Gerhard Fiedler wrote:
> Not necessarily. It could be that the energy would get transformed from
> kinetic energy into other forms (heat?) anyway -- float or no float.
> Maybe the float just redirects a small part of the energy flow that
> goes from kinetic to thermal into electric instead; in that case, the
> float wouldn't introduce an additional slowing, but would cause a
> certain ever so slight cooling.

My point was where the energy was coming from in the first place.  I say it
comes from the kinetic energy stored in the rotation of the planet.  You
seemed to disagree so I wanted to hear where you think it does come from.

But to address your comment above, you are saying that the energy in moving
the water up and down as tides gets dissipated anyway, therefore directing
it to make electricity doesn't remove any additional energy from the source.
I disagree with this also.  My main argument is that much of the energy is
not dissipated, but returns to the system.  It's sortof like bouncing a mass
at the end of a spring.  Once you get it going, it take relatively little
power to sustain a large oscillation.  That's because little is being
dissipated.  The energy just gets sloshed around between the spring and the
mass.  Only the little bit lost to friction and air resistance must be
replaced by the driving mechanism each cycle.

Certainly there is energy dissipated by the oceans as they rise and fall due
to tides, but most of it is stored and released as potential energy in the
height of the water column.  Think of a planet that has a uniformly thick
ocean layer over a perfectly smooth solid core.  The tides would be
traveling waves.  They would loose a little energy in the internal friction
of the water due to viscocity, and some more in the friction with the
ground, but most of the energy would be transferred around the globe in a
big wave.  The driving force is essentially in phase with the motion.

Now think of a large float used to extract this energy into up/down motion
of a fixed mechanical system.  If there is no force on the mechanical system
(the float just bobs in the water), then no energy is extraced.  To extract
energy, there has to be a force in the direction of motion.  This means the
float must be lagging the wave, causing a phase shift in the wave itself.
Once the wave is lagging its driving force, the driving force must be
imparting more energy to the wave.  The extra energy has to come from
somewhere, which is the kinetic energy stored in the earth's rotation long
ago.


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