| Topic: |
Science > Physics |
| User: |
"Jeffrey jhopkins4no" |
| Date: |
06 Feb 2005 01:37:33 AM |
| Object: |
Buoyancy on a submerged block on bottom of tank |
How is the Buoyancy on a block determined for the ideal case of a uniform
block submerged in a deep, flat bottom tank of water, where there's no water
below the block only around it and atop it - the block is placed flush with
the bottom of the tank?
--
Thanks,
Jeffrey
Beneath South Carolina skies and clouds
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| User: "Franz Heymann" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
06 Feb 2005 04:02:55 AM |
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"Jeffrey" <jhopkins4"no spam"@sc.rr.com> wrote in message
news:1PjNd.66535$fE4.11298072@twister.southeast.rr.com...
How is the Buoyancy on a block determined for the ideal case of a
uniform
block submerged in a deep, flat bottom tank of water, where there's
no water
below the block only around it and atop it - the block is placed
flush with
the bottom of the tank?
The weight lost by the block is always equal to the weight oif the
water it displaces, whether it is resting on the bottom or floating
freely or suspended by a piece of string.
Franz
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| User: "Gregory L. Hansen" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
06 Feb 2005 08:05:08 AM |
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In article <cu4q0e$ivf$1@sparta.btinternet.com>,
Franz Heymann <franz.heymann@btopenworld.com> wrote:
"Jeffrey" <jhopkins4"no spam"@sc.rr.com> wrote in message
news:1PjNd.66535$fE4.11298072@twister.southeast.rr.com...
How is the Buoyancy on a block determined for the ideal case of a
uniform
block submerged in a deep, flat bottom tank of water, where there's
no water
below the block only around it and atop it - the block is placed
flush with
the bottom of the tank?
The weight lost by the block is always equal to the weight oif the
water it displaces, whether it is resting on the bottom or floating
freely or suspended by a piece of string.
Franz
Hmm... weight lost? Depending on the definition of "flush with the bottom
of the tank" (e.g. is it a cork with the bottom exposed to atmosphere?)
there may be weight gained.
--
"Are those morons getting dumber or just louder?" -- Mayor Quimby
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| User: "Franz Heymann" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
06 Feb 2005 12:07:52 PM |
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"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
news:cu586k$ldr$3@rainier.uits.indiana.edu...
In article <cu4q0e$ivf$1@sparta.btinternet.com>,
Franz Heymann <franz.heymann@btopenworld.com> wrote:
"Jeffrey" <jhopkins4"no spam"@sc.rr.com> wrote in message
news:1PjNd.66535$fE4.11298072@twister.southeast.rr.com...
How is the Buoyancy on a block determined for the ideal case of a
uniform
block submerged in a deep, flat bottom tank of water, where
there's
no water
below the block only around it and atop it - the block is placed
flush with
the bottom of the tank?
The weight lost by the block is always equal to the weight oif the
water it displaces, whether it is resting on the bottom or floating
freely or suspended by a piece of string.
Franz
Hmm... weight lost? Depending on the definition of "flush with the
bottom
of the tank" (e.g. is it a cork with the bottom exposed to
atmosphere?)
there may be weight gained.
You've lost me.
Franz
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| User: "Gregory L. Hansen" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
06 Feb 2005 07:26:04 PM |
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In article <cu5mdn$655$2@sparta.btinternet.com>,
Franz Heymann <franz.heymann@btopenworld.com> wrote:
"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
news:cu586k$ldr$3@rainier.uits.indiana.edu...
In article <cu4q0e$ivf$1@sparta.btinternet.com>,
Franz Heymann <franz.heymann@btopenworld.com> wrote:
"Jeffrey" <jhopkins4"no spam"@sc.rr.com> wrote in message
news:1PjNd.66535$fE4.11298072@twister.southeast.rr.com...
How is the Buoyancy on a block determined for the ideal case of a
uniform
block submerged in a deep, flat bottom tank of water, where
there's
no water
below the block only around it and atop it - the block is placed
flush with
the bottom of the tank?
The weight lost by the block is always equal to the weight oif the
water it displaces, whether it is resting on the bottom or floating
freely or suspended by a piece of string.
Franz
Hmm... weight lost? Depending on the definition of "flush with the
bottom
of the tank" (e.g. is it a cork with the bottom exposed to
atmosphere?)
there may be weight gained.
You've lost me.
Franz
The bouyancy is the pressure dot normal integrated over the surface. If
there's no pressure on the bottom, it's not being pushed up.
Edward's flapper valve is a brilliant example. The valve floats, except
when it's closed and the tank is filled the weight of water keeps it down
and sealed. The flapper valve itself is a brilliant but seldom
appreciated peice of engineering-- so much functionality in a single
peice of rubber with a hinge. It's hard to make things look easy.
