Can you make the ball bearings sit at opposite ends of the puzzle?
Leonardo Da Vinci conceptualised the first helicopter. He knew that the propeller on his helicopter design would need to rotate extremely fast for lift off, and that he would have to find a solution to the friction problem. Ball bearings, together with a lubricant, would significantly reduce friction, greatly increasing the propeller’s speed. Although the use of ball bearings was known to the Romans, it is Leonardo Da Vinci who is generally credited with their invention.