Low- circuits are therefore damped and lossy and high- circuits are underdamped. While wind resistance is higher, wind-induced oscillation can be damped at bundle spacers. The system must also be damped to avoid oscillation. Driven harmonic oscillators are damped oscillators further affected by an externally applied force "F"("t"). Boeing designed a hydraulically damped toilet seat cover hinge that closes slowly. The equilibrium is stable if small perturbations are damped and unstable if they are amplified. These used a lever arm which moved hydraulically damped vanes inside the unit. The engine is prone to vibration, which is damped by large rubber engine mounts. Since they are not damped, they are highly efficient, but they also produce strong resonances. This represents a damped simple harmonic motion. On the smaller scale, perturbations are damped almost instantaneously. This is called the damped resonance frequency or the damped natural frequency. The solution of a viscously damped system is somewhat more complicated. Rear wobble is heavily damped and falls off quickly as bike speed increases. The "Q" factor determines the qualitative behavior of simple damped oscillators.