h a l f b a k e r yWarm and Fussy
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This is a development of the "Buchanan-Foucault Generator",
which
seems sufficiently different to warrant a new post, although the
ideas both have a common basis. If you read the previous idea,
you
can probably skip some of what follows.
The basic aim is to find a way of extracting energy
(eg,
electricity)
from the rotational movement of the Earth (serious physicists will
start crying now). Two important points to start with:
1) IT IS NOT AN OVER-UNITY DEVICE. If this produces any power
at
all, it will be taken from the Earth's rotational momentum, like
recovering energy stored in a flywheel. However, since the Earth
is
one big mutha flywheel, there's plenty of energy there.
2) IT PROBABLY DOESN"T WORK. I am very happy to accept that
this
won't work, but I'm more interested in understanding *why* it
won't
work.
OK, so here's the idea. Start with a Powerball (see link). This is
basically a gyroscope set on a gimball inside a ball-shaped
housing,
about the size of a cricket ball. You start the flywheel off with a
string. It's a well-known toy, and if you haven't tried one, you
should.
Once it's spinning, you hold the ball in your hand. Naturally,
because
it's a flywheel, it wants to precess (twist its axis around), and you
can feel this quite strongly.
You now start to "twist" the Powerball. This involves keeping a
tight
grip on it whilst rotating your wrist. (Your forearm stays still;
your
fingertips describe a circle.) This is surprisingly difficult, because
the gyroscope in the Powerball is resisting this twist of its axis.
If you continue to twist the axis in this way, the gyroscope *speeds
up* - this is the purpose of the Powerball. The gyroscope actually
powers (by means of magnets in the spinning disc, and coils in the
housing of the Powerball) a set of flashing LEDs and also the
electronics for a display which shows the speed of the gyroscope.
Please, if you haven't seen or used a Powerball, take my word for
it
regarding all the above. They work fine, are sold in their
millions,
and are great fun.
Now here's where it gets scary.
As far as I can tell, the Powerball is using the twisting energy
supplied by my wrist, and converting it into spinning of the
gyroscope. This is enough to keep the gyroscope spinning and
even
to accelerate it; of course we started by spinning the gyroscope
with
the string, but the twisting accelerates it up to 6-8000rpm, and
will
keep it spinning against friction for as long as you keep twisting
your
wrist. It's also enough to generate a small amount of electricity
for
the LEDs and display.
So. Suppose we go to the North Pole. Here, we erect a vast steel
wrist, firmly fixed to the ground (OK, we might be better off at
the
South Pole - no matter). This wrist holds a Giant Powerball, with
its
axis pointing at about 45 degrees to the vertical.
Just as in the normal Powerball, the cage of the Giant Powerball
holds some coils, and the gyroscope carries some magnets, so that
spinning the gyroscope will generate electricity. (And yes, this
tends
to slow the gyroscope down, so it has to be made to spin, which is
exactly the same as in the normal Powerball).
Now, we start the gyro spinning with a Very Large Piece of String
(as
in the normal powerball). This, of course, is an input of energy, I
know.
Now, the Earth rotates. As it does so, the Giant Wrist turns,
holding
the Giant Powerball. Viewed from space above the North Pole,
the
base of the wrist stays still, while the tips of the fingers (and the
distal end of the Powerball) trace out a circle.
This motion is exactly the same as the movement which my wrist
gives to the normal Powerball. Accordingly, the gyro in the Giant
Powerball should be driven to higher speeds (as it is in the normal
Powerball). It should also generate electricity (as in the normal
Powerball). It will continue to accelerate until the combination of
frictional losses plus the losses which are tapped off as electricity
balance the energy input from the twisting motion (again, exactly
as
in the normal Powerball). It will then continue to spin at this high
speed, and continue to produce electricity (as in the normal
Powerball) for as long as the Giant Wrist continues to twist it,
which
means for as long as the Earth keeps turning.
Again, THIS IS NOT AN OVER UNITY DEVICE!! The Giant Powerball
will tend to slow down the rotation of the Earth (just as the
normal
Powerball tries to oppose the turning of my wrist), and any energy
extracted will be balanced by a slowing of the Earth's rotation.
*****WHY IT WON'T WORK*****
Here I have tried to anticipate the objections. I don't think it
*will*
work, but still don't see why:
A) "It can't work because it's over-unity." No it's not - see last para
above.
B) "I don't think a normal Powerball works." Yes it does.
Seriously,
go buy one, they're fun. You do have to start the gyro at low
speed
with a string, but then (as you will see) you can keep it spinning at
very high speed, and keep it lighting the LEDs, indefinitely if you
keep twisting your wrist.
