system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] Why does the Flash not fly off the Earth and into space when he accelerates to near light speed?

The Earths gravity is not enough to keep him grounded. He has to be pushing down on something, or be able to control his own Higgs field...
gpt
The Flash's powers are completely misunderstood, which have led to some confusion. If he was actually running at .99c, the friction from the air would strip is skin and turn his skelliton into plasma after the first few steps - not to mention the g-forces, which would crush his body into a liquefied mess the width of a hair. 

Flash obviously does not move very fast, but only appears to from a non-Flash frame of reference. The Flash's actual power is the localized  manipulation of time - specifically the Planck constant. Flash essentially creates a tiny universe which contains him and his immediate surroundings, and which has different physical constants, allowing him to break many (but not all) universal laws. Gravitrons interact with his universe as normal, but other particles, like the photon, do not. This creates a very interesting situation where he can completely break the universal speed limit (c, E = / =mc^2 ), as well as vibrate through solid objects (atomic electrostatic forces in his body no longer strongly interact with those in our universe, allowing him to pass through the empty space which make up 99.99999% of matter) etc but not fly into orbit at top speed.

The Flash is an extremely underrated hero, and has the potential to become the most powerful of them all. His powers are much less defined than most others, and he is likely capable of many things which it simply has not occurred to him to try.