ScienceScience Now  Watch! Small objects levitate, dance on
sound waves you can't hear  Researchers in Japan are fighting
gravity with sound. In the video above, you can watch as a
series of small, lightweight objects float and dance in thin air
-- manipulated by invisible ultrasound waves.  The sound waves
are not just invisible, but also silent to our human ears. 
"The human ear can detect up to 20 kHz frequency, but we use 40
kHz transducers that are out of the range that humans can
detect," said Yoichi Ochiai, a PhD student at the University of
Tokyo who put the video together. "So we can't hear the sound
from our speakers."   But even if you can't hear the waves, or
see them, you can feel them. According to Ochiai, if you stuck
your hand in the middle of the glass-square where the objects
are manipulated, you would notice what feels like a wind
blowing.  Scientists have known that standing ultrasound waves
can cause an object to levitate since 1975, but the video above
shows that these waves can also be