XKCD: It's more than a comic

I dunno, a hand-sized object moving as fast as a bullet is going to do some serious damage.

The problem is that, without super-reinforced muscles and bones, you would dislocate or sprain your limbs if you actually threw something that fast. Further, the energy consumed to do something is proportional to the square of the velocity, so running as fast as a cheetah would deplete your body's energy reserves in minutes if not sooner, turning Cheetah Man into Hypoglycemic Man. Never mind the question of whether your lungs would be capable of supplying the oxygen to sustain that rate of energy consumption, or your leg muscles could withstand the force.

edited 27th Aug '16 10:28:39 PM by Fighteer

Sadly, it turns out that we are the way we are, and not stronger or faster or smarter or what-have-you, for reasons...

Intensive training can optimize the body for certain tasks, and we already know how to use technology, such as performance-enhancing drugs, to push that even further (although at a cost). Having "super speed", or "super strength", or any other such power, implies that one's body surpasses the physical limits that we already know to exist. By definition, such a being would be superhuman — that is, possessed of capabilities that are not achievable by an ordinary human. The Required Secondary Powers to make that happen are implied by necessity, or else whoever designed these superhumans is either a Jerkass Genie or a complete idiot.

This is why I sweat the details so much when I write up my own fictional ideas (sadly, unpublished as yet). I feel like I have to deliver explanations that don't just ignore physics or biology as we know them.

edited 27th Aug '16 10:35:26 PM by Fighteer

Yeah, whether the person's muscles and skeletal structure are able to cope with superspeed is another gray area regarding whether it's a secondary power. In some cases the very nature of the "primary" superspeed power makes it a non-issue - for instance, if it somehow applies uniform acceleration across the entire body part, then there are no internal strains caused by the movement; there will only be problems if the body part hits something external. Or if the superspeed is achieved simply by strengthening the body part enough to accelerate at that rate, then there are again no problems - although this is basically then super-strength rather than (pure) superspeed (OTOH, superspeed ought to have a couple of super-strength-like applications, simply by transfer-of-momentum considerations, again up to the issue of whether the speedster's body can handle it. I suppose that bullet idea earlier is one such case).

Energy requirements aren't exactly related to square of speed though. Accelerating a body up to speed v does take 1/2mv^2 of energy as an initial investment, but that isn't related to the power requirements to sustain that speed, which is by far the dominant issue (the minimum initial energy investment to bring a 70kg human to 100km/h is a paltry 6.4kcal). For an ideally efficient method of locomotion this is merely the power required to overcome air resistance, but running isn't too great in this respect. I've looked around and it seems that most sources indicate the power required to sustain some running speed increases roughly linearly with respect to the speed.

Edit: I just realised that theoretically, the power required to overcome air resistance does scale with square of speed at low speeds, and in fact cube of speed at high speeds; because the power required to overcome a force F while moving at speed v is Fv, and drag force scales linearly with speed at low speeds and quadratically at high speeds. I suppose this indicates air resistance is a fairly small portion of the power consumption when running.

edited 28th Aug '16 1:18:52 AM by ashnazg

It's not just about resisting the speed. How many millions of miles has The Flash run? How many miles can any human run without getting arthritis?

The Flash may not be the best example though, seeing as in some continuities he's gone near to, possibly above, the speed of light which introduces a whole new series of problems.

edited 28th Aug '16 12:11:58 PM by FerrousMaelstom

Partially that he must be drawing energy from Another Dimension to power that speed, never mind that a human-size mass traveling at even a reasonable fraction of c on a planet would burn a fiery hole in the atmosphere, demolishing whole cities with the shockwaves.

IIRC the comics just go "but it's okay because speed force."

Pretty much

It acts as a force that more-or-less negates physics when convenient.

Physics don't apply in the human imagination for some reason.

And, conversely, humans find it difficult to imagine what actual physics looks like.

If you want to to this topic seriously though, there's obviously something like "intuitive physics" that humans will apply automatically and find it odd when they aren't present. Just ask an animator about all the little details that need to be gotten just right to even create the effective illusion of movement. There's a deep Uncanny Valley when things don't act in the way our brains expect.

However, your brains are stupid so when things move beyond intuitive physics, often by making them bigger or faster than anything encountered in life, you instinctively apply these same intuitive rules to things that you really shouldn't.

In superhero stories MST3K Mantra applies, physics does not.

A comic in which the human language is a river and we can't control it.

Dang, the one with the dark magic proofs hit home. Computer science is some mystical shit, man.

That alt text was the best part of the comic

Anyone know how to bring up the alt text on Android?

Yup! It displays alt text by tapping the speech bubble above the comic, and also gives a quick link to Explain XKCD for the ones that make you go "huh?".

On Chrome, the alt-text appears at the top of the save image / open in new tab / ... menu that you bring up with a long tap. It doesn't work on the few comics where the image links to something: you'll see the link instead.

An other way is to change the domain name to m.xkcd.com, and use the "(alt-text)" button next to the title.

edited 30th Aug '16 4:45:26 AM by Aetol

I've switched from m.xkcd.com to xkcd2.com, because it saves a tap.

I've discovered that when an image has both the title and alt attributes, Firefox's image properties dialog will only contain the title.

However, its text field will contain the alt attribute if there's no title.

edited 30th Aug '16 5:35:17 AM by Medinoc

OK, I'll try some of that- thanks!

Number of Computers

Oh, logarithmic scales, how I love you.

Why would we be tossing computers at Jupiter in the first place? :S