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.
If enough sediment is eroded away in one place, it can begin to form erosional landforms. A bay at place where a river meets the sea is an excellent example of an erosional landform. The size, shape, and scope of a bay can vary drastically by the composition of the rocks and soil surrounding it.