Tidal gererators
Tim Lamb
R4 was explaining how generators installed in tide races work, this
evening. An idle thought nervously tip-toed through my brain...
If we utilise energy created by the effect of the Moon's gravity
will we interfere with its orbital velocity over the next billion years?
Regards
--
Tim Lamb
Oz
> If we utilise energy created by the effect of the Moon's gravity
>will we interfere with its orbital velocity over the next billion years?
You do think long term, a billion years ....
Perhaps you might consider a smaller timescale like, say, 1M yrs?
That's quite a long way in human advancement (ag 20,000, industry
300...).
--
Oz
This post is worth absolutely nothing and is probably fallacious.
BTOPENWORLD address about to cease. DEMON address no longer in use.
>>Use o...@farmeroz.port995.com<<
ozac...@despammed.com still functions.
Jim Webster
"Tim Lamb" <t...@marford.demon.co.uk> wrote in message
news:jVMoLAAp...@marford.demon.co.uk...
Wind turbines will also increase day length by slowing down rotation.
Actually they are talking about sticking a lot of tidal generators across
Morecambe Bay with a road over the top, and it is supposed to be about ten
years off, but the environmental groups are getting themselves nicely wound
up and I suspect that it will remain ten years off, (A road bridge has been
ten years off all my life)
Jim Webster
Charles Francis
<t...@marford.demon.co.uk> writes
already, all we would be doing is creaming off a little of it on the
way. The net result, that the tides apply a drag on the earths rotation
causing the length of day to increase is going on all the time. I don't
think we would be affecting it. At least I don't think so this morning.
Regards
--
Charles Francis
Tim Lamb
<cha...@clef.demon.co.uk> writes
>> If we utilise energy created by the effect of the Moon's gravity
>>will we interfere with its orbital velocity over the next billion years?
>>
>>
>I don't think so. The energy in the tides gets dissipated as heat
>already, all we would be doing is creaming off a little of it on the
>way. The net result, that the tides apply a drag on the earths rotation
>causing the length of day to increase is going on all the time. I don't
>think we would be affecting it. At least I don't think so this morning.
Umm.. I was taught to look for extreme cases in doubtful situations.
Suppose the Earth had no continents or other obstructions such that the
*ocean* could eventually rotate at the same speed as the Moon and you
then stick a row of generators across the equator?
Are you then not withdrawing energy directly from the Moon?
regards
--
Tim Lamb
Charles Francis
<t...@marford.demon.co.uk> writes
rotation about its axis. Superficially the rate of dissipation appears
greater if you put in the generators, just as it appears greater when
you put in the continents, but my guess is that if there are no
obstructions the mass of flowing water would be so much larger that it
would lose energy faster for that reason. So no real guesses. Whichever
way you look at it there is a drag on the earths rotation, and more than
that cannot be said without going into detail modelling and calculation
Regards
--
Charles Francis
Derek Moody
Derek Moody
Gravity works both ways. Anything that slows the tidal bulge applies a drag
to the larger system.
grey...@yahoo.com
There was a sarcastic song a few years ago about the decline in
Austraila's environment. Went some way like
"What are they worried about?. Australia is good for at least ten years
yet!"
--
greymaus
Al Firan RumaiDin
97.025% of statistics are wrong
Charles Francis
<de...@farm-direct.co.uk> writes
without slowing it any more.
Regards
--
Charles Francis
Edward
"Jim Webster" <J...@zerospam.mok.net> wrote:
Sounds like the Severn Barrage. It's been a good idea since before the
war.
If we install more wind farms, will it get windier? Farms are for
producing things aren't they?
I happened to be looking at a 1974 Reader's Digest yeserday. An article
about climate was warning about the poor outlook we could expect in the
near future because of global cooling!! :*)
Edward..
Jim Webster
"Edward" <edd...@invalid.org.uk> wrote in message
news:086133d6...@freeuk.com...
> In message <cea5c9$snr$7...@news6.svr.pol.co.uk>
> "Jim Webster" <J...@zerospam.mok.net> wrote:
>
> >
> > "Tim Lamb" <t...@marford.demon.co.uk> wrote in message
> > news:jVMoLAAp...@marford.demon.co.uk...
> > > In the interests of diverting the *deadly apples* thread....
> > >
> > > R4 was explaining how generators installed in tide races work, this
> > > evening. An idle thought nervously tip-toed through my brain...
> > >
> > > If we utilise energy created by the effect of the Moon's
gravity
> > > will we interfere with its orbital velocity over the next billion
years?
> > >
> >
> > Wind turbines will also increase day length by slowing down rotation.
> >
> > Actually they are talking about sticking a lot of tidal generators
across
> > Morecambe Bay with a road over the top, and it is supposed to be about
ten
> > years off, but the environmental groups are getting themselves nicely
wound
> > up and I suspect that it will remain ten years off, (A road bridge has
been
> > ten years off all my life)
> >
> > Jim Webster
> >
> >
> Sounds like the Severn Barrage. It's been a good idea since before the
> war.
that's the one, same thing
>
> If we install more wind farms, will it get windier? Farms are for
> producing things aren't they?
sign me up for a money farm then
>
> I happened to be looking at a 1974 Reader's Digest yeserday. An article
> about climate was warning about the poor outlook we could expect in the
> near future because of global cooling!! :*)
>
Yes my 69 RD atlas talks of the coming iceage!!
Jim Webster
Derek Moody
<URL:mailto:cha...@clef.demon.co.uk> wrote:
> In message <ant29133...@half-baked-idea.co.uk>, Derek Moody
> <de...@farm-direct.co.uk> writes
> >Gravity works both ways. Anything that slows the tidal bulge applies a drag
> >to the larger system.
> >
> The continents already slow the tidal bulge. You could draw off energy
> without slowing it any more.
Unless you are slowing it you cannot collect any of its energy.
Continents do impede the flow and degrade the energy to heat.
The effect of your turbines may be infinitesimal in relation to continental
impedence but it not zero.
At periods when there were no equatorial landmasses the tide must have
flowed more freely (and may again), at these times the Earth moon co-orbit
must have ben affected less. I wonder if there is any evidence...
Derek Moody
<URL:mailto:stu...@zetnet.co.uk> wrote:
> The message <$vNPVAAu...@marford.demon.co.uk>
> from Tim Lamb <t...@marford.demon.co.uk> contains these words:
>
> > Suppose the Earth had no continents or other obstructions such that the
> > *ocean* could eventually rotate at the same speed as the Moon and you
> > then stick a row of generators across the equator?
> > Are you then not withdrawing energy directly from the Moon?
>
> the moon (and sun, of course) is the cause of tides, and the tides are
> the effect of the gravitational pull.
>
> Thus if you impede the present effect, that has no bearing upon the cause
> as there is no feedback to the moon and sun by the effect. It is surely the
> total mass of respectively, the earth, moon and sun that keeps the planet
> and sattelite in fixed orbit.
