In 1961 the world was bubbling with technological advancements.
The spring of that year President John F. Kennedy gave the country the goal of sending an American to the Moon before the end of the decade. Project Mercury was already underway, halfway to its mission of putting a human in orbit around the Earth by February, 1962. Only a few years earlier the Laser had been invented, and by the end of 1962 light emitting diodes would be developed at GE. In addition to the new frontier of space, visionaries such as Jacques Cousteau were working on permanent undersea living facilities. Science and technology were omnipresent and unavoidable.
Evidently DC editor Julius Schwartz and Flash writer John Broome figured that science also sold comics, shown by the "Flash Facts" pages, and the integration of basic scientific facts throughout the stories of the early 60's. A couple years later I'd pore over that information as if it contained the secret footnotes to Einstein's theory of relativity. Re-reading them as an adult, however, some of those facts break down, but they're still interesting.
The first half of Flash #121 is the story "The Trickster Strikes Back!"
Centrifugal Force - On one page The Flash performs several acts of super-speed. In the first frame the editor's note says "Flash's astounding speed enables him at times to defy gravity itself!"
parkour stunts, but how would it be possible for the Flash to run up the side of a skyscraper? Whenever Jackie does it he's using his forward momentum to hold him to the wall long enough to push off with his feet. Unless he's bouncing between two wall, the forward momentum can only last a fraction of a second.
My first thought was "centrifugal force," which would have been wrong. Wikipedia tells me centrifugal force is a fictitious force, created by a centripetal force combined with Newton's First Law: a body in motion tends to stay in motion. When the two forces act on the body it causes it to move in a curve, such as a ball on the end of string going in a circle. When the centripetal force is removed by releasing the string, the ball travels in a straight line.
So, for the Flash to move up a skyscraper he would have to either have had a massive centripetal force applied to him at the base of the skyscraper, or he would have a continuous centripetal force applied to him perpendicular to the building. For the sake of the story I'm imagining he grabbed a horizontal bar at the bottom of the building and swung around that. His speed was great enough to provide the force to fling the scarlet speedster along the path of the building in such a way that he appeared to run up the side.
Gyroscopic Forces & Electrical Circuits - In the third panel of the same page Flash performs a literal high-wire act. "By moving fast I can keep my balance! And the voltage in these power lines won't affect me as long as no part of my body is in contact with the ground."
The second half of the statement is easier to corroborate. In an electrical circuit a ground is used for a return path for the electric current. Since the wires may not be insulated, and also since electricity follows the path of least resistance, if Barry Allen touched both the electrical wires and the ground he would become a literal flash.
It's the first portion about "moving fast" to keep his balance that I question. No matter how quickly the Flash is moving, his inertia (see Newton's First Law above) will make him tend to move in the same direction. If he stumbles he'll stumble quickly and lose his balance. The Flash might want to take a page from the tech of one of the Rogues, the Top. If the Flash was spinning he could use gyroscopic force to maintain his balance.
Aerodynamics - In the final panel the Flash avoids ending up as a street pancake with one of his favorite tricks: "By thrashing my legs at super-speed...I build up enough air pressure under me to ease my descent...and hit the ground slow enough to avoid these wires."
Potentially this could work, like a bumblebee in flight, as long as the Flash had airfoils on his feet. If he had some curved surface or articulated plane that could catch the air and produce an aerodynamic force then it just might work. Unfortunately, despite the little wings on his boots, I have never seen anyone mention that the scarlet speedster's costume is aerodynamic. It's more likely he'd beat the air and suffer some shattered tibia before the stunt was over.
In Flash #109 the writer explains how the Flash can penetrate walls "just as a tornado-driven straw can penetrate several feet of solid oak." Evidently that was regretted because they have a new surprise for us: The Flash evades an explosion by vibrating through a wall, perhaps the first time he uses this soon-to-be-common technique. "By vibrating his body at hyper-speed the amazing Flash can penetrate a solid wall because the molecules of his body in super-vibration slide past the molecules of the wall!"
Ok, believe it or not, we already have an example of molecules moving through walls: it's called osmosis. In osmosis water and other liquids move through a semipermeable cell wall without disrupting the membrane. Since humans are mostly water, it's just a short logical step from osmosis to the Flash vibrating through a wall, right?
Luckily, the Flash is able to overcome all these scientific hardships and put the Trickster behind bars once again.
In the second story, "Secret of the Stolen Blueprint!" Barry Allen attends his 10-year college reunion and meets up with a classmate who's working on a new hydrogen power generator. Spies steal the device and the classmate, who knows Barry's a friend of the Flash, asks for the superhero's help.
Persistence of Vision - In order to make it appear that Barry Allen and the Flash are two separate people, the Flash performs a stunt moving at great speed so it seems that both Barry and the Flash are in the room together. As the editor notes, "scientifically this effect is the same as that seen on a motion picture screen where the frames succeed each other so swiftly that they give the appearance of continuous action! By super-speed, Flash is enabled to appear in place as Barry or himself a sufficient number of times per second to fool the eye into thinking he is there all the time!!"
What the writer fails to mention is that in a motion picture camera there is a shutter that interrupts the image between frames, causing us to see a series of individual frames rather than a blur. Using persistence of vision, our brains merge the stream of individual frames into moving images. If it weren't for the shutter movies would be a muddled affair.
In the Flash's case, he would have to have some way of darkening the entire room in the transition times between Barry Allen and the Flash. Otherwise, his college chum will see a red blur passing between the images of the two men.
Turbulence - The Flash tracks the hydrogen power plant thieves to a submarine, and dives into the ocean. The editor makes two comments on this page. "At super-speed, the World's Fastest Human can swim for miles under the surface without rising at all!" and "Just as a powerful ship in passing can pull unwary swimmers into its propeller wake, so Flash can create the same effect!"
As far as being able to swim for miles... the average person can hold his breath about two minutes. In various issues of the comic the Flash has run around the world in less than a few seconds. We know from the Flash #108 he can surpass the speed of light. In that case it should be easy to swim for miles in less than two minutes, but the big question is how the Flash can expend so much energy using only the Oxygen available to his limited capacity lungs?
Thanks to the DC Comics Database for a memory refresher on the plots of Flash #121.