Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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On Thu, 19 Apr 2018 17:09:23 -0700 (PDT), wrote:

...I also agree with Jeff Leiberman's caveat


Argh. It's Jeff Liebermann. Spell my name correctly or I shall call
upon the gods for divine retaliation. Heed this first and last
warning lest the wrath of the gods fall upon thy house, when darkness
shall envelope thy LCD monitor, and a plague of bugs infest the
software by which you have taken my name in vain.

I've been hearing of laptops with mo fan, and of course smartphones
don't have them.


Most of my Chromebooks do not have a fan. Heat is conducted from the
CPU to either a metal case or the metal shield on the bottom of the
keyboard.

Will it eventually get to the point where they don't
need heatsinks ?


Methinks not. For every decrease in CPU power consumption, there is
an equal and opposite increase in clock speeds. The result is that
the maximum power remains about the same or slightly lower. However,
when the CPU is at idle and not active, the power consumption is much
lower.

Get an efficient enough switch and it could happen. I have already
seen power switching transistors with no heat sink except the tab
itself.
At 0 Vcesat, 0 Vceo, 0 Vbe, 0 tOFF and 0 tON there is no heat to sink.


There's also no signal. Might be an IGBT FET. Very low Vce(sat) at
high currents. However, it's not zero, so there's still some heat
that needs to removed.

--
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150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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"Argh. It's Jeff Liebermann. Spell my name correctly or I shall call upon the gods for divine retaliation. "

So you're the pagan sorcerer responsible for my internet outage of a few hours today.

"Most of my Chromebooks do not have a fan. Heat is conducted from the CPU to either a metal case or the metal..."


Something that is not plastic ? Isn't there some law against that ?

"For every decrease in CPU power consumption, there is

an equal and opposite increase in clock speeds."

I stopped all attempts at overclocking in the Pentium 2 days, but I grasp the concept. However, from what I have gleaned the processor speed is not the end of the world usually. In a PC for example the RAM is slower, the HD slower than that, and so on until we get to the speed of access to data sources, i.e. the internet. So conceivably couldn't they just not crank the clock to the max and save power and generate less heat ? Or do they already do that ? My laptops have a setting, performance, balanced and battery life. Is that possibly an indirect "underclocking" control ? If not, what is it ?

"Might be an IGBT FET. Very low Vce(sat) at

high currents. However, it's not zero, so there's still some heat
that needs to removed. "

The current should not be that high, all that current is cumulative right ? Seems like the main issue is charging and discharging the input capacitance. As such,lower clock speeds should be quite effective. If they could get it down to the point where no heatsink is needed at all, wouldn't there be enough advantage in cost to justify a slightly lower clock speed ? A phone accessing the internet for example, how much does that clock speed really mean then ? I am not being sarcastic here, that is a valid question, (I think) how processor intensive is all this ?

Maybe there is advertising value. I could see the yuppies in the cellphone store looking at specs and saying "LOOK, this one has a higher clock speed !".

Or are these the issues that keep the engineers up at night ?
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Jeff Liebermann wrote:
On Fri, 13 Apr 2018 09:28:28 -0700, wrote:

On Thu, 12 Apr 2018 13:31:11 -0700, Jeff Liebermann
wrote:

On Thu, 12 Apr 2018 11:59:48 -0700,
wrote:

I use some very fine particle size diamond lapping compounds in my
shop.

What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards. The bulk of the heat is passed by metal to
metal contact.


Smallest grain size is 1 micron. Or .0000039 Inches


or 39 micro inches (one too many zeros).

My best surface plate is flat within 30 millionths of an
inch. My best set of gauge blocks, the ceramic ones, are +1 to + 3
millionths in size except for the 4 inch block which is +4 millionths.


Arctic Silver 5 uses:
http://www.arcticsilver.com/as5.htm
Average Particle Size: 0.49 micron or 0.000020 inch or 20 micro
inch. However, they use:
"Arctic Silver 5 uses three unique shapes and sizes of
pure silver particles to maximize particle-to-particle
contact area and thermal transfer."