C) "Conservation of angular momentum." This is probably the key
to
the explanation of why this won't work, but it's not really a
"mechanistic" explanation. Also, momentum need not equate to
energy: you can conserve angular momentum whilst extracting
energy. (Imagine two discs adjacent on a common axle; one
carries
magnets, the other carries coils connected to light bulbs; start
them
spinning in opposite directions; electricity will be generated, and
the
light bulbs will glow; the discs will slow down and stop; total
angular momentum is zero all the way through, yet the *kinetic*
energy of the system has been extracted as light.)
D) "You're putting energy in at the beginning with the giant
string." Yes, we are, exactly as in the normal Powerball. But, in
the normal Powerball, the energy provided by twisting your wrist
speeds up the gyro, and keeps it going indefinitely; the energy
needed to do so is arbitrarily greater than the energy which you
put in by pulling the string to start the gyro working. The
continuous energy output comes from your wrist-power (or, in this
case, from the Earth's turning).
E) "The Earth turns once a day; your wrist turns much faster." Yes,
but that's just a matter of scale. When using a normal Powerball,
you twist your wrist in circles at a rate of maybe once per second
(1Hz), but the Powerball's gyro gets driven up to several thousand
RPM (10-100Hz) - there's a sort of "leverage" effect. In fact, the
faster the gyro, the greater this "leverage" - you can spin the gyro
up to even higher speeds (the record is something lie 15,000rpm,
or 250Hz), not by twisting faster but by twisting with sufficient
force. If you prefer, imagine doing this on a planet which spins
once per second - we'd still be extracting (maybe!) energy from its
rotation.
Powerball
http://en.wikipedia...copic_exercise_tool
[MaxwellBuchanan, Jul 25 2010]
Coriolis Lake Power
Coriolis_20Lake_20Power
Same force, different harness [marklar, Jul 25 2010]
Gyroscope without gimbals
Gyroscope_20without_20gimbals
vaguely related [xaviergisz, Jul 26 2010]
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Annotation:
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It can't work. I don't know why not. |
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Just to address the "friction" aspect as mentioned elsewhere. The end of the shaft is in a groove, and it spins up the ball by rolling the side of the shaft end along the side of the groove. It is small in diameter, so it has to roll fast, which makes the ball turn fast. The gyro forces press the shaft against the wall, allowing it to roll, not just slide, and around and around it goes. It must have friction to get a grip between the side of the shaft and the side of the groove. |
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The thing is not "friction-powered" because that isn't even possible, but it will not work if you grease it. |
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[Not that this has anything to do with the idea itself.] |
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[Voice] I agree with you!! It's the "why not" I'm worried
about. |
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[bacon] I'm happy to agree with that, but it doesn't alter the
point: twisting the Powerball spins it up, taking energy from
the twisting and converting some of it to electricity; I don't
see why a biiiig Powerball, twisted in the same way by being
mounted at an angle at the North Pole, won't do the same
thing. |
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tsh!
Of course it will work. .. until the Earth stops spinning. |
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[disclaimer]
This statement is based soley upon plugging known factors into a Cranial Animated Design program and veiwing the results. It does not necessarily reflect the laws of physics or even the opinion of the owner of said CAD program. |
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I think this would work, but scale is the problem, I
don't know how big it would need to be to do
anything. |
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The good news is, you don't need to visit a pole to
test it, the 'wrist' just needs to be perpendicular
to the poles, because anywhere on Earth rotates
around the axis once per day. |
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Now, to the matter of scale. If you want the
gyroscope to do a modest 1 rpm, the thickness of
the gyroscope axle will need to be 1/1440 (minutes
in a day) of the diameter of the circular rails it sits
between, or a 1cm axle 14.4m long (it only needs
to be 1 cm where it meets the rail). If you want it
to rotate once per second the ratio gets a bit silly
(a 1mm axle 86.4m long) but that's merely a gearing
challenge. |
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Your next problem is finding a mass/friction ratio
that will allow you to gain kinetic energy. That's a
bit beyond me. |
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This is definitely within the realms of possibility,
certainly for a university or science museum. |
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Edit: removed the equator bit. |
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N-ertia N-ergy N-Prize N-yone? |
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//N-ertia N-ergy N-Prize N-yone?//
It's more N-gular mom-N-tum... |
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//I think this would work, but scale is the problem// |
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I think it won't work, and scale isn't the problem. |
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I still don't see why not, but there's a basic issue of
extracting energy from rotation without having a "stator"
which is not rotating (relative to the Earth, in this case).
