Your 8 year old's play date was spent making something to take things from the second floor down without damage. That part is probably not that unusual for boys but here's where it was a bit unique - they spent a LONG time drawing up designs (various gliders and parachute designs) and even more writing a lot of equations to figure out which of their designs to go with. The equations are pretty funny, I don't recall there being a constant for air resistance but according to DS and his friend AR=56.

As the kid left he was yelling "and next time we're going to do tonnes and tonnes of amazing math". Love that my oddball has found a kindred spirit.