Heat will loosen a nut on a s***w. How, scientifically, does this work?

Question

Little brother's school project.

Answer 1

the whole nut expands, because of the heat. This includes the hole in the nut, so the becomes looser.

Answer 2

Heat makes metal expand, simply heating a bolt won't work.  Look at the tip below.

d**k Williams: I just want to pass on something that works for me when removing very stubborn bolts. Heat the bolt with a torch - a propane torch will work on small bolts. Once the bolt is hot - just starting to glow red in really stubborn situations - then touch the threads with paraffin wax, with the bolt situated so that the wax runs down into the mating threads. Then remove the bolt. I used to use this method to remove drain plugs from engine blocks. It always worked. I've also used this to remove small phillips head screws that were corroded into pot-metal tail light housings.