Nobody ever teaches me how physics works

[Peegee]

The other day I defined 'wind' to my brother as 'a change in air pressure in large scales', and it got me thinking that either I don't pay attention in school or school did not teach me the most simple things.

Here an example I can't explain:

When you have a collision where the momentum are opposing, the collision magnitude is additive.

For example 20 N·s -> <- 10 N·s = 30 N·s of momentum, assuming there's no loss of energy elsewhere.

In the example 20 N·s-> 10 N·s -> , the object behind the object in the front strikes the object in the front, but with momentum 10 N·s
Why does this happen? It's not sufficient to say that it is intuitive, and I was never taught why things happen. I was simply taught to apply trigonometry and algebra and solve for the equation.

Are there any questions about reality you have questions about? For example the reason I don't fall through the earth is because of electrostatic repulsion, or something like that (this explains why solid things do not pass through each other). WTF

PS what am I asking? is there a term for it?