Crystalline diamond nanoparticles have an advantage, where the flat
facet surfaces provide better thermal conduction than random, rough,
or spherical shapes.
https://www.google.com/search?q=diamond+nanoparticles&tbm=isch

Your diamond particles are twice the diameter, but considering the mix
of sizes in Arctic Silver 5, the sizes are comparable. They should
work if you decide to mix your own thermal goo. However, you can buy
diamond thermal paste:
https://www.innovationcooling.com/products/ic-diamond/
The data sheet claims:
Average Particle Size: 40 µ maximum particle diameter
40 micro what? inches or meters? Probably inches which is the same
as your lapping compound.

If we made CPU's and heat sinks with the same precision as your gauge
blocks, then we wouldn't need thermal paste or even mounting hardware.
The two surfaces would stick together by themselves.


I think the screw down components can warp under torqueing, but flat seems
good to try and achieve. I noticed some power modules were not perfectly
flat, and I started to sand them on a flat precision table. They were
pretty far off from flat.


Greg
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On Friday, 20 April 2018 06:09:03 UTC+1, wrote:

"For every decrease in CPU power consumption, there is

an equal and opposite increase in clock speeds."

I stopped all attempts at overclocking in the Pentium 2 days, but I grasp the concept. However, from what I have gleaned the processor speed is not the end of the world usually. In a PC for example the RAM is slower, the HD slower than that, and so on until we get to the speed of access to data sources, i.e. the internet.


OTOH the CPU does a lot more than the others. Sometimes cpu is the limiting factor, sometimes not. IMLE with clocking it did make a significant difference. I don't bother clocking now, but once it was a deal maker.

So conceivably couldn't they just not crank the clock to the max and save power and generate less heat ? Or do they already do that ?


that's done nearly all the time. It's one reason why most CPUs are clockable.

My laptops have a setting, performance, balanced and battery life. Is that possibly an indirect "underclocking" control ? If not, what is it ?


probably. It also affects HDD power down settings on HDD equipped laptops.

"Might be an IGBT FET. Very low Vce(sat) at

high currents. However, it's not zero, so there's still some heat
that needs to removed. "

The current should not be that high, all that current is cumulative right ? Seems like the main issue is charging and discharging the input capacitance. As such,lower clock speeds should be quite effective.


There's capacitance everywhere that gets charged & discharged each time it changes between 0 & 1. There's also that conduction overlap time when something changes state.

If they could get it down to the point where no heatsink is needed at all, wouldn't there be enough advantage in cost to justify a slightly lower clock speed ?


you need a huge speed reduction to go heatsinkless.

A phone accessing the internet for example, how much does that clock speed really mean then ? I am not being sarcastic here, that is a valid question, (I think) how processor intensive is all this ?


Modern net browsers are real cpu hogs


Maybe there is advertising value. I could see the yuppies in the cellphone store looking at specs and saying "LOOK, this one has a higher clock speed !".

Or are these the issues that keep the engineers up at night ?


As more & more gets squeezed into a cpu, power use per flop has to fall dramatically. There is no other way. The future lies with very low power gates relative to today.


NT
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In article ,
wrote:

So conceivably couldn't they just not crank the clock to the max and save power and generate less heat ? Or
do they already do that ? My laptops have a setting, performance, balanced and battery life. Is that possibly an indirect "underclocking"
control ? If not, what is it ?


Yes, almost certainly it is just that (and perhaps more as well).

Most modern CPUs/motherboards/chipsets support multiple CPU clock
rates - the CPU's own internal clock signal is created via a
PLL/multiplier system, based on a slower fixed-rate crystal clock.
The multiplier system is under processor control, so it's possible for
the CPU to switch speeds "on the fly" (with a momentary pause while
the PLL re-locks). I believe this is usually managed via the ACPI
layer in the BIOS/UEFI.

