Why escalator steps flatten out

0:00 Watch the bottom of an escalator and you will

0:03 see each step start out flat,

0:05 rise into a staircase,

0:07 then flatten again at the top.

0:09 That is not the step changing shape.

0:11 Every step is a small triangular platform on

0:15 two sets of wheels,

0:17 and the two sets ride on two separate tracks.

0:21 In the middle of the run the tracks sit at

0:23 different heights,

0:25 which tilts each platform into a stair.

0:27 Near the ends the tracks converge to the same

0:30 level,

0:31 so the platforms rotate back to flat and

0:34 slide neatly under the comb plate.

0:36 Nothing folds, nothing deforms.

0:39 The whole illusion comes from two rails

0:42 quietly drifting apart and back together.