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.
large, rounded landforms developed in massive rocks such as granite by exfoliation. These are formed as a result of pressure release and sheeting where layers of rocks have peeled awaay leaving behind rounded rock surfaces. can be up to 15m thick. e.g. Stone Mountain in Georgia and Half Dome in Yosemite.