Activities about relative size

Wildfires in Canada have been spreading dangerous smoke pollution throughout much of North America. What is a dangerous size of particles per cubic meter (PM)? How tiny is...

We needed more toilet paper at home but there wasn't any at the store. So, I ordered this online. When it came I was surprised. Read on ...

How big is one coronavirus? How big is a micron? How well do these masks protect against the virus? What can you observe about the size of particles...