Is the earth a perpetual motion machine as it appears to rotate almost
at a constant rate indefinitely.  Where is the enormous energy coming
from to rotate the earth and how can we harness this rotational
energy?

Hello silverhill,
I know it is hard to believe, but the earth is slowing down and is not
a perpetual motion machine. This link does a real good job of
explaining the subject: http://pages.prodigy.com/suna/earth.htm

It is a known fact that the rotation of the Earth is gradually
slowing. For four and one half billion years, its entire life, it has
been slowing down. As the Earth loses its kinetic energy due to all
forms of friction acting on it (tides, galactic space dust, etc.) like
any other flywheel, it will slow down. From time to time our
timekeepers must adjust their super accurate atomic clocks to
synchronize them with the Earth's slowing rotation whose day/night
cycles we base our lives on.

Scientists estimate that the Earth's rotation is slowing at the rate
of 2.2 seconds every 100,000 years. The time it takes the Earth to
complete one rotation increases 2.2 seconds every 100,000 years. This
is a very conservative figure considering the number of adjustments
our timekeepers have been forced to make in recent years. If we trace
this phenomenon back in time, whatever the correct figure is, at one
point in time it may have taken the Earth 12 hours to complete one
rotation, (depending on its initial speed of rotation when it was
created.) At that time the Earth was spinning at twice the speed it is
traveling at the present time.

There is more that follows in case you are interested. Sorry to be the
one to ruin your plan for an unlimited energy source.

Redhoss

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Request for Answer Clarification by silverhill-ga on 06 Aug 2003 16:14 PDT

Thank You for your answer redhoss.
For all practical purposes i would think that the earth is the closest
to a
perpetual motion machine that you would get.  The slowing effect is
absolutely
minimal.  The energy inserted in order to achieve this spin or indeed
the spin
of any planet must be immense.  I wonder have any planets slowed to a
stop!
I would imagine that they're all merrily spinning even after the
passage of
billions of years.  So how much energy must be put into a system to
spin a
planet the size of the earth for 4 billion years?
You would also wonder how planets started spinning after their
constituent parts came together under the influence of gravity.
It's clear that the kinetic energy is immense and there must be some
method
of harnessing it, I would like to hear some ideas.

---

Clarification of Answer by redhoss-ga on 07 Aug 2003 12:09 PDT

Hello again silverhill,
     I am very sorry. I didn't intend to blow off your idea and
discourage your thought process. I am a mechanical engineer and had
several thermodynamics professors beat any ideas about perpetual
motion machines out of my tiny brain years ago. However, it is usually
the person who throws prior knowledge out the window and explores new
ideas who makes the greatest discoveries. Your ideas may be the
technology which saves the earth and mankind. I have no idea myself
how to harness the great kinetic energy stored in the slowly decaying
spinning of this planet. The only thing that I can say is that it
might be a very ineficient process and the results might be worse that
what we are doing now. I did run across some more information that you
might find interesting.

Here is a link to a discussion between several people about the exact
idea you propose:  http://speculativevision.com/forum/messages/262/1739.html

Here are some more ideas about "free energy" sources: 
http://speculativevision.com/forum/messages/262/1739.html

I don't know how math oriented you are, but I found this interesting:
http://216.239.57.104/search?q=cache:ATBBSP7B9yUJ:www.eas.purdue.edu/~calais/teaching/eas450/gravity.pdf+gravity+rotation+earth&hl=en&ie=UTF-8

I also ran across this interesting article:
http://www.novan.com/earth.htm

You asked where the energy comes from that causes the earth to rotate.
One theory is that the earth was formed from swirling gases that
became more dense as they rotated and the rotational speed became
faster as the gases formed into a more compact form. Just like an ice
skater spins faster as they pull their arms in toward their body.
Since this original spin was started there has been no more energy
added (one theory).
Hopefully you or someone with a questioning mind like yours will
indeed find the answer to an unlimited source of energy.

Keep looking, Redhoss

Silverhill asks how we can harness this immense energy. It is a good
question, and from what little I know, I assume if we were to harness
it, the result would be to accelerate the slowing down effect -
something we may be able to live with, at least better than global
warming from burning fossil fuels. How much energy would be gleaned by
harnessing a 1% increase in the length of the day, I wonder? And how
could we do it? Since tides are a slowing effect, I am guessing that
by harnessing tidal energy we would be increasing this slowing effect
- hence lengthening the day? We could also look at tapping the heat of
the molten core. This would cause part of the core to cool and
solidify, which would have the opposite effect on the earth's rotation
because the churning effect of a fluid core is itself slowing the
earth. That's enough rambling on from me. I'd be interested in other
readers' comments though.

