SMALL CHILD: "So Mr. Richard, you talked about a screw machine? Why is it called a screw machine? Does it makes screws and stuff?"
BRIAN: "No, it's actually an enormous rubber dildo on the end of a mechanical device, powered by a 300hp industrial motor. The woman bends over and straps in here, and presses this button here... and the rotary motion of the motor denoted by the letter A is turned into a reciprocating thrusting motion by the mechanical arrangement here. By pulling the lever marked with the letter X you increase and decrease the gear ratio in the gearbox marked Z. Various combination of rotational power and gear ratio result in different mechanical motions as explained by Muzors and Gorham's third electromechanical thesis, section two.
SMALL CHILD: Fascinating, but what if we adjusted the position of the mechanical pivot on this part here, moving it here?
BRIAN: Ah, intriguing. *does math on chalkboard*