Particulate matter sometimes blurs the air and reduces the visibility. However, apart from sandstorms and big fires the particles themselves are usually not visible, because they are by far smaller than 100 µm. Therefore we hardly notice the transport of particles in our environment.
Idea and approach
Flour can be used as a simple source of particles in order to demonstrate how they are carried through the air driven by wind and air streams. Dispersed flour powder generates particles which are sufficiently large in order to be seen but also sufficiently light in order not to sink immediately to the ground. We would like to observe how the dust is carried in the air.
1. Cutout from the setup with and without raised flour dust.
Material
table with rolls or high roll car (e.g. mobile laboratory table) tarpaulin black cardboard stones several barriers made from plastic or other washable material extension cable multiplug connector hair dryer a few tablespoons of flour
2. The tools: tarpaulin, flour and hair dryer
Preparation
The rolling car is moved to the schoolyard. Dry weather and moderate wind might be ideal conditions for the experiment. We spread out the tarpaulin over the table and install a few barriers (10 - 50 cm height). The barriers may be put on the tarpaulin or be hidden under it. We put three discs from the black cardboard (diameter about 30 cm) on the ground and pin it down with a stone. We put the plug of the hair dryer into the multiplug connector (extension cable). About one tablespoonful of flour is put on the tarpaulin, so that it can be blown in the wind direction over the barriers.
Experiment
We orientate the air stream of the hair dryer in wind direction and bring it slowly closer to the flour, until the powder starts to be dispersed in the air. We observe the dispersion before and behind the barriers. We can see on the black cardboard on the ground, how far detectable amounts of flour are carried through the air. But we need to consider that particles are also formed and transported which are too fine to be seen or detected.