Water has mass. The tidal bulge lags the moon, if delayed by obstructions
it will lag a little more and feedback its own gravity into the equation.
The apparent symmetry of the tidal bulge doesn't cancel btw as the
relationship is inverse square and not linear.
> In the same way, if every roof in the world was tiled with PV panels,
> the net gain of energy from the sun would not diminish the star in any
> way at all, as there is no relationship between drawing energy from the
> sun and its production of energy, but simply a dependance upon the
> sun to produce energy.
This however is true, the panel interrupts the energy on its route to heat
but it still gets there. There -could- be a tiny amount of feedback though.
The reflected light from the Earth that gets back to the sun is not zero. A
change in albedo could in theory have some effect. I wouldn't worry
overmuch about it though...
Charles Francis
>In article <OcsQ8aBBGVCBFw$N...@clef.demon.co.uk>, Charles Francis
><URL:mailto:cha...@clef.demon.co.uk> wrote:
>> In message <ant29133...@half-baked-idea.co.uk>, Derek Moody
>> <de...@farm-direct.co.uk> writes
>
>> >Gravity works both ways. Anything that slows the tidal bulge applies a drag
>> >to the larger system.
>> >
>> The continents already slow the tidal bulge. You could draw off energy
>> without slowing it any more.
>
>Unless you are slowing it you cannot collect any of its energy.
>
>Continents do impede the flow and degrade the energy to heat.
>
>The effect of your turbines may be infinitesimal in relation to continental
>impedence but it not zero.
Not necessarily. You may be simply drawing off some of the energy before
it gets turned to heat. In fact in all the systems I know that is
precisely what happens. The water going in an out of an estuary. It has
to turn round and go back the way it came, whether you have the tidal
barrage or not. So having the tidal barrage isn't going to take any
energy that's not on its way to becoming heat already.
>
>At periods when there were no equatorial landmasses the tide must have
>flowed more freely (and may again), at these times the Earth moon co-orbit
>must have ben affected less. I wonder if there is any evidence...
>
I have heard of evidence that the earth has slowed down. Nothing about
changes in the rate of slowing.
Regards
--
Charles Francis
Charles Francis
<stu...@zetnet.co.uk> writes
>The message <EoGSREzr...@clef.demon.co.uk>
>from Charles Francis <cha...@clef.demon.co.uk> contains these words:
>
>> Well the energy is coming not from the moon, but from the earths
>> rotation about its axis.
>
>
>The energy taken from tides is simply the utilisation of heads of
>water either side of a barrage which is fitted with sluice generators
>that work both ways. Thus one generates electricity at high tide,
>filling an empty basin, and at low tide, emptying a full basin.
>
>The cause of tides is the gravitational attraction of the moon and
>sun. There are spring tides when the moon and sun pull together
>or are diametrically oposite to one another, and neap tides when
>this is not the case.
Yes. All of that is right. But the two tides per day are due to the
elongation of the water in the direction of the moons pull. This
elongation rotates about the earth as the earth spins on its axis. So
the energy used/dissipated comes from the spinning of the earth.
Regards
--
Charles Francis
Oz
>Yes. All of that is right. But the two tides per day are due to the elongation
>of the water in the direction of the moons pull. This elongation rotates about
>the earth as the earth spins on its axis. So the energy used/dissipated comes
>from the spinning of the earth.
That's not quite right. Conservation of angular momentum and all that.
The moon is as a consequence moving slowly away from us.
IIRC it was once half the distance it is now.
At some point the earth will stop rotating wrt the moon and this effect
will cease, although then we still have to consider the tides due to the
sun. Typically this sort of system ends in an integral orbital/rotation
relationship.
Oz
>
>Not necessarily. You may be simply drawing off some of the energy before it gets
>turned to heat. In fact in all the systems I know that is precisely what
>happens. The water going in an out of an estuary. It has to turn round and go
>back the way it came, whether you have the tidal barrage or not. So having the
>tidal barrage isn't going to take any energy that's not on its way to becoming
>heat already.
There are standing waves set up, IIRC these need to be considered when
predicting tide tables. So some of the wave motion is oscillatory and
thus non-dissipative.
Charles Francis
<o...@farmeroz.port995.com> writes
>Charles Francis <cha...@clef.demon.co.uk> writes
>>Yes. All of that is right. But the two tides per day are due to the
>>elongation
>>of the water in the direction of the moons pull. This elongation
>>rotates about
>>the earth as the earth spins on its axis. So the energy used/dissipated comes
>>from the spinning of the earth.
>
>That's not quite right.
It's right. It's just not complete.
>Conservation of angular momentum and all that.
Yes. The slowing down of the earths rotation must be matched by an
increase in the moons angular momentum. .Interesting that the tidal
forces have this effect of dragging the moon, so that it accelerates.
>The moon is as a consequence moving slowly away from us.
Yes. If the moon accelerates it moves into a higher orbit, where, of
course it ends up going more slowly. But greater angular momentum due to
distance.
>
>IIRC it was once half the distance it is now.
Goodness. I didn't know that.
Regards
--
Charles Francis
Charles Francis
<o...@farmeroz.port995.com> writes
>Charles Francis <cha...@clef.demon.co.uk> writes
>>
>>Not necessarily. You may be simply drawing off some of the energy
>>before it gets
>>turned to heat. In fact in all the systems I know that is precisely what
>>happens. The water going in an out of an estuary. It has to turn round and go
>>back the way it came, whether you have the tidal barrage or not. So
>>having the
>>tidal barrage isn't going to take any energy that's not on its way to
>>becoming
>>heat already.
>
>There are standing waves set up, IIRC these need to be considered when
>predicting tide tables.
You mean like at Poole & places on the south coast where there are four
tides? Poor place for a tidal barrage. Tides are rather low there.
>So some of the wave motion is oscillatory and
>thus non-dissipative.
>
I don't think it would be at an ideal site, somewhere facing straight
out into the Atlantic, like the Severn estuary.
Regards
--
Charles Francis
Derek Moody
<URL:mailto:cha...@clef.demon.co.uk> wrote:
> >The cause of tides is the gravitational attraction of the moon and
> >sun. There are spring tides when the moon and sun pull together
> >or are diametrically oposite to one another, and neap tides when
> >this is not the case.
>
> Yes. All of that is right. But the two tides per day are due to the
> elongation of the water in the direction of the moons pull. This
> elongation rotates about the earth as the earth spins on its axis. So
> the energy used/dissipated comes from the spinning of the earth.
And a fraction must be diverted into the co-orbit.