At the higher (user-visible) layer, this is usually set up via a
performance setting of the sort you mention. The setting then
controls a set of policies managed by the operating system, which
specify when to change CPU clock speeds (and sometimes voltages as
well) based on your usage patterns.

"Battery life" would probably lock the speed at the lowest supported
value, or at least to range of the slower values. "Performance" might
lock it to the highest speed at all times. "Balanced" would either be
a fixed speed in the middle of the range, or a dynamic system which
increases the CPU speed in increments when the CPU is mostly busy, and
reduces it when the CPU is idle more than a certain fraction of the
time.

On the Linux laptop I use, I have a choice of several such dynamic
policies... some are more aggressive about increasing CPU speed, some
are more conservative. The CPU speed can be varied over a range of
about 2:1, on a per-core basis (and a core which is currently sitting
idle isn't using much current at any clock speed, although consumption
is less at the lower clock speeds even when idle).

The current should not be that high, all that current is cumulative right ? Seems like the main issue is charging and discharging the input
capacitance. As such,lower clock speeds should be quite effective. If they could get it down to the point where no heatsink is needed at all,
wouldn't there be enough advantage in cost to justify a slightly lower clock speed ? A phone accessing the internet for example, how much does
that clock speed really mean then ? I am not being sarcastic here, that is a valid question, (I think) how processor intensive is all this ?


Depends what you're doing. Just downloading a file is probably not
CPU-expensive. Rendering a web page full of fancy animated graphics
and video, considerably more so. Doing full-screen video may require
little from the CPU, but may push the GPU quite hard (MPEG-4 or
similar video decoding).

Phones _tend_ to be designed to optimize battery life, as this is a
key selling point... and so they'll be somewhat more conservative
about speeding up their CPUs.

And, phones do have heatsinks. They're called "hands" :-)








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On Fri, 20 Apr 2018 07:37:13 -0000 (UTC), gregz
wrote:

I think the screw down components can warp under torqueing, but flat seems
good to try and achieve. I noticed some power modules were not perfectly
flat, and I started to sand them on a flat precision table. They were
pretty far off from flat.


Nope. They might be warped on arrival, but are impossible to
straighten without sanding or milling.

Back in about 1976, we were having flatness problems with the
transistors used in a linear power supply. There was a large extruded
aluminum heat sink, and either 4 or 8 2N3055 transistors in TO3
packages. The heat sink was milled and quite flat, but the TO3
packages were warped from what I would guess was a worn stamping die.
Some clever person in production decided that the cases could be
straightened most easily by simply tightening the 6-32 screws holding
the devices to the heat sink. After crushing the nylon shoulder
washer, he torqued the hell out of the screw until the head broke off,
and then gave up. The uneven squashing of the silpad insulator showed
that the case was still warped.

At that point, someone in production decided that I needed some unpaid
overtime. It was now my project, errr... headache. I put together a
dial indicator and verified that no amount of pressure from 6-32
mounting screws is going to bend the TO3 base when the spot welded lid
was acting as a stiffener. Using a strain gauge, a bar of steel, and
brute force, I determined that the best I can do with trying to
straighten the TO3 packages was to bend ears near the mounting holes,
making the flatness problem even worse. I fixed a few packages by
milling the bottom of the package, but the cost was too high. Cheaper
just to buy new transistors from a different vendor that weren't
warped.

The only good thing to come out of this waste of time was a fixture
that I threw together to measure the flatness of the TO3 and later RF
power transistor packages. It saved having the same problem repeat
itself in later years.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Once upon a time on usenet wrote:
"In my opinion you should never 'squeeze' it tighter than the clip /
fastener is going to hold it. Otherwise you squeeze too much out and
are left with voids. "


Disagree. What seem like voids are either the points of actual metal
to metal contact or so close that you can't see the compound.
Remember I said a bead or daub, if it is spread it is almost for sure
not even and that will cause actual voids where it traps the air at
the low spots of the compound. Some of those clips are too weak to
overcome the viscosity of the compound, and some of that aluminum
stuff they make the heatsinks out of is very soft and the screws
might strip. The main thing is not to let it come up or move. If it
is done right they are usually stuck pretty good though.