It's worth pointing out that Earth doesn't require a continuous input
of energy to keep rotating; it has the property of inertia, and will
spin unabated until some interaction with another body exerts a torque
upon it, changing its rate of spin.

   But the planet does have an enormous rotational energy. This energy
is given by the relationship

E = Iw^2/2

E = energy
w = angular rate of spin, in radians per second (7.279 x 10^-5)
I = moment of inertia

   The moment of inertia for a solid sphere, such as planet Earth, is
given by

I = 2mr^2/5

m = mass (5.975 x 10^24 kg)
r = radius of sphere (6.371 x 10^6 m)

   This all yields a rotational energy for Earth of 2.57 x 10^29
joules. If (somehow?) we were able to rob the planet of one percent of
one percent of its angular energy, we'd harvest enough energy to meet
the world's current needs for over 76,000 years. As for how to
accomplish this, I haven't the slightest idea! :)

-Mark Martin

playtiagainsam has it right--tidal power does indeed harness the
energy of the earth's rotation. See:
http://www.iclei.org/EFACTS/TIDAL.HTM

The above page explains how the earth's rotation causes the
differences in water levels with respect to the earth's surface that
we experience as tides. If the earth were not rotating, tides would
change very slowly--only as fast as the moon revolves around the
earth, or the earth around the sun.

Of course, generating power from tidal flow increases the drag on the
water. The energy extracted from the tides has to come from somewhere,
after all! This means that extracting energy from tides would increase
the speed of the earth's rotation. Worried about "rotation pollution"?
The total world consumption of (nonbiological) energy in 1998 was 379
quadrillion btus, according to
http://energy.cr.usgs.gov/energy/stats_ctry/Stat1.html#WProduction

Assuming the value of 2.57+e29 (as calculated by Mark Martin) is
correct, you could extract energy from the earth's rotation for 643
million years before the earth's rotation would grind to a halt. At
that point, the length of a day would be one of our current years.
(This assumes energy consumption remains constant at 1998 rates, which
of course is not a good assumption. Still, I don't think we need to
worry about any of our activities slowing the earth appreciably, or
even measurably.

For links on tidal power see
http://power.about.com/cs/tidalpower/

--Mark Johnson

Another few comments. First, if the Earth is slowing down, where is
all that energy going? Turns out it's going into several places.
First, it's going into sloshing all that water around on the Earth
(the tides, as mentioned before). It's also going into flexing the
earth's crust, because the earth is not completely rigid. Yes--there
are tides in the ground as well as in the sea!

But there's an even stranger answer. Believe it or not, most of the
energy from the earth slowing down goes into--get this--hoisting the
moon! That's right. The rotational slowing of the earth results in the
moon being gradually moved into a higher orbit all the time. A
description of this effect appears at:
http://seds.lpl.arizona.edu/nineplanets/nineplanets/luna.html

That page also addresses another point mentioned here: whether any
planets have "stopped rotating". Earth's moon has itself almost
stopped rotating! It has what is called "synchronous rotation",
meaning that it rotates once for each revolution. That is to say, it
always keeps the same face pointed towards the earth, so it rotates
once for each trip around the earth. Most of the satellites in the
solar system rotate synchronously. The drag on rotation from rotating
around a body with such a larger mass has essentially put a brake on
the rotation of the moons in the solar system.

What does all of this have to do with perpetual motion machines? The
very idea of a perpetual motion machine conjures up ideas of a power
source that is inexhaustible. Yet the natural laws that make perpetual
motion machines impossible have to do with the observed fact that
energy can't come from nowhere, and that any net energy transfer
always increases the net disorder in the universe, and therefore
cannot be 100% efficient. So you can't win, and you can't even break
even. Now, this doesn't mean that we can't, at least in theory,
harness energy sources that are virtually inexhaustible. But, as far
as scientists have seen so far, mass and energy have to come from
somewhere, and disorder always increases. The books always balance.

Practically speaking, though, I'd love to see solar, tidal,
geothermal, and solar (including biological) energy sources replace
fossil fuels! That's totally doable technically, but not yet
politically or economically. Some day...

--Mark Johnson