Band Around the Earth 
Copyright ©1997 by Paul Niquette. All rights reserved.
IWorld Globemagine a band snug around the earth. Add 10 feet to the band. It is no longer snug. There is now a gap uniformly distributed around the earth. 
The gap is just large enough...
{a} to walk under, 
{b} to crawl under,
{c} to slip a razor blade under, or
{d} to allow a virus to swim under.