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.
Erosion is the natural process where the earth and its soils are broken down by wind and water. As a result of this natural process, channels, gulleys, canyons and many other natural geological phenomena are created over hundreds or thousands of years.