1. Dust particles move randomly in one direction / all directions. 2. The dust particles are supported by a fluid. The fluid is a gas / liquid.
3. You cannot see the gas / dust particles directly as they are too small, but they are there.
4. The gas particles move slowly / quickly in random directions.
5. The particles have many / few collisions which means they bump into each other.
6. Each time a gas particle hits a dust particle, it moves away in the same / a different direction.
7. Robert Brown first observed this with pollen / sugar particles in water. 8. In this case, the fluid was a gas / liquid.
9.The pollen grains appeared to jiggle randomly because they were colliding with water molecules / air particles.