To most of us, wheels seem pretty intuitive. You’ve probably known from an early age, for example, that circular or rounded things roll more easily than boxy or angular things. Knowing this, it’s hard ...

Way, way back, when your caveman grandpa or grandma had to lug something heavy back to the cave, what did they do? Maybe they carried it. Or dragged it. Or tumbled it down a hill. But what they didn't ...