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Super speed is an ability commonly seen in fiction often used by powerful characters and extremely fast characters like the flash. However, explaining all of super speed in a single post would be too broad for this question to work so I am creating a series for this question to work instead.

This question is about how a humanoid could accelerate to Mach speeds without the use of biological engines and hyper dimensional alien tech.

Due to this question being about the acceleration part of super speed and not the other parts of it (perception,friction resistance, g force adaptation)

Here is what I think this character should be able to do.

  • Move at speeds up to Mach 5 and above 500 mph.
  • Be able to accelerate other appendages at such high speeds
  • Be able to accelerate in a 1 second-10 seconds
  • Be able to move around while super speed is active

From the research that I did I found information on ion wind propulsion but it does not seem that viable as a method for accelerating in atmosphere.

Pros: Ion winds can be generated using electricity which this character can control and can be hidden easily.

According to Wikipedia in atmosphere ion wind propulsion does exist however it only works in low orbits with relatively low thrust.

So in summary how could a speedster accelerate to Mach 5 without using engines, and alien tech?

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    $\begingroup$ how about magnetic propulsion through a railgun system? all that's needed is a magnetically sensitive bodysuit! a slight con might be that they won't be a humanoid on impact =^w^= $\endgroup$
    – alkahest
    Feb 24 at 5:47
  • $\begingroup$ If they were using a rail cannon how could they maneuver around? $\endgroup$ Feb 24 at 5:51
  • $\begingroup$ @Coolcats112 that's not part of the question criteria, so technically my joke still stands $\endgroup$
    – alkahest
    Feb 24 at 5:55
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    $\begingroup$ What do you mean by without engine? I can easily come up with over 9000 means to accelerate your speedster on your own terms but I just want to make sure we're on the same page that's why I need you to be more specific about your question. $\endgroup$
    – user6760
    Feb 24 at 7:02
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    $\begingroup$ "How could a speedster function in real life." no, that's why they only exist in fiction. The Flash even has a whole handwavium magic (the "speedforce") to justify the existence of the lead character. $\endgroup$
    – VLAZ
    Feb 24 at 9:54

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They can't.

There are many problems with this but the simplest is energetic. An object in motion has a kinetic energy equal to one-half its mass times its velocity squared. Mach 5 is about 1700 m/s, let's say your speedster masses a hundred kilos, that puts their kinetic energy at (.5 * 100 * 1700 * 1700) = 144.5 MJ.

The energy in your body is stored primarily in a molecule called ATP; at any given time, a human contains a couple of kilograms of the stuff. (About 0.1 mol or ~50g per liter.) A kilogram of ATP, when processed by the body, releases on the order of 60 kJ of energy.

If all of the metabolic energy available to a human body were released instantaneously, it would equal about one-sixth of one percent of the minimum required to accelerate it to Mach 5. (This is ignoring the inherent inefficiency of the acceleration method, as well as things like air resistance, waste heat, or what happens to the body now that it's burned off all its energy reserves.) There's room for improvement in the metabolism for sure, but not by that much.

Supersonic speeds just demand too much energy to be plausible through biological means alone. They require technological, if not super-technological means to supply energy.

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Accelerating a human body of mass 100 kg to Mach 5 in 1 to 10 seconds requires applying a force on it between 17 and 170 kN, or between 17 and 170 times its own weight.

No human body can resist those forces: tendons and ligaments snap and bones break, retinae detach and so on, already at lower forces. Maybe in certain configurations the lower end of that range can be accessible, but not repeatedly.

There is a reason why manned rockets have to go easy on the acceleration.

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  • $\begingroup$ For perspective, 25kN is a common rating on climbing carbineers. $\endgroup$
    – Cort Ammon
    Feb 26 at 1:38
  • $\begingroup$ Also, 275kN is the thrust generated by a Pratt & Whitney PW4062. Four of those jet engines power a 747 as it flies through the skies. $\endgroup$
    – Cort Ammon
    Feb 26 at 1:54

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