Friction
Friction is an interactive sim. It changes as you play with it. It has a Play Area and a Control Area.
Chemistry book rests lightly on top of a Physics book, and is ready to be rubbed against it. In zoomed-in view of where books meet, surface temperature is cool, and atoms jiggle a tiny bit.
Grab Chemistry book to play.
If needed, check out keyboard shortcuts under Sim Resources.
Play Area
Look for grab buttons. Once grabbed, use keyboard shortcuts to move book or zoomed-in book.