0:00:08.370,0:00:10.100
Looks a bit[br]like the Dance of the

0:00:10.100,0:00:11.440
Sugar Plum Fairies,

0:00:11.440,0:00:12.830
if they were made[br]of water

0:00:12.830,0:00:14.410
and propylene glycol.

0:00:16.040,0:00:17.080
That's the key.

0:00:17.080,0:00:20.060
Each droplet is composed[br]of two fluids.

0:00:20.060,0:00:21.570
The coloring is just[br]to help you

0:00:21.570,0:00:22.840
see what's going on.

0:00:22.840,0:00:24.490
The different fluids[br]evaporate

0:00:24.490,0:00:25.790
at different rates,[br]and they

0:00:25.790,0:00:27.730
have different surface[br]tension.

0:00:27.730,0:00:30.100
And the result,[br]in each droplet,

0:00:30.100,0:00:32.770
is kind of a constant[br]internal tornado.

0:00:33.960,0:00:35.610
Scientists at Stanford[br]found that if

0:00:35.610,0:00:38.310
that internal tornado[br]is disrupted,

0:00:38.310,0:00:40.960
then the droplets[br]chase each other around,

0:00:40.960,0:00:43.070
or form a line,

0:00:43.070,0:00:45.110
or even climb vertically.

0:00:46.670,0:00:49.060
And the reason[br]is that just a hint of

0:00:49.060,0:00:51.060
evaporation from one drop

0:00:51.060,0:00:53.110
changes the relative[br]humidity

0:00:53.110,0:00:54.790
near the surface[br]of the other drop.

0:00:56.630,0:00:58.370
The change in humidity[br]affects how the

0:00:58.370,0:01:00.220
water evaporates[br]from the other drop.

0:01:00.750,0:01:03.100
That changes[br]its internal tornado,

0:01:03.100,0:01:04.410
and the drop[br]starts to move.

0:01:05.640,0:01:08.010
The result is totally[br]fun to look at,

0:01:08.010,0:01:10.260
and it could be a[br]brilliant teaching tool.

0:01:11.020,0:01:12.610
Simple materials,

0:01:12.610,0:01:14.010
complicated physics.