College Physics with MasteringPhysics 7th Edition by Jerry Wilson,Anthony Buffa,Bo Lou

Exercise 115

An inventor comes up with an idea for a perpetual motion machine, as illustrated in Fig. It contains a sealed chamber with mercury (Hg) in one half and water (H 2 O) in the other. A cylinder is mounted in the center and is free to rotate. Tire inventor reasons that since mercury is much denser than water (13.6 g/cm 3 to 1.00 g/cm 3 ), the weight of the mercury displaced by half the cylinder is much greater than the water displaced by the other half.
Therefore, the buoyant force on the mercury side is greater than that on the water side-more than thirteen times greater. The difference in forces and torques should cause the cylinder to rotate-perpetually. Would you invest any money in this invention Why or why not

FIGURE Perpetual motion See Conceptual Question.