So it shouldn't work. |
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But if it did work, scale wouldn't matter. It's the principal
that's interesting. |
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//you don't need to visit a pole to test it// Good point.
I'd started with the North Pole because it's easier to
imagine it, but then I forgot that it's only a mental
convenience. Thanks for reminding me. |
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I think there are two ways to possibly steal energy from the Earth's rotation. |
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One involves simply turning an object around using the Earth's rotation--most easily visualized at the poles, but possible everywhere--and snarfling energy out of that somehow using gyroscopes. |
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The other involves Coriolis--two objects far from the axis with a difference in distance from the axis and therefore speeds of travel--best done at ground level in the mid-latitudes or vertically at the equator. |
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This idea is the first kind, obviously. But are the two really different? |
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The gyroscope axle is stationary (or at least it wants
to be). It wouldn't be as mathematically perfect as I
calculated because although it would resist being
rotated by the earth, it would turn with it a bit (or a
lot, probably 99% in practice) because of energy
deliberately extracted and frictional losses. |
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What would Powerball snooker be like? |
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The reason why you can't extract power from the earth's 'rotation' is that you have nothing 'stationary' to react against. |
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If you could mount the giant powerball on a giant arm suspended in space, then you could use the earth's rotation to twist it. |
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Without the giant arm, you can't generate the twist. |
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//The reason why you can't extract power from the earth's
'rotation' is that you have nothing 'stationary' to react
against.// |
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Yes, I agree, but that is not a "mechanistic" explanation. |
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The question boils down to this: what is the fundamental
difference between me rotating the Powerball with my
wrist, and the Earth's spin rotating the Powerball? |
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In the former case, energy from my wrist is translated into
energy in the Powerball (faster spin; electricity production
to light the LEDs), without there being anything to "react
against" in the sense you mean. |
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So, how does the latter case differ? |
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I'm happy to accept it won't work, but I want to know why,
in terms of forces. |
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In the first case, you are reacting against the earth. |
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When you initially spin up the gyro, it is not stationary. It is rotating with the Earth, about the Earths axis, also around the Sun, etc. This is your initial frame of reference. |
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When you move it with you wrist, you are standing on your frame of reference (Earth) and moving it relative to that. |
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When you spin up your giant gyro, it is stationary relative to Earth. |
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I don't think that's the case. I am fairly sure that I can, for
example, sit on a swivelly chair and make the Powerball
work. I am also pretty sure that I could make the
Powerball work if I were in space, or anywhere else. |
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(I have just tested the first of those; no problem. If
anyone will sponsor me to try the second, I am ready.) |
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Of course, if I am in space (or on a really good swivel
chair), then using the Powerball would tend to make me
turn in the opposite direction, but that is the whole point:
there's a reaction between me and the Powerball. |
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I think the difference between turning your wrist
and the earth turning is that the earth keeps
turning at the same speed in the same direction. |
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It is the direction and constant axis I think would
be important for the powerball. |
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I noticed wikipedia says turning it in the plane of
the grooves doesn't accelerate.
It also seems like turning it in the internal
gyroscopes plane of rotation wouldn't accelerate
it. |
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My guess is that if you got it going, then mounted
it on something that always spins in the same
direction, the internal gyroscope's plane of
rotation would end up matching the mount's
rotation. |
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Or as a quick test, try just turning it one way, and
see if it approaches one of those dead zones (you
may not manage to keep the rotation perfectly in
the same axis, in which case it won't be exactly at
the dead zone and may still work) |
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edit: a bit more I thought after I posted: |
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let me know the result of the hand turn test, I
want to know. |
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I've got an argument for why the axis of the
internal gyroscope should approach the axis of
external rotation:
when you rotate it in a particular direction, part of
the force is torque in that direction, so it should
get more rotation in that direction (which means
turning its axis of rotation towards where it would
rotate the same way as the applied torque).
That's not the only component of force you'd apply
to rotate it, you'd also be resisting the gyroscopic
reactions, but I think its still applies. |
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//I think the difference between turning your wrist and
the earth turning is that the earth keeps turning at the
same speed in the same direction. // |
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I think you may be right, but I'm not sure I understood
exactly what you mean. |
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I realized there is a difference between the wrist-held
powerball and one mounted on a "wrist" at the north pole.
