Question

why dust generally settles down in closed room???????

Answer 1

a small dust particals acquire a very small terminal velocity and remain suspended in air because of the small size . therefore they will settle down in a Closed room after some time

Answer 2

hey mate here is your answer...
yes, It happens like so because, one reason can gravity force also, because it will draw down all the dust particles towards the surface.
other reason can be that if a room is not open for a long period of time than basically a lot of dust particles will settle down in the room.
"hope, This will help you"...