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Science, Maths & Technology

The science of ceiling-walking

Updated Friday 2nd June 2006

Flies do it, spiders do it, even geckos do it – but humans are useless at walking on the ceiling. What do those creatures have that we don't?

Gaffer tape Copyrighted image Icon Copyright: BBC

The inventors of hook-and-eye fasteners met up with the humble blow fly for inspiration. These ceiling huggers wear two flaps of membrane on their feet called pulvilli - tiny hooked adhesive hairs - which allow them to cling to any surface. Velcro copied this design making fasteners like the blow fly wears on its feet. These then get "stuck" into the loop component of the fuzzy side.

Gecko's feet are even more high tech. The fine hairs covering their feet appear to use something called 'Van der Waals' forces - a weak attraction molecules have for each other when they are brought very, very close together.

The combined force from the gecko's half a million hairs on each foot - plus the fringe of 1,000 sub-microscopic hairs branching from each hair - have a powerful effect. The gecko's little feet have an adhesive force theoretically capable of holding 90 pounds or 40 kilos.

To move, the gecko releases each foot by peeling off the hairs, rather as one would adhesive tape. These forces are now being investigated by scientists who hope to use the same technology for upside down robots.

 

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