Derek Moody
<URL:mailto:cha...@clef.demon.co.uk> wrote:
> In message <ant30090...@half-baked-idea.co.uk>, Derek Moody
> <de...@farm-direct.co.uk> writes
> >In article <OcsQ8aBBGVCBFw$N...@clef.demon.co.uk>, Charles Francis
> ><URL:mailto:cha...@clef.demon.co.uk> wrote:
> >> In message <ant29133...@half-baked-idea.co.uk>, Derek Moody
> >> <de...@farm-direct.co.uk> writes
> >
> >> >Gravity works both ways. Anything that slows the tidal bulge applies a drag
> >> >to the larger system.
> >> >
> >> The continents already slow the tidal bulge. You could draw off energy
> >> without slowing it any more.
> >
> >Unless you are slowing it you cannot collect any of its energy.
> >
> >Continents do impede the flow and degrade the energy to heat.
> >
> >The effect of your turbines may be infinitesimal in relation to continental
> >impedence but it not zero.
>
> Not necessarily. You may be simply drawing off some of the energy before
> it gets turned to heat. In fact in all the systems I know that is
> precisely what happens. The water going in an out of an estuary. It has
> to turn round and go back the way it came, whether you have the tidal
> barrage or not. So having the tidal barrage isn't going to take any
> energy that's not on its way to becoming heat already.
But you have a mass of water being held back (even if only slightly) from
it's natural position. It has its own gravity. There is the feedback
mechanism.
> >At periods when there were no equatorial landmasses the tide must have
> >flowed more freely (and may again), at these times the Earth moon co-orbit
> >must have ben affected less. I wonder if there is any evidence...
> >
> I have heard of evidence that the earth has slowed down. Nothing about
> changes in the rate of slowing.
Not going to be easy to measure - I wonder where to look for the evidence.
Derek Moody
<URL:mailto:cha...@clef.demon.co.uk> wrote:
> In message <WJNa6wC3...@farmeroz.port995.com>, Oz
> <o...@farmeroz.port995.com> writes
> >There are standing waves set up, IIRC these need to be considered when
> >predicting tide tables.
>
> You mean like at Poole & places on the south coast where there are four
> tides? Poor place for a tidal barrage. Tides are rather low there.
Waddya mean low? Most of them have over 20cm rise/fall. OK I have seen a low
tide higher than the previous high tide when neaps coincided with a frontal
trough but that's fairly unusual.
> >So some of the wave motion is oscillatory and
> >thus non-dissipative.
> >
> I don't think it would be at an ideal site, somewhere facing straight
> out into the Atlantic, like the Severn estuary.
Are you generating from a head or operating a turbine in a tidal stream?
Tidal nodes lie in the places between those with large rise/fall. All that
water at high tide has to go somehwere - it all shunts along a bit and piles
up as high tide somewhere else before (mostly) coming back again (on a
looped route). Tidal nodes have little rise and fall but considerable tidal
streams. Iow tidal nodes are prime sites for tidal stream turbines.
Oz
>>oz:
>>IIRC it was once half the distance it is now.
>
>Goodness. I didn't know that.
<Oz faints>
Charles Francis
<de...@farm-direct.co.uk> writes
>In article <Xg2WTsUp...@clef.demon.co.uk>, Charles Francis
><URL:mailto:cha...@clef.demon.co.uk> wrote:
>> In message <WJNa6wC3...@farmeroz.port995.com>, Oz
>> <o...@farmeroz.port995.com> writes
>
>> >There are standing waves set up, IIRC these need to be considered when
>> >predicting tide tables.
>>
>> You mean like at Poole & places on the south coast where there are four
>> tides? Poor place for a tidal barrage. Tides are rather low there.
>
>Waddya mean low? Most of them have over 20cm rise/fall. OK I have seen a low
>tide higher than the previous high tide when neaps coincided with a frontal
>trough but that's fairly unusual.
>
>> >So some of the wave motion is oscillatory and
>> >thus non-dissipative.
>> >
>> I don't think it would be at an ideal site, somewhere facing straight
>> out into the Atlantic, like the Severn estuary.
>
>Are you generating from a head or operating a turbine in a tidal stream?
I was thinking of systems operating from a head
Regards
--
Charles Francis
Charles Francis
<de...@farm-direct.co.uk> writes
Yes, but as we have seen this diverts more energy from the spin of the
earth into the moons orbit, rather than taking energy from the moon
>
Regards
--
Charles Francis
Jim Webster
"Charles Francis" <cha...@clef.demon.co.uk> wrote in message
news:Xg2WTsUp...@clef.demon.co.uk...
or apparently Morecambe bay.
Jim Webster
Jim Webster
"Derek Moody" <de...@farm-direct.co.uk> wrote in message
news:ant30234...@half-baked-idea.co.uk...
> In article <Xg2WTsUp...@clef.demon.co.uk>, Charles Francis
> <URL:mailto:cha...@clef.demon.co.uk> wrote:
> > In message <WJNa6wC3...@farmeroz.port995.com>, Oz
> > <o...@farmeroz.port995.com> writes
>
> > >There are standing waves set up, IIRC these need to be considered when
> > >predicting tide tables.
> >
> > You mean like at Poole & places on the south coast where there are four
> > tides? Poor place for a tidal barrage. Tides are rather low there.
>
> Waddya mean low? Most of them have over 20cm rise/fall. OK I have seen a
low
> tide higher than the previous high tide when neaps coincided with a
frontal
> trough but that's fairly unusual.
>
> > >So some of the wave motion is oscillatory and
> > >thus non-dissipative.
> > >
> > I don't think it would be at an ideal site, somewhere facing straight
> > out into the Atlantic, like the Severn estuary.
>
> Are you generating from a head or operating a turbine in a tidal stream?
the current planning for Morecambe Bay is for turbines but with one single,
vertically suspended blade
Jim Webster
Oz
>the current planning for Morecambe Bay is for turbines but with one single,
>vertically suspended blade
Would this be a useful alternative to the church door?
Charles Francis
<o...@farmeroz.port995.com> writes
>Jim Webster <J...@zerospam.mok.net> writes
>
>>the current planning for Morecambe Bay is for turbines but with one single,
>>vertically suspended blade
>
>Would this be a useful alternative to the church door?
>
enough energy to make it worth attaching a turbine to the church door.
Regards
--
Charles Francis
Oz
Jim Webster
"Oz" <o...@farmeroz.port995.com> wrote in message
news:Fg1Ow2DU...@farmeroz.port995.com...
> Jim Webster <J...@zerospam.mok.net> writes
>
> >the current planning for Morecambe Bay is for turbines but with one
single,
> >vertically suspended blade
>
> Would this be a useful alternative to the church door?
unlike the conventional turbine it doesn't dice and slice anything going
through it, but depending upon tide levels and door heights there is
obviously potential.
Not sure of the material, we may have to revisit the thread about nails and
fixatives
Jim Webster
Jim Webster
> Charles Francis <cha...@clef.demon.co.uk> writes
> >In message <Fg1Ow2DU...@farmeroz.port995.com>, Oz
<o...@farmeroz.port995.com>
> >writes
> >>Jim Webster <J...@zerospam.mok.net> writes
> >>
> >>>the current planning for Morecambe Bay is for turbines but with one
single,
> >>>vertically suspended blade
> >>
> >>Would this be a useful alternative to the church door?
