According to the commonly held theory of Physics, entropy cannot decrease in an isolated system. In the framework of a theoretical study, the performance of work in isolated systems, at the expense of some thermal energy, which disappears, is shown to be conceivable instead of impossible. This occurs through the Brownian motion of a nanoresonator. A decrease in the thermal energy of these particular systems, that is, a fall in temperature involves a decrease in their entropy. The main finding is that a mechanical resonance is able to directly convert heat into work. Experimental devices are described