The random motion of small particles in the air is called Brownian motion (named after the botanist Robert Brown). This motion is caused by the collisions of the particles with the molecules of the...
Molecules in a fluid move constantly, freely, randomly, in all directions and with all possible velocities. This erratic motion of the molecules causes them to collide with anything in their path....
Dust particles move around because of the air around it. Even though the dust particles aren't alive, they can still move because of the air around them and us!!!!!