"Friction is a very good thing," remarked a passenger.
There is a beautiful tale of Scandinavian mythology.

A hero, under the promise of becoming a demi-god, is bidden in the celestial halls to perform three test-acts of prowess.

He is to drain the drinking-horn of Thor.

Then he must run a race with a courser so fleet that he fairly spurns the ground under his flying footsteps.

Then he must wrestle with a toothless old woman, whose sinewy hands, as wiry as eagle claws in the grapple, make his very flesh to quiver.