According to common knowledge, superheroes are physically impossible. And, for the most part, common knowledge is correct. We can't have superheroes in the real world, because that would be terrible and dumb and also completely impossible. Fine. We all accept that, and we promise to grow up now and start doing our taxes.
... Are all the grumpy old people gone now? Good. Superheroes are totally real, you guys! Or, at least, some scientists have come up with some pretty neat explanations for how their powers would work, if they were real. Which is not at all the same thing as the thing I just said but it's close enough for me because man is this stuff cool. So just suspend your disbelief for a bit and check out how ...
5We Know Why Superman Doesn't Kill People When He Catches Them
Not to state the obvious or nothin', but the logistics of Superman's super-strength have never stood up well to scrutiny. I mean, it explains how he can cause the deaths of millions of people through wanton carelessness like in Man of Steel, but what about when he "rescues" an innocent person falling to their death by giving them a supersonic mid-air spear tackle? Supes should've gone through this helicopter pilot like a finger through an over-soggy nacho.
There's also that time Kal-El (More like Kill-All eh? Eh? Yeah.) stopped an airplane by pushing on the nose -- why didn't he just puncture right through it, like a speargun through a baby dolphin's adorable, grinning face? Even if he matched the plane's speed, the entire weight of the plane is resting on a point the size of Superman's hand. No way that works. Well, it turns out that there's a scientific explanation for that, it's called "negative mass," and even though I may not totally get it (I'm very dumb) I think it's pretty freaking cool.
"Negative mass" is the theoretical physics version of "opposite day:" it's matter that behaves the exact opposite as how it should. Push it away from you, it flies toward you, and has negative weight -- which, though sounding pretty ridiculous, is actually mathematically sound, if hypothetical. You have to remember that there's still a lot we don't understand about the universe, and this hypothetical state of matter is how we explain some of those questions. Like why cooking shows are popular.
So the idea is that the sun (the source of Superman's power, remember) stimulates his ability to control negative matter the same way it stimulates our ability to get cancer. Then he spreads a web of that negative matter through the airplane, reducing the momentum without damaging the plane too much. And he could probably do the same to that helicopter pilot, right? Anyway, that's why Superman hasn't killed Falling Lois Lane 300 times over. I buy it, but you're welcome to explain what I'm missing in the comments.
4We Know How Captain America's Shield Works
In a movie-universe that prominently features red-skinned demon-men using space alien technology to fight World War 2, Captain America's Shield is the only part that, by my estimation, is actually physically impossible. I mean, check out this supercut of Cap's shield-throws:
Half those throws make no sense -- where did it go? Why did it decide to bounce there, but stick there? When it does bounce, why does it always come right back to Cap's hand -- does Captain America also have super-geometry skills? And if so, what? Turns out there's a surprisingly satisfying answer that, amazingly, doesn't even rely on totally bonkers theoretical properties of matter.
According to Howard Stark, the core property of "vibranimum" is that it's "100% vibration absorbant," which is why Agent Carter's bullets fall to the floor instead of ricocheting off them when she shoots Steve four times just for getting a little Natalie Dormer lip-action, holy shit. But that's insane, because that means the shield is just perpetually absorbing energy, which can't be true -- unless the shield is a battery. And that, my friends, explains the ricochet.
Okay so bear with me: if Cap throws his shield one way (say with the right wrist-flick?) then when it strikes an object, it releases some of the energy stored inside from the bullets/punches/crash-landings, shooting the shield off in the direction Cap intended. But if he throws it another way (counter-clockwise? I dunno) then it doesn't bounce -- it absorbs the vibration and buries itself in the wall. Which explains why he can embed his shield in a steel-plated wall in one scene, and then bounce it off the tail of a jet forty minutes later.
Maybe it also explains why it causes explosions?
And as for Cap's super-geometry, well ... maybe he's got a magnet of some kind, and the vibranium's release of energy also propels it back towards that for... some ... reason? Help me out, guys. We can do this. As a team.