I've pressed very hard on some components, watched the compound come out all
around then, on relasing the pressure to 'fastener pressure' have seen some
of the ooze suck back in and sometmes air suck back in. Granted these
weren't on ideal surfaces but since then, on those types of interfaces I let
the fastener do the squeezing.

"I've done a lot of work on laptops, a lot of them nasty to get into
so it's best to do it right first time."


Agreed, with anything. It's been said "How come there is never enough
time to do it right but always enough time to to it again". I have
even told people now and then "Hell no I don't want to do it right, I
just don't want to do it again". I also don't want the liability, if
the part fails guess what ?

"I've also lapped more than my share of CPU

'spreaders' (IHSs) and (desktop machine) heatsink bases. "

I haven't done that many processors in PCs, I just follow
instructions. I did much work in power supplies and amps,
unfortunately lapping is simply impossible on most. I also agree with
Jeff Leiberman's caveat about making the surface concave. If you do
that it could be worse than not lapping at all.


I have variously sized bits of glass that I use as backing for the wet'n'dry
sandpaper that I use to ensure relative flatness. The glass isn't as flat as
gauge blocks but it's sufficient.

I only lapped in some
output ICs once actually. I was extremely low on compound so I
thinned out what was leftover and lapped with it. The ICs required no
insulator being a totally plastic package. At the end of the lapping
I had them in position and moved no more so that if there were any
larger particles in there they would stay put, embedded and not keep
the surfaces away. The only reason I was even able was because I was
retrofitting a pair of LM3886 in place of a big STK and made a clip
that went from one mounting screw to the other. I had plenty of room.
(I would have put i pre outs and had the guy use an external power
amp but the damn tone controls were in the global feedback loop)

Luckily I don't have to do much of that anymore or I would have a
caulking gun full of compound like this one place I worked. Makes it
easier to apply and I would never run out. They did but it took years
even with a bunch of techs working.


For laptops, desktops and critcal ICs I use Arctic Silver. I bought a 'PC
builders' size syringe of it. For less critical stuff I use either
Electrolube HTC or, for 'cheap jobs' that need a lot of it and have large
contact areas / raditaors (mostly aluminium LED PCBs to heatsinks), stuff I
get from AliExpress.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

I've been hearing of laptops with mo fan, and of course smartphones
don't have them. Will it eventually get to the point where they don't
need heatsinks ? Get an efficient enough switch and it could happen.
I have already seen power switching transistors with no heat sink
except the tab itself.

At 0 Vcesat, 0 Vceo, 0 Vbe, 0 tOFF and 0 tON there is no heat to sink.




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On Sat, 21 Apr 2018 15:13:02 +1200, "~misfit~"
wrote:

Once upon a time on usenet wrote:
"In my opinion you should never 'squeeze' it tighter than the clip /
fastener is going to hold it. Otherwise you squeeze too much out and
are left with voids. "


Disagree. What seem like voids are either the points of actual metal
to metal contact or so close that you can't see the compound.
Remember I said a bead or daub, if it is spread it is almost for sure
not even and that will cause actual voids where it traps the air at
the low spots of the compound. Some of those clips are too weak to
overcome the viscosity of the compound, and some of that aluminum
stuff they make the heatsinks out of is very soft and the screws
might strip. The main thing is not to let it come up or move. If it
is done right they are usually stuck pretty good though.


I've pressed very hard on some components, watched the compound come out all
around then, on relasing the pressure to 'fastener pressure' have seen some
of the ooze suck back in and sometmes air suck back in. Granted these
weren't on ideal surfaces but since then, on those types of interfaces I let
the fastener do the squeezing.

