Apologies for the bouncy video... it's hard to hold a phone still, pointed backwards, while riding!
Ronan and I often get around via bicycle, with me pedaling and him riding in a trailer. When in the trailer Ronan likes to watch for large trucks, play with his model cars, read board books, and, on occasion, make his pinwheel spin. It's the pinwheel spinning that is most endearing- he puts it up into the wind and firmly holds it there, usually until it spins so fast that it gets stuck. Sometimes he watches it spin, but mostly he just holds it fast and gets back to searching for interesting vehicles on the road.
He seems to understand that it's the relative wind-speed that makes the pinwheel spin, as evidenced by his command for, "faster" when we are riding. Soon we'll discuss how to get the ideal angle of attack to optimize rotational speed.