A tuned mass damper may be formed using one or more rotary magnetic dampers (108) coupled to a pendulous mass (102). The tuned mass damper thus formed may be used to suppress the motion of a man-made structure. The mass (308) of the tuned mass damper may be adjusted by adjusting the magnitude of the pendulous mass. The natural frequency of the tuned mass damper may be tuned by adjusting the distance from the mass center of the pendulous mass to the pivot point of the pendulum. The motion being suppressed may be generated by environmental factors such as waves, earthquakes, or wind, for example.