There are two thing that have never made sense to me when it comes to Flash.
NUmber one, how can he be FASTER than a guy like, say, Superman, Superman can move at lightspeed and nothing can move faster than light.
Tachyon particles are merely hypothetical and most Physicists don't actually believe in particles that are faster than light..
Number 2, how can he throw infinite mass punches? He is still mortal beside his speed right? If he throws a punch that sends his arm hurtling at the speed of light, the tremendous impact may not effect his arm (which is traveling at a very high speed) but his arm is connected to his shoulder, torso and entire body which is not traveling at the speed of light. That impact would wreck the rest of his body.
Now he could possibly charge at something using his entire body with his fist extended, but then he would have to go back and do the same thing over again to land another punch (wheras a guy like Superman can throw multiple punches from a single position because there is a rational explanation for how his body can take the impact.
1.) Flash is faster than Superman and can quite easily travel at lightspeed and beyond. Pretty much any thing you or I or anyone else knows about science or physics means nothing to the Speed Force (or really comics in general, in my experience, but especially the Speed Force).
2.) The "Infinite Mass Punch" is something of a misnomer, imo. I don't think he's literally hitting people with infinite mass, but rather hitting them with some absurd levels of mass as he approaches "infinity" speed wise, if that makes sense (it really doesn't in scientific terms, but bear with me on this). The Speed Force also prevents nasty side effects of doing things at super speed such as shattering bones and ripping muscles if you're a normal human. Basically, it lets Flash hit things at superspeed with no more of a recoil than if someone where to punch something at a normal speed. That said, he can bust his knuckles if he strikes something hard and fast enough.
Superman was putting up mental blocks, the Flash was using his infinite strength and momentum against him because has more control at great speeds.
__________________ "Compounding these trickster aspects, the Joker ethos is verbally explicated as such by his psychiatrist, who describes his madness as "super-sanity." Where "sanity" previously suggested acquiescence with cultural codes, the addition of "super" implies that this common "sanity" has been replaced by a superior form, in which perception and processing are completely ungoverned and unconstrained"