> >>
> >In these godless times, the congregation isn't large enough to supply
enough
> >energy to make it worth attaching a turbine to the church door.
>
> <sigh>
>
> Attaching miscreants to turbine ....
>
actually I think Charles suggestion has merit in itself, although you would
perhaps have to use the door to the gents in a busy public house
Jim Webster
Howard Neil
And a small turbine in the drains?
--
Howard Neil
Charles Francis
Howard Neil <hn...@REMOVETOREPLY.co.uk> writes
of verbal diarrhoea
Regards
--
Charles Francis
Jim Webster
"Howard Neil" <hn...@REMOVETOREPLY.co.uk> wrote in message
news:410b6c86$0$19133$ed26...@ptn-nntp-reader03.plus.net...
next to the handle that reads 'flush twice, it is a long way to the bar'?
Jim Webster
Derek Moody
<URL:mailto:cha...@clef.demon.co.uk> wrote:
> In message <ant30234...@half-baked-idea.co.uk>, Derek Moody
> <de...@farm-direct.co.uk> writes
> >Are you generating from a head or operating a turbine in a tidal stream?
>
>
> I was thinking of systems operating from a head
The unsightly geological hammer version...
Sea-bed tidal-flow turbines have many fewer side effects.
A head requires some sort of dam. A large area of water is held out of
phase with the tide and interferes with littoral habitats, fish movements
and navigation.
More important in the long term may be the twice daily stress variations
exerted by millions of tons of water on undelying strata that are given no
assistance by lunar gravity.
Derek Moody
<URL:mailto:cha...@clef.demon.co.uk> wrote:
> In message <ant30222...@half-baked-idea.co.uk>, Derek Moody
> <de...@farm-direct.co.uk> writes
> >> Yes. All of that is right. But the two tides per day are due to the
> >> elongation of the water in the direction of the moons pull. This
> >> elongation rotates about the earth as the earth spins on its axis. So
> >> the energy used/dissipated comes from the spinning of the earth.
> >
> >And a fraction must be diverted into the co-orbit.
>
> Yes, but as we have seen this diverts more energy from the spin of the
> earth into the moons orbit, rather than taking energy from the moon
Which neatly answers the OP's question which was:
: If we utilise energy created by the effect of the Moon's gravity
: will we interfere with its orbital velocity over the next billion years?
Tim Lamb
<de...@farm-direct.co.uk> writes
>In article <FvZig3XU...@clef.demon.co.uk>, Charles Francis
><URL:mailto:cha...@clef.demon.co.uk> wrote:
>> In message <ant30222...@half-baked-idea.co.uk>, Derek Moody
>> <de...@farm-direct.co.uk> writes
>
>> >> Yes. All of that is right. But the two tides per day are due to the
>> >> elongation of the water in the direction of the moons pull. This
>> >> elongation rotates about the earth as the earth spins on its axis. So
>> >> the energy used/dissipated comes from the spinning of the earth.
>> >
>> >And a fraction must be diverted into the co-orbit.
>>
>> Yes, but as we have seen this diverts more energy from the spin of the
>> earth into the moons orbit, rather than taking energy from the moon
>
>Which neatly answers the OP's question which was:
>
>: If we utilise energy created by the effect of the Moon's gravity
>: will we interfere with its orbital velocity over the next billion years?
And, more importantly, diverts effort away from the Deadly apples
thread:-)
As a student of news group evolution, I long ago lost hope that we would
develop any sense of topic discipline and decided that any *net nanny*
activity would be ignored.
This leaves the area of *spoofing* or diversion open. The technique is
to spot the principle proponents of the multiple thread and put up a
subject likely to test their intellect.
Confession is good for the soul:-)
regards
--
Tim Lamb
Hamisch
> IIRC it was once half the distance it is now.
Well since it appears the moon came out of the earth, it must have been in
all ranges between zero and where it is now.
So your 'If I Remember Correctly' must refer to a personnal memory of a
specific distance. You are old Oz, very old.
Oz
>Well since it appears the moon came out of the earth, it must have been in
>all ranges between zero and where it is now.
I don't think one can really describe a collision with a body about the
size of mars as 'came out of the earth'.
It seems to be generally accepted that when this happened the cores
merged and a significant (much more than moon-sized) amount of
vapourised rock and general debris left the earth at considerable speed.
Most of this eventually made a (closer) moon or rained back on earth.
So the moon actually *formed* some distance away from earth. IIRC about
half the current distance. There is apparently some evidence for this
based on the relationship between the number of tides in a year which
can be determined in some archaic fossil records.
>So your 'If I Remember Correctly' must refer to a personnal memory of a
>specific distance. You are old Oz, very old.
Hmmm.....
I suppose you wouldn't be convinced if I claimed this was a memory of an
article on lunar formation, would you?
Jim Webster
"Tim Lamb" <t...@marford.demon.co.uk> wrote in message
news:JeiSpDAV...@marford.demon.co.uk...
the fact that my contribution to this thread has been mainly concerned about
the crucifixion opportunities then that may speak volumes
Jim Webster
Charles Francis
<o...@farmeroz.port995.com> writes
>I suppose you wouldn't be convinced if I claimed this was a memory of
>an article on lunar formation, would you?
>
in those days?
Regards
--
Charles Francis
Oz
Michelle Fulton
> And, more importantly, diverts effort away from the Deadly apples
> thread:-)
LOL :-) I love it!
> As a student of news group evolution, I long ago lost hope that we
> would develop any sense of topic discipline and decided that any *net
> nanny* activity would be ignored.
>
> This leaves the area of *spoofing* or diversion open. The technique is
> to spot the principle proponents of the multiple thread and put up a
> subject likely to test their intellect.
>
> Confession is good for the soul:-)
This was an interesting convo to read. Thought provoking, anyway. Thanks,
Tim :-)
--
Michelle
Fort Worth, Texas, USA
Life is short. Be determined to enjoy every minute of it :-)
Old Codger
news:ceietk$86g$1$830f...@news.demon.co.uk
> You are old Oz, very old.
That might explain a great deal.
--
Old Codger
e-mail use reply to field
What matters in politics is not what happens, but what you can make people
believe has happened. [Janet Daley 27/8/2003]
Derek Moody
<URL:mailto:t...@marford.demon.co.uk> wrote:
> And, more importantly, diverts effort away from the Deadly apples
> thread:-)
>
> As a student of news group evolution, I long ago lost hope that we would
> develop any sense of topic discipline and decided that any *net nanny*
> activity would be ignored.
>
> This leaves the area of *spoofing* or diversion open. The technique is
> to spot the principle proponents of the multiple thread and put up a
> subject likely to test their intellect.
