If you only knew how complicated even the simplest things were lol... The main thing I learned in engineering is everything is complicated. I interned at BorgWarner for a while last year (til the car industry in America collapsed) and they are the world leader in automotive parts and engine testing, they invented automatic transmissions, silent chains, VCT etc. Anyway. They're really famous for accoustics. You know that clunk your door makes when you close it? Do you know how much testing went into it? The clunk your door makes was engineered to sound exactly like it does through testing, surveying people on ear-pleasing clunk sounds, etc. The shape of a shift knob is another example. The way I got the underlyign frequency was a combination of my differential equations class (Fourier series and resonances) and testing at BorgWarner that I can't really describe but basically they found that if certain parts of the car vibrate at specific frequencies it can hinder/help other parts, so each part is designed to harmonize with the other parts. This is what lead to silent chain, amongst other things. EVERYTHING is complicated when you get down to the molecular level.