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.
Erosional landforms such as river valleys and coastal cliffs are formed when forces such as wind and water wear away surfaces. Erosion often takes a significant amount of time, but its effects are easily measured by examining geological evidence such as rock layers.