Returning from Space

Abstract

Walking along the shore of a tranquil lake on a sunny, spring day,most of us have indulged in one of life’s simplest pleasures:skipping stones. When the wind is calm, the mirror-like surfaceof the water practically begs us to try our skill. Searching through pebbleson the sandy bank, we find the perfect skipping rock: round and flat andjust big enough for a good grip. We take careful aim, because we want thestone to strike the water’s surface at the precise angle and speed that willallow its wide, flat bottom to take the full force of impact, causing it to skip.If we have great skill (and a good bit of luck), it may skip three or fourtimes before finally losing its momentum and plunging beneath the water.Weknow from experience that, if the rock is not flat enough or its angle ofimpact is too steep, it’ll make only a noisy splash rather than a quiet andgraceful skip.