What is friction?

Ever wonder why it's so hard to get a heavy box movin', but easier once it's already slidin'? Check out this stationary object; it's stuck because the force you're pushin' with is being perfectly matched by friction's resistance. At a microscopic level, you've got these asperities, which are tiny, jagged ridges on both surfaces that interlock like mountain ranges keepin' everything jammed in place. This grip is even tighter because of the normal force, the weight pressin' down that squishes those ridges together. Now, look at the sliding object; once you break that initial grip, the surfaces start glidin' over the peaks of those ridges. Instead of just jagged teeth, we're now dealin' with molecular bonds constantly breakin' and reformin' as the surfaces zip past each other. All that microscopic smashin' and bond-breakin' converts kinetic energy into thermal energy, which is why things feel hot when you rub 'em together! Tiny Concepts.