Basically, a passive radiator is a reactionary device as the name suggests. When a driver (such as a subwoofer) is mounted to a sealed speaker box (enclosure), the physical forward/back movement of the speaker affects the internal air pressure of the enclosure.
Three landforms created by wind are; sand dunes, yardangs (half-teardrop shaped formations hill sized, and deflation hollows (wind swept depressions.
The scraping and plucking of glacial erosion creates a number of distinct landforms and features. If the glacier erodes into a mountain, it can create a cirque, which is a round hollow with steep sides. It's as if the glacier scoops out the side of the mountain like an ice cream scooper.