"I've done a lot of work on laptops, a lot of them nasty to get into
so it's best to do it right first time."


Agreed, with anything. It's been said "How come there is never enough
time to do it right but always enough time to to it again". I have
even told people now and then "Hell no I don't want to do it right, I
just don't want to do it again". I also don't want the liability, if
the part fails guess what ?

"I've also lapped more than my share of CPU

'spreaders' (IHSs) and (desktop machine) heatsink bases. "

I haven't done that many processors in PCs, I just follow
instructions. I did much work in power supplies and amps,
unfortunately lapping is simply impossible on most. I also agree with
Jeff Leiberman's caveat about making the surface concave. If you do
that it could be worse than not lapping at all.


I have variously sized bits of glass that I use as backing for the wet'n'dry
sandpaper that I use to ensure relative flatness. The glass isn't as flat as
gauge blocks but it's sufficient.

I only lapped in some
output ICs once actually. I was extremely low on compound so I
thinned out what was leftover and lapped with it. The ICs required no
insulator being a totally plastic package. At the end of the lapping
I had them in position and moved no more so that if there were any
larger particles in there they would stay put, embedded and not keep
the surfaces away. The only reason I was even able was because I was
retrofitting a pair of LM3886 in place of a big STK and made a clip
that went from one mounting screw to the other. I had plenty of room.
(I would have put i pre outs and had the guy use an external power
amp but the damn tone controls were in the global feedback loop)

Luckily I don't have to do much of that anymore or I would have a
caulking gun full of compound like this one place I worked. Makes it
easier to apply and I would never run out. They did but it took years
even with a bunch of techs working.


For laptops, desktops and critcal ICs I use Arctic Silver. I bought a 'PC
builders' size syringe of it. For less critical stuff I use either
Electrolube HTC or, for 'cheap jobs' that need a lot of it and have large
contact areas / raditaors (mostly aluminium LED PCBs to heatsinks), stuff I
get from AliExpress.

The reason the glass is so flat is because it is floated on molten tin
in order to flatten it. So it should match the curvature of the earth.
Though not flat enough to use as a surface plate for much of the
inspection work I do it is still very flat and plenty good enough to
use with wetordry paper to flatten stuff like the sealing surfaces for
air compressor reed valves.
Eric


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On 4/21/2018 10:31 AM, wrote:
On Sat, 21 Apr 2018 15:13:02 +1200, "~misfit~"
wrote:

Once upon a time on usenet
wrote:
"In my opinion you should never 'squeeze' it tighter than the clip /
fastener is going to hold it. Otherwise you squeeze too much out and
are left with voids. "

Disagree. What seem like voids are either the points of actual metal
to metal contact or so close that you can't see the compound.
Remember I said a bead or daub, if it is spread it is almost for sure
not even and that will cause actual voids where it traps the air at
the low spots of the compound. Some of those clips are too weak to
overcome the viscosity of the compound, and some of that aluminum
stuff they make the heatsinks out of is very soft and the screws
might strip. The main thing is not to let it come up or move. If it
is done right they are usually stuck pretty good though.


I've pressed very hard on some components, watched the compound come out all
around then, on relasing the pressure to 'fastener pressure' have seen some
of the ooze suck back in and sometmes air suck back in. Granted these
weren't on ideal surfaces but since then, on those types of interfaces I let
the fastener do the squeezing.

"I've done a lot of work on laptops, a lot of them nasty to get into
so it's best to do it right first time."

Agreed, with anything. It's been said "How come there is never enough
time to do it right but always enough time to to it again". I have
even told people now and then "Hell no I don't want to do it right, I
just don't want to do it again". I also don't want the liability, if
the part fails guess what ?

