If a constant-charge parallel-plate capacitor is totally immersed in
water, the force of attraction between the plates is 80 times weaker
than the force of attraction in vacuum. However, if we thrust some
solid dielectric between the plates (not necessarily occupying the
whole distance between them - it could be rather thin), the force of
attraction becomes even greater than in vacuum. Accordingly, the
following four-step cycle (carried out very slowly) violates the
second law of thermodynamics:

1. Plates are immersed and fixed. We thrust the solid dielectric.
2. Plates get closer. We GAIN work.
3. We withdraw the solid dielectric.
4. Plates get apart; initial state restored. We SPEND work.

When the plates are immersed in a liquid dielectric (water), some
additional pressure between them emerges, pushes them apart and so
counteracts their electrostatic attraction (W. Panofsky, M. Phillips,
Classical Electricity and Magnetism, Addison-Wesley, Reading,
Massachusetts (1962), pp. 111-116). If the plates are vertical and
only partially immersed, the same pressure forces the liquid between
the plates to rise above the surface of the water pool (see fig. 6-7
on p. 112 in Panofsky's book). What if one punches a small hole in one
of the plates, just above the surface of the pool? Will the lifted
water leak through the hole and fall? If lifting is due to an
additional pressure generated within the bulk, as assumed by Panofsky
and Phillips, then water WILL leak through the hole and the second law
will be violated. No matter how weak the waterfall is, theoretically
it can rotate a waterwheel…

The perpetuum mobile of the second kind described above (as well as
the one described below) will never become a money-spinner and will
not solve the energy problems of humankind. However Nature may
occasionally have used such (inefficient from an anthropocentric point
of view) mecanisms and the knowledge of them could make us
unexpectedly rich in some unconventional sense.

Pentcho Valev wrote:

Take a suspended and stretched spring. It can lift a weight as it
contracts, that is, we GAIN work. However, in order to restore the
initial stretched state of the spring, we must SPEND work so there is
no net gain. If both contraction and stretching are carried out in a
reversible fashion, the net work gained at the end of the cycle is
zero.

Consider again a suspended and stretched spring but this time it is
"chemical", that is, we have one of the macroscopic contractile
polymers described by Dan Urry in:

http://pubs.acs.org/doi/abs/10.1021/jp972167t
J. Phys. Chem. B, 1997, 101 (51), pp 11007 - 11028
Dan W. Urry, "Physical Chemistry of Biological Free Energy
Transduction As Demonstrated by Elastic Protein-Based Polymers"

If, before contraction, we add acid (H+) to the system, the force of
contraction and, respectively, the work gained as the polymer
reversibly contracts increase. Then, just before stretching, we remove
the added H+ from the system: the force of contraction and,
respectively, the work spent as we reversibly stretch the polymer
decrease. At the end of the cycle, THE NET WORK GAINED FROM
CONTRACTION AND STRETCHING IS POSITIVE.

So far things go against the second law of thermodynamics but the
complete account requires that the net work gained from adding H+ to
and removing H+ from the system be evaluated. If it is positive or
zero, the second law is definitively violated. If it is negative, the
second law is saved for the moment.

In the absence of the polymer, adding H+ to and removing the same
amount of H+ from the system, in a reversible fashion, would amount to
zero net work gained. The polymers designed by Urry, however, release H
+ as they contract, and absorb H+ as we stretch them. It is easy to
see (for people experienced in electrochemistry at least) that this
makes the net work gained from reversibly adding H+ to and then
removing the same amount of H+ from the system POSITIVE.

Conclusion: The reversible cycle:

1. The polymer is stretched. We add H+ to the system.
2. The polymers contracts and lifts a weight.
3. We remove the same amount of H+ from the system.
4. We stretch the polymer and restore the initial state of the
system.

violates the second law of thermodynamics.

Pentcho Valev