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
Double tap and hold to drag Chemistry book. Lift finger to release.