From an hourglass to the sand dune on a beach , we get laid that sand flows downhill . It ’s just what granular materials do . However , researchers have just discovered that it is potential to make a granular cloth that neglect this basic rule : A sand - similar substance that flow uphill and climbs stairs and walls .
The discovery was serendipitous . Lead source Dr Samuel Wilson - Whitford go steady the peculiar movements when he rotated a magnet beneath a phial of polymer particles coated in iron oxide . Without the attractor they moved like any sand - same mass medium , deport as the gritty flow equality would expect . But the magnetized subject field switch over things around .
" After using equations that describe the flow of granular material , " co - author Professor James Gilchrist , from Lehigh University , suppose in astatement . " We were capable to conclusively show that these particles were indeed move like a granular stuff , except they were flowing uphill . "
The material flowing uphillImage Credit: Laboratory for Particle Mixing and Self-Organization, Lehigh University
To explain the motion , the team had to make some unparalleled changes to the granulose flow equations . The angle of repose , the steep angle of descent that can be created in the material without it slumping , had to be negative . The friction coefficient also had to be negative .
" Up until now , no one would have used these terms , " Gilchrist add together . " They did n’t survive . But to understand how these grains are flow rising , we calculated what the stress are that cause them to move in that direction . If you have a negatively charged angle of repose , then you must have cohesion to give a minus coefficient of friction . These granular flow equations were never derived to believe these thing , but after calculating it , what came out is an seeming coefficient of friction that is electronegative . "
The charismatic arena is the cause of the counterintuitive movement of these so - called microrollers . It creates a torque so the particles pop out rotating , and it produces cohesion so the speck stick together for a little second . A stronger magnetic field increases the coherency , grant them more adhesive friction so they can go uphill even quicker . That ’s how they made them go up tiny staircases .
" This first theme just focuses on how the fabric course acclivitous , but our next several papers will calculate at applications , and part of that exploration is answering the question , can these microrollers climb obstacles ? And the answer is yes , " Gilchrist tell .
" We ’re studying these particles to death , " he say , " experiment with dissimilar gyration pace , and different amount of magnetized strength to better empathize their collective motility . I basically know the titles of the next 14 papers we ’re give way to print . "
The work is publish in the journalNature Communications .