But I wasn't in the DA thread...
Oz
>The message <WJNa6wC3...@farmeroz.port995.com>
>from Oz <o...@farmeroz.port995.com> contains these words:
>
>> There are standing waves set up, IIRC these need to be considered when
>> predicting tide tables. So some of the wave motion is oscillatory and
>> thus non-dissipative.
>
>Tides may only be predicted in mean conditions. Predictions have
>historically been far exceeded due to the efffects of prolonged wind
>which
>have produced excessive tidal surges, such as the devastating spring tide
>that occurred some time in 1952 or thereabouts.
If you slosh the atlantic you will get standing waves. Just like an
organ pipe this depends on the speed of waves in the sea and the
distance between the shores.
Now it not something I have delved deep into, rather I put my toe in,
but tides also generate waves. When the high tide bumps into the states
it can go no further and REFLECTS part of the energy. Now some deepwater
wave can move surprisingly fast. Some of you may have seen the programs
about earthquakes/landslips on one side of the pacific (ok big ones)
moving long distances very quickly to give tidal waves on the other
side.
Much the same apparently happens in tides. So you have to make various
second order allowances for tidal reflection to give the local result.
That is, tides are far from 100% dissipative.
The total energy in a tide is, however, pretty immense. Perhaps charles
would like to estimate it for the world?
Jim Webster
"Gerald L R Stubbs" <stu...@zetnet.co.uk> wrote in message
news:200408020...@zetnet.co.uk...
> The message <AXFjuYRm...@clef.demon.co.uk>
> from Charles Francis <cha...@clef.demon.co.uk> contains these words:
> > In message <200407292...@zetnet.co.uk>, Gerald L R Stubbs
> > <stu...@zetnet.co.uk> writes
>
> > >The cause of tides is the gravitational attraction of the moon and
> > >sun. There are spring tides when the moon and sun pull together
> > >or are diametrically oposite to one another, and neap tides when
> > >this is not the case.
>
> > Yes. All of that is right. But the two tides per day are due to the
> > elongation of the water in the direction of the moons pull. This
> > elongation rotates about the earth as the earth spins on its axis. So
> > the energy used/dissipated comes from the spinning of the earth.
>
> it before replying. Apart from the earth's axial rotation, does not the
> moon also orbit the earth ?
the moon and earth also rotate in relation to reach other, from memory,
because of their relative masses, the point about the move is actually
inside the earth but comparatively mear the surface
Jim Webster
Jim Webster
> from "Jim Webster" <J...@zerospam.mok.net> contains these words:
>
> > or apparently Morecambe bay.
>
> Morcambe bay does not have a decent head of water. The tide comes in
> very quickly because the fall of the sea bottom is very slight.
> Hunstanton, on the
> Wash, is very similar.
Because of the nature of the turbines, it isn't the head that is the factor
that makes the site interesting, but the fact that the tide is almost
constantly either coming in or going out and an awful lot of water flows
through them during the course of a day
Effectively they seem to be swapping quality (head) for quantity (width).
The reasons for this are they aren't allowed to meaningfully delay the
passage of the water (otherwise they could cause backing up/flooding etc)
and also because the turbines turn comparatively slowly meaning that they do
not mince such things as seals, swimmers etc.
Jim Webster
Oz
>Because of the nature of the turbines, it isn't the head that is the factor
>that makes the site interesting, but the fact that the tide is almost
>constantly either coming in or going out and an awful lot of water flows
>through them during the course of a day
>Effectively they seem to be swapping quality (head) for quantity (width).
>The reasons for this are they aren't allowed to meaningfully delay the
>passage of the water (otherwise they could cause backing up/flooding etc)
>and also because the turbines turn comparatively slowly meaning that they do
>not mince such things as seals, swimmers etc.
The energy in a flow of water is quite significant, even with very very
low head. Take a flow of 4kph = 1m/s and a rotor of 6m diam and you
intercept 30m^3/s. That is some 30T at 1m/s = 15kW. You might be able to
extract 30% of this to give you 5kW.
Hmm, forget I said that ....
Charles Francis
<stu...@zetnet.co.uk> writes
>The message <AXFjuYRm...@clef.demon.co.uk>
>from Charles Francis <cha...@clef.demon.co.uk> contains these words:
>> In message <200407292...@zetnet.co.uk>, Gerald L R Stubbs
>> <stu...@zetnet.co.uk> writes
>
>> >The cause of tides is the gravitational attraction of the moon and
>> >sun. There are spring tides when the moon and sun pull together
>> >or are diametrically oposite to one another, and neap tides when
>> >this is not the case.
>
>> Yes. All of that is right. But the two tides per day are due to the
>> elongation of the water in the direction of the moons pull. This
>> elongation rotates about the earth as the earth spins on its axis. So
>> the energy used/dissipated comes from the spinning of the earth.
>
>Right. I understand what you have said, and am going to think about
>it before replying. Apart from the earth's axial rotation, does not the
>moon also orbit the earth ?
Yes it does, in the same direction but much slower. As Oz pointed out
the angular momentum of the system has to be maintained, so as the spin
of the earth slows down the moon gets pushed into a higher obit.
Regards
--
Charles Francis
Charles Francis
>from Derek Moody <de...@farm-direct.co.uk> contains these words:
>
>> Tidal nodes lie in the places between those with large rise/fall. All that
>> water at high tide has to go somehwere - it all shunts along a bit and piles
>> up as high tide somewhere else before (mostly) coming back again (on a
>> looped route). Tidal nodes have little rise and fall but considerable tidal
>> streams. Iow tidal nodes are prime sites for tidal stream turbines.
>
>The Severn esturary has a mean difference between high an low tide of
>some thirty feet. This does not equate to the tidal difference of the
>sea that
>is west of the estuary, but is due to the shoaling and reduction in width of
>the estuary. This causes the flow of water to bunch-up, due to its
>momentum, and to achieve a higher level than that attained in the
>adjacent, open seas. Ideal place to situate a barrage.
Someone told me on one of the physics groups that in the absence of land
masses to stop the flow of water and cause it to bunch up, the tides
would be about 2" high.
Regards
--
Charles Francis
Tim Lamb
<de...@farm-direct.co.uk> writes
>>
>> to spot the principle proponents of the multiple thread and put up a
>> subject likely to test their intellect.
>
>But I wasn't in the DA thread...
Neither was the *nit nurse*:-)
It is a bit like trawling; you always get a proportion of non-target
species...
regards
--
Tim Lamb
Charles Francis
<o...@farmeroz.port995.com> writes
>Jim Webster <J...@zerospam.mok.net> writes
>>Because of the nature of the turbines, it isn't the head that is the factor
>>that makes the site interesting, but the fact that the tide is almost
>>constantly either coming in or going out and an awful lot of water flows
>>through them during the course of a day
>>Effectively they seem to be swapping quality (head) for quantity (width).
