Kelly Forbes, age 14, of Richmond, British Columbia, Canada, for his question: .

DOES PERPETUAL MOTION EXIST?

It has long been a dream to build a machine that would run forever with no energy input. But no one has ever succeeded in building such a machine, and almost all scientists and engineers believe no one ever will.

Two machines have been suggested: one that would run forever without receiving energy from the outside, and one that would run forever and produce work by taking energy from the sea or from the atmosphere. The first would have to run without resistance, and all moving parts in a machine are subject to friction and some kind of resistance. The second could run only if all the energy of the randomly moving molecules in the source could be completely converted into useful work, but no machine has been able to do this.