of how you would need to be to resist 100mph car crashes. Free fall is essentially the same problem

Cats frequently survives high falls. How durable are cats?

The cat example suggest it is not the durability (because I guess cats are quite similar to humans in this respect) but how you handle the fall. I would imagine an experienced parachute jumper that had trained on landing without parachute would have quite good chances of surviving (but seriously injured).