>>The reasons for this are they aren't allowed to meaningfully delay the
>>passage of the water (otherwise they could cause backing up/flooding etc)
>>and also because the turbines turn comparatively slowly meaning that they do
>>not mince such things as seals, swimmers etc.
>
>The energy in a flow of water is quite significant, even with very very
>low head. Take a flow of 4kph = 1m/s and a rotor of 6m diam and you
>intercept 30m^3/s. That is some 30T at 1m/s = 15kW. You might be able to
>extract 30% of this to give you 5kW.
>
>Hmm, forget I said that ....
>
remember any systems like this being touted at the centre for
alternative technology.
Or does it? The calculation is flawed. We are not taking 30T per sec and
stopping it from moving, extracting the energy in the process. Remember
we have lamina flow.. When you put in the turbine you are slowing the
flow of the entire stream. That's not 30T, but 30m^2 x length of the
flow, x density. Assume, for the sake of argument, that the turbine is
about 1km out and that 1km represents a meaningful approximation to the
amount of water slowed. Also that we only take 1/10th of its KE. Then
you get more like 500kW. How much does a windmill give you btw?
Regards
--
Charles Francis
Charles Francis
<o...@farmeroz.port995.com> writes
>Gerald L R Stubbs <stu...@zetnet.co.uk> writes
>>The message <WJNa6wC3...@farmeroz.port995.com>
>>from Oz <o...@farmeroz.port995.com> contains these words:
>>
>
>organ pipe this depends on the speed of waves in the sea and the
>distance between the shores.
>
>Now it not something I have delved deep into, rather I put my toe in,
>but tides also generate waves. When the high tide bumps into the states
>it can go no further and REFLECTS part of the energy. Now some deepwater
>wave can move surprisingly fast. Some of you may have seen the programs
>about earthquakes/landslips on one side of the pacific (ok big ones)
>moving long distances very quickly to give tidal waves on the other
>side.
>
>Much the same apparently happens in tides. So you have to make various
>second order allowances for tidal reflection to give the local result.
>
>That is, tides are far from 100% dissipative.
>
>The total energy in a tide is, however, pretty immense. Perhaps charles
>would like to estimate it for the world?
>
take me for. Some sort of computer? Also my database of useful numbers,
like the diameter of the world, regularly gets corrupted, like within
about 10 mins of looking it up. You do the calculation, and I'll tell
you if I think its right.
Regards
--
Charles Francis
Jim Webster
"Charles Francis" <cha...@clef.demon.co.uk> wrote in message
news:UjKmTTTe...@clef.demon.co.uk...
when the tide is going out it is several miles from the proposed site of the
barrier to the beach and even then you have two rivers feeding it.
When the tide is coming in you are talking about a stream that stretches
back many miles indeed
Jim Webster
Derek Moody
<URL:mailto:stu...@zetnet.co.uk> wrote:
> The message <b6ckg0lcrq0mkt0i6...@4ax.com>
> from sy...@despammed.com contains these words:
> > On Thu, 29 Jul 2004 20:21:51 +0100, Gerald L R Stubbs
> > <stu...@zetnet.co.uk> wrote:
> > There is a feedback path and it is related to mass only in that
> > momentum is conserved so there is an energy loss (friction/turbulence
> > effects). Energy is being transferred to the moon, it's velocity is
> > being increased and hence its orbit around the earth is increasing.
>
> Sorry, the above goes right over the top of my head. How is energy
> bieng transferred to the moon ?
See other post.
> What friction losses are you talking
> about ?
Moving water slowed by contact with the seabed, turbulence too.
> What do you mean when you say that the moon's orbit around the earth is
> increacing, do you mean that the moon's orbit is getting longer in time
> or that it is getting further away from the centre of the earth,
Both.
> and in
> either case what has this to do with tides ?
Distance reduces the scale of the tide. Slowing reduces the velocity.
Friction slows the Earth's rotation. Reducing scale, velocity and rotation
reduces the energy - all due to the feedback which reduces too.
> one of them. The amortisement of solar panels is still a very
> uninteresting propostion unless it is subject to some sort of subsidy,
Depends on the alternatives. We had a boat that was prone to lose battery
power in the winter as we were running at low revs for too high a proportion
night hours with heavy light usage. A pair of solar panels made all the
difference. Saved many times their cost in emergency battery charging.
Derek Moody
> from Derek Moody <de...@farm-direct.co.uk> contains these words:
> > Water has mass. The tidal bulge lags the moon, if delayed by obstructions
> > it will lag a little more and feedback its own gravity into the equation.
> > The apparent symmetry of the tidal bulge doesn't cancel btw as the
> > relationship is inverse square and not linear.
>
> Mathematics is not my subject, and I fear that your ultimate sentence,
> I am afraid, falls upon deaf ears, as I do not understand what you are
> saying.
It's easiest to illustrate as lamplight going through a window:
Assume a a square window at unit distance.
The curtains are lit by a quantity of light.
Open the curtains so the same quantity of light falls on the garden shed
which is as far away again. (If not move the shed 'til it is.)
The light spreads out to cover an area twice as wide and twice as high.
At double the distance the light covers four times the area (square) and is
spread out so it has only a quarter the brightness (inverse square).
Gravity works the same way. Three times the distance = one ninth the
strength (and so on.)
> Irrespective of that, I cannot see how a tidal bulge, effected by the
> gravitational effects of the sun and moon can have any reverse feed-back
> upon those two bodies as the mantle of water on the planet earth is only
> a part of the planet's mass, and it is the planet's total mass that is
> relevant in gravitational equations, and not their position.
IF spherical then the calculations can be done as points. The Earth isn't
quite a sphere, the tidal bulge exaggerates this, the nearer part of the
bulge has a disproportionally greater effect than the distant one (inverse
square).
The bulge is caused by this as well. The water on the far side is attracted
to the moon. The Earth itself, being slightly closer is attracted a little
more and the water on the near side is attracted most.
If you consider the rotaional(centrifugal) forces you will find they add to
the effect.
> If one cares to imagine a heavenly body that is shaped like a pork
> saussage, I would postulate that no matter what orientation it
> presented to other, nearby bodies, the gravitational equilibrium
> between those bodies would remain the same, as it is the total mass of
> a body, and not its shape that determines the gravitational equilibrium
> between them.
I only have a spicy beef chipolata to hand but what the hell?
Just as tides cause a bulge on both sides of the Earth anything that is
elongated will tend to line itself up pointing to the primary. Once it is
so aligned you can calculate as if all its mass were at it's centre of mass
- unless the tidal forces in an intense gravitational field become so great
they rip it in two. Hard to imagine? What if the object was all liquid
water? Now freeze it.
Derek Moody
> from Oz <o...@farmeroz.port995.com> contains these words:
>
> > predicting tide tables. So some of the wave motion is oscillatory and
> > thus non-dissipative.