When I turn my wrist (and assume for this analogy that my
forearm is pointing upwards - a la North Pole), my index
finger (say) is always closest to my face; the nail of my
index finger always faces my face (more or less). In other
words, although the tip of my index finger describes a
circle, my hand isn't actually rotating. |
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In contrast, the mechanical "hand" actually does rotate,
and if we equipped it with an index finger and fingernail,
that fingernail would face first the sun, then away from
the sun. |
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I'm not sure if this is of any significance, but it's the only
qualitative difference I can see between my wrist and a
mechanical wrist at the North Pole. |
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The key experiment would be to build a "wrist" to hold the
ball at an angle, then mount it on a record turntable and
see if it could spin up the gyro... |
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//North Pole. Here, we erect a vast steel wrist, firmly fixed to the ground |
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Only if it is capable of two-fingered salute to passing ufo's. |
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Hang on, you could do a pyrkete hand.. |
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// I'm not sure if this is of any significance, but it's the only qualitative difference I can see // |
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Yes, this is the significant difference. The powerball accelerates when you apply a tipping motion that follows the axis of the gyro as it rotates in the track. Actual rotation of the ball is basically irrelevant. If the circular track that holds the axle of the gyro is horizontal so the axis of the spinning gyro is also horizontal, if you try to tip it so that it lifts one end of the axle and lowers the other, the axle will be pushed against the top of the track on one end and the bottom of the track on the other. The rolling of the axles on the sides of the track will be in the same direction that the axle is being moved by the precession cause by the same force on the axles. If the torque applied to tip it is strong enough, the precession will be faster than the rolling, so the spinning speed will increase. But as the axis precesses, the direction of tipping force needs to be change so that the axis of the applied torque is 90 degrees from the axis of axle rotation. That is why a circular tilting motion is used to speed up the powerball. |
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If you set up your powerball with the track at 45 degrees at the north pole and start out with your gyro axis horizontal, as the earth rotates, there will be a component of torque on the axis that will cause the gyro to speed up, but as it reached the top/bottom where the axis is at 45 degrees, there will be no more precession. If you force the axis to move past that point, the torque caused by the earth rotation will cause precession in the opposite direction, back towards the stable 45 degree point. It’s maybe easier to visualize if you make the circular track stand on edge (90 degrees rather than 45). When the gyro axis is horizontal, precession causes the axis to rotate until the axis is vertical. If it somehow went past vertical, the precession would be in the other direction. If the track was flat, then rotation could cause some force because of friction which would cause precession that would cause more friction on one side than the other, causing the axle to rotate in the same direction that the track is being rotated. The 45 degree case is a superposition of those two things. |
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A similar system is a marble on a plate. By tipping the plate in a circular motion, you can accelerate the marble and make it spin faster and faster. Once it’s spinning you can actually simplify the motion to just tipping side to side. But if you simply placed the marble on an angled plate on top of a turntable, it won’t accelerate. The powerball is comparatively cool because you aren’t relying on the relatively weak force of gravity, so you can put a lot more energy into it. |
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This idea can’t work because you can’t create a forcefully tilting platform using only the earth. You need a stator. But this doesn’t make the accounting for the conservation of angular momentum any clearer. With the plate, all you are doing is tipping it side to side and the marble is gaining angular momentum. How is the opposite angular momentum applied to the earth? I suspect this is easier to explain with a marble than a powerball, but I’ll leave that alone for a minute. |
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So, really we just need a gigantic marble and plate...I suggest pyrkrete (spelling?) |
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If you use the Earth as the marble you only need to make the plate. |
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I like the idea of a scaled down experiment using a record turntable. My bet is that it won't work - but I'm not betting anything which I can't afford to lose. |
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[scad] The tipping of the plate and the rolling of the
marble are out of phase with each other. This means
that the marble is effectively rolling downhill, which
both accelerates the marble, and requires that, while
the plate may be rocked purely about a horizontal
axis, a torque component about a vertical axis is
nonetheless applied to the plate, and its opposite is
applied to the earth. |
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I like this idea, and I see no reason why it won't
work, though gyroscope equations make my head
hurt so I'll save this project for another time. People
being what they are, I predict angular momentum
conservation becomes a "cause" at about the same
time the oil runs out. |
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Actually, a "Conserve angular momentum" pressure group, with bumper stickers and t-shirts, etc. would be a great idea. |
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//I like this idea, and I see no reason why it won't
work,// |
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I like it too, and I see no reason why it won't work,
but it won't work. It can't. |
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We're tapping off some of the earth's angular
momentum to generate electricity. So, if we
imagine putting a big box around the earth (with
plenty of room), then the total angular
momentum inside the box is decreasing, which it
can't be allowed to do. |
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That's why you need the external stator - the
angular momentum lost by one thing is gained by
the other. |
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But I still don't understand _how_ this will fail. |
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Executive summary for the hard of reading: take a
big powerball, strap it to the north pole, see what it
does. |
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