"I've also lapped more than my share of CPU
'spreaders' (IHSs) and (desktop machine) heatsink bases. "

I haven't done that many processors in PCs, I just follow
instructions. I did much work in power supplies and amps,
unfortunately lapping is simply impossible on most. I also agree with
Jeff Leiberman's caveat about making the surface concave. If you do
that it could be worse than not lapping at all.


I have variously sized bits of glass that I use as backing for the wet'n'dry
sandpaper that I use to ensure relative flatness. The glass isn't as flat as
gauge blocks but it's sufficient.

I only lapped in some
output ICs once actually. I was extremely low on compound so I
thinned out what was leftover and lapped with it. The ICs required no
insulator being a totally plastic package. At the end of the lapping
I had them in position and moved no more so that if there were any
larger particles in there they would stay put, embedded and not keep
the surfaces away. The only reason I was even able was because I was
retrofitting a pair of LM3886 in place of a big STK and made a clip
that went from one mounting screw to the other. I had plenty of room.
(I would have put i pre outs and had the guy use an external power
amp but the damn tone controls were in the global feedback loop)

Luckily I don't have to do much of that anymore or I would have a
caulking gun full of compound like this one place I worked. Makes it
easier to apply and I would never run out. They did but it took years
even with a bunch of techs working.


For laptops, desktops and critcal ICs I use Arctic Silver. I bought a 'PC
builders' size syringe of it. For less critical stuff I use either
Electrolube HTC or, for 'cheap jobs' that need a lot of it and have large
contact areas / raditaors (mostly aluminium LED PCBs to heatsinks), stuff I
get from AliExpress.

The reason the glass is so flat is because it is floated on molten tin
in order to flatten it. So it should match the curvature of the earth.
Though not flat enough to use as a surface plate for much of the
inspection work I do it is still very flat and plenty good enough to
use with wetordry paper to flatten stuff like the sealing surfaces for
air compressor reed valves.
Eric


Interesting. I remember reading that ocean water is higher near
underwater mountain tops due to increased gravitational attraction and
measurable from satellites, I wonder if tanks could be designed with
non-flat bottoms to counteract what you mentioned.




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"Interesting. I remember reading that ocean water is higher near
underwater mountain tops due to increased gravitational attraction and
measurable from satellites,"

The would be one hell of a dense mountain to do that, I would think it more likely to be because of a decreased gravitational pull being forced away from the center of mass of the planet, due to its inverse square relationship. But that is not my field of expertise. (is anything ? the more I learn the less I know, if it weren't for learning from mistakes I would be a babbling idiot - NO COMMENTS FROM THE PEANUT GALLERY HERE !)

"I wonder if tanks could be designed with non-flat bottoms to counteract what you mentioned"


Pretty sure that would not work because gravity is the leveling force. As such the shape of the bottom should not matter.

Perhaps at a high altitude with a very large mass (dense, not voluminous) placed under the center of the tank it could be compensated. But then that makes splitting hairs look like hitting the broad side of a barn with a planet.
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Actually, maybe a half spherical or hyperbolic shaped tank bottom would work. However that would take a hell of alot of tin.
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On 4/21/2018 5:19 PM, wrote:
"Interesting. I remember reading that ocean water is higher near

underwater mountain tops due to increased gravitational attraction and
measurable from satellites,"

The would be one hell of a dense mountain to do that, I would think it more likely to be because of a decreased gravitational pull being forced away from the center of mass of the planet, due to its inverse square relationship. But that is not my field of expertise. (is anything ? the more I learn the less I know, if it weren't for learning from mistakes I would be a babbling idiot - NO COMMENTS FROM THE PEANUT GALLERY HERE !)

"I wonder if tanks could be designed with non-flat bottoms to counteract what you mentioned"


Pretty sure that would not work because gravity is the leveling force. As such the shape of the bottom should not matter.

Perhaps at a high altitude with a very large mass (dense, not voluminous) placed under the center of the tank it could be compensated. But then that makes splitting hairs look like hitting the broad side of a barn with a planet.