>
> Tides may only be predicted in mean conditions. Predictions have
> historically been far exceeded due to the efffects of prolonged wind
> which
> have produced excessive tidal surges, such as the devastating spring tide
> that occurred some time in 1952 or thereabouts.
The tide remains the same but there is an additional quantity of water
blown/held in a bottleneck by the wind. Add the effect of a low barometer
and sea walls are breached.
Oz
>Gravity works the same way. Three times the distance = one ninth the
>strength (and so on.)
Tides, of course, work on a cube law......
Oz
>Someone told me on one of the physics groups that in the absence of land masses
>to stop the flow of water and cause it to bunch up, the tides would be about 2"
>high.
Its not hard to work it out, its in every old A level physics book.
IIRC circa 500mm, not 50.
Oz
>Or does it? The calculation is flawed. We are not taking 30T per sec and
>stopping it from moving, extracting the energy in the process. Remember we have
>lamina flow.. When you put in the turbine you are slowing the flow of the entire
>stream. That's not 30T, but 30m^2 x length of the flow, x density. Assume, for
>the sake of argument, that the turbine is about 1km out and that 1km represents
>a meaningful approximation to the amount of water slowed. Also that we only take
>1/10th of its KE. Then you get more like 500kW. How much does a windmill give
>you btw?
<sigh>
1m length PER SECOND. 'Cos the result is in watts.
Obviously it doesn't quite work as I described (hence the 30% bit)
because otherwise you will end up with a big heap of water next to your
turbine.
What actually happens is the stuff that doesn't go in, goes round, and
speeds up the slowed stuff some distance downstream.
Oz
>when the tide is going out it is several miles from the proposed site of the
>barrier to the beach and even then you have two rivers feeding it.
>When the tide is coming in you are talking about a stream that stretches
>back many miles indeed
Most tidal barrages do a variant of
tide goes up, fills a reservoir.
Tide goes down, empty reservoir through turbines.
Oz
>My god, that would be a (hushed tone) numerical calculation. What do you take me
>for. Some sort of computer? Also my database of useful numbers, like the
>diameter of the world, regularly gets corrupted, like within about 10 mins of
>looking it up. You do the calculation, and I'll tell you if I think its right.
Tad busy right now.
Harvest, don't you know...?
Jim Webster
"Oz" <o...@farmeroz.port995.com> wrote in message
news:0Dhy4rPDMjDBFwR$@farmeroz.port995.com...
> Jim Webster <J...@zerospam.mok.net> writes
> >when the tide is going out it is several miles from the proposed site of
the
> >barrier to the beach and even then you have two rivers feeding it.
> >When the tide is coming in you are talking about a stream that stretches
> >back many miles indeed
>
> Most tidal barrages do a variant of
> tide goes up, fills a reservoir.
> Tide goes down, empty reservoir through turbines.
they are very careful to not describe this as a barrage and do not use the
term reservoir, they try to give the impression that they barely slow the
water and obviously have no environmental effects whatsoever
Purely a PR approach
Jim Webster
Michelle Fulton
>
> Not hard to imagine, because again, I fear, I do not understand
> what you are talking about.
LOL :-)
Hi, Stubbsy :-)
I was reading along, straining my brain to try to comprehend this stuff, all
serious, then you blindside me with the above statement! Good thing there
wasn't food or drink in my mouth, because it would have ended up on the
monitor :-)
--
Michelle
Fort Worth, Texas, USA
Life is short. Be determined to enjoy every minute of it :-)
Oz
Separately also posted to uba, as spr moderators are all on holiday and
a reply is likely to be slow.
When x-posting to spr, please keep posts short, clear and absolutely on
topic. Moderators are busy and unpaid.
[Posted to sci.physics.research AND uk.business.agriculture]
[Could any technical posters note the level of explanation likely to be
required for a fairly non-technical crosspost.]
Gerald L R Stubbs <stu...@zetnet.co.uk> writes
>Is that not exactly what I was postulating? That whatever the state of
>the tides, worldwide, it is the centre of gravity of the earth that
>exerts an
>influence on other heavenly bodies, or to put it another way, it is
>the total
>mass of the earth that exerts influence, which is not related to the shape
>of the earth from day to day.
OK, stubbsy, I have a go.
I will take the sun and the earth, dispensing with the moon which we
remove for the sake of simplicity.
The earth sun system is balanced. That is the CENTRE of the earth feels
no acceleration just like an orbiting spaceman. This is because gravity
is precisely strong enough to exactly balance the centrifugal force.
Note that centrifugal force is a fictitious force that we have to bring
in if we are to force something into a circular orbit. Its only seen by
bodies forced into a circular orbit, in this case by gravity. Since
gravity acts on every particle of our bodies, no net force is seen,
which is why astronauts in orbit feel neither gravitational nor
centrifugal forces despite travelling in a circular path.
Now, crudely, the bit of the earth on the surface facing the sun is
closer than the centre. Its thus imbalanced. It feels a stronger
attraction than the centre and so tries to fall in towards the sun.
Equally the far side of the earth is further away, and feels a lesser
pull from the sun and so tries to fly away from the sun.
There is a similar effect for the centrifugal force, acting in the SAME
direction. That is the tighter orbit inside is going too slowly and
wants to drop to a lower orbit and vice-versa for the far side.
This is all symmetrical, so you get symmetrical tides.
The height of the tide turns out to depend on the cube of the sun-earth
distance.
Now lets think what happens if the tides (rotating once in 24 hours) get
slowed by continents. Well, its just like a pair of brake shoes, slowing
the earth's rotation. The sunward tide, which is water trying to orbit
slower than the earth rotates, is 'behind itself'. Instead of being
exactly facing the sun its a bit round the side. The force is thus ever
so slightly unbalanced and doesn't quite point directly along the sun-
earth axis. There is thus a small resultant force pushing the earth
along the orbital direction, changing its orbital speed and thus
altering its orbital distance.
I've never actually done this calculation, so I don't know if rotation
one way will push the orbit away, and the other direction pulling it in.
I'm not about to work it out, one hires astrophysicists for this. My
guess is that the direction matters.
Note that the earth pulls tides from the sun, so there is an effect on
the sun, from the earth and the tides on the earth.
Oz
>> but tides also generate waves. When the high tide bumps into the states
>> it can go no further and REFLECTS part of the energy. Now some deepwater
>> wave can move surprisingly fast. Some of you may have seen the programs
>> about earthquakes/landslips on one side of the pacific (ok big ones)
>> moving long distances very quickly to give tidal waves on the other
>> side.
>
>Ninglish. Funny things, in the sense of being curious, as they
>produce little
>wave effect on the surface of the sea. They are not, as the popular
>imagination supposes, giant surface waves, but giant subsea waves that
>travel at the most amazing speeds, some one hundred miles an hour, I
>seem to remember.
I think faster.
>When they hit costal shelving their momentum allows them to go far
>inland, so long as the grade of the land is not too severe.
