Consider the following idea: A ship heats its boilers and propels itself without the use of coal or oil in the following way. it pumps in warm sea water; extracts heat from that sea water; concentrates the extracted heat in its boilers; and discharges the cold water back into the ocean. The extracted heat in the boilers is then used to do work and propel the ship as usual. Does this violate a law of thermodynamics?

A) Yes, the 0th law.

B) Yes, the 1st law.

C) Yes, the 2nd law.

D) Yes, the 3rd law.

E) No.

Solution: C. The sea water cannot spontaneously heat the boiler if the boiler is at a higher temperature than the sea water. This would violate the second law of thermodynamics regarding the direction of heat flow. One could use a heat pump to force the heat to flow from a lower to higher temperature system, but the energy required to run the heat pump would meet or exceed the work done by the boiler, so it would make no sense to do so.

It does not violate the first law because energy could be conserved in such a series of processes. The zeroth and third laws don't have anything to do with this problem.