InventorsToolbox: The Elements of Machines. Simple Machines: These devices were all in common use for centuries before Leonardo's time.
Each one makes work easier to do by providing some trade-off between the force applied and the distance over which the force is applied. Wheel and Axle In this machine a wheel or spoke is locked to a central axle so that when one is turned the other must turn. For YOUR KIDS! Simple Machines Activities. Dirtmeister: Simple Machines.
"inQuiry Almanack" - Spotlighting... - March, 1997. Simple Machines Made Simple.