I don't know the correct physics, just read a bit...

Satellite observations
The alternative is an indirect method that uses satellites fitted with
radar altimeters.
These spacecraft can infer the shape of the ocean bottom from the shape
of the water surface above.
Because water follows gravity, it is pulled into highs above the mass of
tall seamounts, and slumps into depressions over deep trenches.
http://www.bbc.com/news/science-environment-29465446

The Hidden Earth: Undersea Mountains by the Thousands
http://www.slate.com/blogs/bad_astro...satellite.html




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On 22/04/18 10:46, Mike S wrote:
On 4/21/2018 5:19 PM, wrote:
"Interesting. I remember reading that ocean water is higher near

underwater mountain tops due to increased gravitational attraction and
measurable from satellites,"

The would be one hell of a dense mountain to do that, I would think it
more likely to be because of a decreased gravitational pull being
forced away from the center of mass of the planet, due to its inverse
square relationship. But that is not my field of expertise. (is
anything ? the more I learn the less I know, if it weren't for
learning from mistakes I would be a babbling idiot - NO COMMENTS FROM
THE PEANUT GALLERY HERE !)

"I wonder if tanks could be designed with non-flat bottoms to
counteract what you mentioned"


Pretty sure that would not work because gravity is the leveling force.
As such the shape of the bottom should not matter.

Perhaps at a high altitude with a very large mass (dense, not
voluminous) placed under the center of the tank it could be
compensated. But then that makes splitting hairs look like hitting the
broad side of a barn with a planet.


I don't know the correct physics, just read a bit...

Satellite observations
The alternative is an indirect method that uses satellites fitted with
radar altimeters.
These spacecraft can infer the shape of the ocean bottom from the shape
of the water surface above.
Because water follows gravity, it is pulled into highs above the mass of
tall seamounts, and slumps into depressions over deep trenches.
http://www.bbc.com/news/science-environment-29465446

The Hidden Earth: Undersea Mountains by the Thousands
http://www.slate.com/blogs/bad_astro...satellite.html


Makes perfect sense to me. Consider, the material of
the mount must be more dense than water. If its
mechanical strength evaporated it would droop down
to form a level plain. So there's more mass between
the peak and the center of the earth, and more
between mean sea level and the center also. More mass,
more gravity. It'll pull the sea surface towards
itself.

Clifford Heath.


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Default Heat sink grease

Once upon a time on usenet Mike S wrote:
On 4/21/2018 5:19 PM, wrote:
"Interesting. I remember reading that ocean water is higher near

underwater mountain tops due to increased gravitational attraction
and measurable from satellites,"

The would be one hell of a dense mountain to do that, I would think
it more likely to be because of a decreased gravitational pull being
forced away from the center of mass of the planet, due to its
inverse square relationship. But that is not my field of expertise.
(is anything ? the more I learn the less I know, if it weren't for
learning from mistakes I would be a babbling idiot - NO COMMENTS
FROM THE PEANUT GALLERY HERE !)
"I wonder if tanks could be designed with non-flat bottoms to
counteract what you mentioned"


Pretty sure that would not work because gravity is the leveling
force. As such the shape of the bottom should not matter. Perhaps at a
high altitude with a very large mass (dense, not
voluminous) placed under the center of the tank it could be
compensated. But then that makes splitting hairs look like hitting
the broad side of a barn with a planet.


I don't know the correct physics, just read a bit...

Satellite observations
The alternative is an indirect method that uses satellites fitted with
radar altimeters.
These spacecraft can infer the shape of the ocean bottom from the
shape of the water surface above.
Because water follows gravity, it is pulled into highs above the mass
of tall seamounts, and slumps into depressions over deep trenches.
http://www.bbc.com/news/science-environment-29465446

The Hidden Earth: Undersea Mountains by the Thousands
http://www.slate.com/blogs/bad_astro...satellite.html


Interesting, thanks.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)


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