>
>> Much the same apparently happens in tides. So you have to make various
>> second order allowances for tidal reflection to give the local result.
>
>Tides may be predicted years in advance, weather can only be safely
>predicted on a very short forcast, one to three hours normally, except
>in very stable atmospheric conditions, which conditions do not normally
>prevail over the UK.
>Thus the second order allowances of which you speak is short-order stuff.
No, it happens every day. Each tide producing waves that bounce all over
the oceans in a predictable manner. So a very high tide today in england
will affect the tide a day or so later in america, and vice-versa. OK,
its only a small effect, but its one reason for the irregularity of tide
heights. There are also more local effects in smaller oceans/seas.
You can't expect to slosh gigatons of water about and not make big
waves.
Oz
[Could any technical posters note the level of explanation likely to be
required for a fairly non-technical crosspost.]
Gerald L R Stubbs <stu...@zetnet.co.uk> writes
--
Charles Francis
<o...@farmeroz.port995.com> writes
>Charles Francis <cha...@clef.demon.co.uk> writes
>>Someone told me on one of the physics groups that in the absence of
>>land masses
>>to stop the flow of water and cause it to bunch up, the tides would be
>>about 2"
>>high.
>
>Its not hard to work it out,
But that requires that I pick up a pen and paper!
> its in every old A level physics book.
I threw mine away when I found they had too many out of date
definitions.
>
>IIRC circa 500mm, not 50.
>
Regards
--
Charles Francis
Charles Francis
<o...@farmeroz.port995.com> writes
>Charles Francis <cha...@clef.demon.co.uk> writes
>
>>Or does it? The calculation is flawed. We are not taking 30T per sec and
>>stopping it from moving, extracting the energy in the process.
>>Remember we have
>>lamina flow.. When you put in the turbine you are slowing the flow of
>>the entire
>>stream. That's not 30T, but 30m^2 x length of the flow, x density.
>>Assume, for
>>the sake of argument, that the turbine is about 1km out and that 1km
>>represents
>>a meaningful approximation to the amount of water slowed. Also that we
>>only take
>>1/10th of its KE. Then you get more like 500kW. How much does a windmill give
>>you btw?
>
><sigh>
>
>1m length PER SECOND. 'Cos the result is in watts.
>
>Obviously it doesn't quite work as I described (hence the 30% bit)
>because otherwise you will end up with a big heap of water next to your
>turbine.
>
>What actually happens is the stuff that doesn't go in, goes round, and
>speeds up the slowed stuff some distance downstream.
>
one would need some sort of barrage to get the water to pass through the
turbines.
Regards
--
Charles Francis
David G. Bell
<CUOPN8Bg...@farmeroz.port995.com>
o...@farmeroz.port995.com "Oz" wrote:
> No, it happens every day. Each tide producing waves that bounce all over
> the oceans in a predictable manner. So a very high tide today in england
> will affect the tide a day or so later in america, and vice-versa. OK,
> its only a small effect, but its one reason for the irregularity of tide
> heights. There are also more local effects in smaller oceans/seas.
>
> You can't expect to slosh gigatons of water about and not make big
> waves.
Gallileo tried to predict tides in the Adriatic, and worked on the idea
of water sloshing in a tub. Partly because the Adriatic is small,
aligned north-south, and nearly independent of the Mediterranean, it's
actually a pretty good model. The lunar and solar tides do have some
effect, but they're at the wrong frequncy to pump the system.
--
David G. Bell -- SF Fan, Filker, and Punslinger.
"History shows that the Singularity started when Sir Tim Berners-Lee
was bitten by a radioactive spider."
Oz
>Quite. A single turbine wouldn't be brilliantly efficient. I would think one
>would need some sort of barrage to get the water to pass through the turbines.
I think you mean effective rather than efficient.
Of course one can channel the water to increase the velocity, which
gains you output per turbine in a square relationship. Trouble is its
hard to get seaflows much more than about 10mph.
Which is, of course, why people tend to barrages....
Steve Rawlings. www.dexterbeef.co.uk
L R Stubbs) wrote:
> The Severn Barrage should have been built thirty years ago. It is
> probably too late
> to undertake now, as minority opinion, which is worried about birdies,
> would probably swing public opinion against the scheme.
Oil at $80/barrel may make us forget the birdies...
Steve Rawlings
--
Charles Francis
<stu...@zetnet.co.uk> writes
>> If you consider the rotaional(centrifugal) forces you will find they add to
>> the effect.
>
>Shit! I have learned that there is no such thing as centrifugal
>force.... Have I been wrongly informed?
>
Oh good. A purely abstract theoretical question. One which I can do. No
orrible numbers at all.
The short answer is yes. When treated correctly there is a centrifugal
force. It has merely been banned from school syllabuses owing to the
fact of so many schoolboy mistakes with it. What this really means is
there is no such thing as centrifugal force on the school exam syllabus.
To understand centrifugal, and the lesser known coriolis, force you have
to think of a rotating reference frame. If you are watching children on
a playground roundabout you are in a non-rotating frame (ignoring
earth's motions). In this case there is no centrifugal force. You
describe the motion of the children by saying that they are always being
pulled inwards (we hope, or they will fall off) and accelerating towards
the centre of the roundabout.
But if you get onto the roundabout yourself you will be in a rotating
reference frame. You will now feel a force pulling you outwards from the
centre of the roundabout. This is the centrifugal force. If you move you
will feel a force pushing you sideways to the motion. This is the
coriolis force. The Coriolis force is responsible for the fact that air
flows around the earth do not go straight from high to low pressure, but
almost at right angles, along the isobars, and for the direction water
(usually) goes down the plug hole.
Notice that for both the centrifugal force and the Coriolis force the
force acts on every part of your body, rather like gravity. In
Einstein's theory of general relativity gravity also becomes one of
these "fictional" forces which arise from the choice of reference frame.
As I am sitting here the "real" forces acting on me come from the floor
and the chair. This is because I am using an accelerating reference
frame - which means accelerating relative to free fall. If you use a
reference frame in free fall (the falling lift is the classical example)
then there is no force of gravity.
Regards
--
Charles Francis
Oz
>Notice that for both the centrifugal force and the Coriolis force the force acts
>on every part of your body, rather like gravity. In Einstein's theory of general
>relativity gravity also becomes one of these "fictional" forces which arise from
>the choice of reference frame. As I am sitting here the "real" forces acting on
>me come from the floor and the chair. This is because I am using an accelerating
>reference frame - which means accelerating relative to free fall. If you use a
>reference frame in free fall (the falling lift is the classical example) then
>there is no force of gravity.
Yup, when falling you don't feel a thing, until you hit the bottom....
This is why pure drop rides are tame. A brief period whilst your body
contents rearrange themselves in zero-g, then nothing.
Those rides with variable acceleration, OTOH, can be 'rather nasty'.