Compressed air and diesels
I had a hard time understanding how a diesel could work without sparkplugs, then I started fixing AC units. I soon learned how hot compressed gas can get when I touched the high pressured line of an AC unit and burned my fingers. Meanwhile, the low side stays icy cold.
It is the same force that causes Houston to be so hot in the summer when High pressure sits on top of us.
Compress air and it heats up.
Diesel train engines don’t drive the wheels; they drive a generator that creates electricity. This electricity drives motors attached to each wheel. I didn’t learn this until recently when I was reading a book about trains to my son. I was surprised.