I did a experiment. I made a vacuum chamber with a silo on the top. Also provided the butter fly valve between vacuum chamber & silo. Filled the silo with low density powder say 0.2 gm / cc. Created vacuum in silo having powder and vacuum chamber. When I dropped this powder in vacuum chamber some powder did not travel straight down there was dust cloud. Why it did not travel straight as there was no air resistance. May any one has answer.