My boss just walked into the room and asked “Why can you drink freshly poured coffee but if you spill it on yourself you end up calded?”. Now I sorta thought that, well, you can drink some but you couldn’t down it in one so it’s to do ith the heat energy being greater in the larger mass of coffee. But if you spill only a little on your hand it still smarts. Anyone?
As you sip coffee, you suck air across the surface of the coffee as you bring it into your mouth. This effectively cools the coffee so it doesn’t burn the inside of your mouth.
If you took a gulp of coffee, it’d be hotter.
Your mouth also deals on a regular basis with hot stuff: coffee, spaghetti, Pop-Tarts. Your mouth can therefore tolerate heat much better than, say, your crotch.