| MadSci Network: Physics |
Yes, a pendulum would swing forever if there were no non-conservative forces acting to slow the pendulum. No, it wouldn't be appropriate to think of it as perpetual motion in the same sense there are perpetual energy devices. Energy was applied to start the pendulum swinging and the only reason a pendulum might continue to swing forever is the energy in the system is never reduced. [note added by MadSci Admin: In reality there would be some (possibly very small) friction in the pendulum's mount or heat losses if the pendulum has a flex mount. In either case, a real pendulum will not swing forever.]
Try the links in the MadSci Library for more information on Physics.