An alien spacecraft flies past Earth on a tour of the universe. They spot some apparently intelligent creatures and decide to leave them a present. The artefact is effectively a perpetual motion machine. It is a closed, indestructible metallic box with an axle projecting from one side - the axle has a rough surface. In theory it could have a wheel attached to it. It rotates at a constant rate of about one revolution per second and is pretty much unstoppable.
Unfortunately humans have not yet invented the wheel. A band of hunters find the cube shaped device which weighs the same as two men.
In this society - reliant on wood, hide, bone and stone tools - is there any use that they can find for the artefact or have the aliens wasted their time and a perfectly good artefact?