Turbulent flows are ubiquitous. They are central to natural processes from the depths of the oceans to the heights of our atmosphere, and beyond. And yet, turbulence remains one of the great unresolved problems in classical physics. But what does this statement really mean?
In the first half of this lecture we will understand some bits of what it is that remains unsolved. We will then discuss the effect of flows, often turbulent, on small particles - such as tiny organisms, pollen grains, or rain drops - which shape much of the natural world around us.