--
"Yes, I revere you much, honored ones, and wish to fart in response." --
Aristophanes, Clouds
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| User: "Edward Green" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
10 Feb 2005 06:10:06 PM |
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Gregory L. Hansen wrote:
Edward's flapper valve is a brilliant example.
Blush.
The valve floats, except
when it's closed and the tank is filled the weight of water keeps it
down
and sealed. The flapper valve itself is a brilliant but seldom
appreciated peice of engineering-- so much functionality in a single
peice of rubber with a hinge. It's hard to make things look easy.
Of course, I made it look a little two easy. If the valve were merely
at the bottom of the tank, the dynamic force of water rushing out of
the hole would presumably overwhelm the buoyancy and the valve would
reseat too soon. To prevent this seems to be the function of a barrier
surrounding the outlet, which meters the outflow and allows the valve
to float on the resulting free surface inside the barrier and near the
bottom of the tank.
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| User: "tj Frazir" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
10 Feb 2005 10:28:12 PM |
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shame on you all .
BOLT a scale to the bottom of the tank.
It will mesure a push up or down .
it has a flat plate and will b the tanks bottom.
IF its pulling the scle up ( and it is ) read the scale.
the amount of lift will not change if water gets under it or not.
no matter how you mount the scale as long as you wiegh the up or
down.
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| User: "Richard Herring" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
14 Feb 2005 04:21:21 AM |
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In message <1108080606.321078.114240@o13g2000cwo.googlegroups.com>,
Edward Green <spamspamspam3@netzero.com> writes
Gregory L. Hansen wrote:
Edward's flapper valve is a brilliant example.
Blush.
The valve floats, except
when it's closed and the tank is filled the weight of water keeps it
down
and sealed. The flapper valve itself is a brilliant but seldom
appreciated peice of engineering-- so much functionality in a single
peice of rubber with a hinge. It's hard to make things look easy.
Of course, I made it look a little two easy. If the valve were merely
at the bottom of the tank, the dynamic force of water rushing out of
the hole would presumably overwhelm the buoyancy and the valve would
reseat too soon. To prevent this seems to be the function of a barrier
surrounding the outlet, which meters the outflow and allows the valve
to float on the resulting free surface inside the barrier and near the
bottom of the tank.
Yet more complications ;-) And you haven't yet mentioned the main
drawback of the flap-valve. They leak, and make a variety of irritating
trickling noises.
Here in these islands we generally prefer the siphonic flush.
--
Richard Herring
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| User: "Edward Green" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
06 Feb 2005 12:11:41 PM |
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Gregory L. Hansen wrote:
In article <cu4q0e$ivf$1@sparta.btinternet.com>,
Franz Heymann <franz.heymann@btopenworld.com> wrote:
"Jeffrey" <jhopkins4"no spam"@sc.rr.com> wrote in message
news:1PjNd.66535$fE4.11298072@twister.southeast.rr.com...
How is the Buoyancy on a block determined for the ideal case of a
uniform
block submerged in a deep, flat bottom tank of water, where
there's
no water
below the block only around it and atop it - the block is placed
flush with
the bottom of the tank?
The weight lost by the block is always equal to the weight oif the
water it displaces, whether it is resting on the bottom or floating
freely or suspended by a piece of string.
Franz
Hmm... weight lost? Depending on the definition of "flush with the
bottom
of the tank" (e.g. is it a cork with the bottom exposed to
atmosphere?)
there may be weight gained.
Right. To spell it out in detail, resting on a normal sort of bottom,
with a bad seal, the pressure under the block is going to be the same
as if it were submerged to that depth regardless of the bottom. If
there is a seal, the pressure under the block may be any value, up to
one that would lift the block.
Along these lines, I was recently admiring the extreme cleverness of
the flapper/float valve found in many toilet tanks. The valve is
bouyant (contains an air pocket), and also seals an opening on the
bottom of the tank normally over air. When handle is activated a chain
pulls the valve off its seat, allowing water to rush down the hole. At
this point the valves natural buoyancy takes over, and it floats on the
surface of the water, so that it does not reseat immediately. When the
tank is sufficiently drained, the valve reseats, and the tank refills.
There are other features I have not described.
Although it seems like cheating, we could take this as an example of
reduced buoyancy for an object flush with the bottom of a tank.
.
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
06 Feb 2005 05:26:26 PM |
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Jeffrey Gravity is holding the block to the bottom of the tank of
water.Gravity is a down force. Buoyancy is an up force. Lets make the
block 14 cubic inches and made of gold. It weighs about a ton 14' cube
of water will say weighs 80 lb The force resting on the floor of the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic empty
container(just air in it) under water.(not easy) Gold is so very heavy
and that is why I used it to make my point. Bert Please don't flame me
on the size of gold to be a ton
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| User: "CWatters" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 02:40:49 AM |
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"G=EMC^2 Glazier" <herbertglazier@webtv.net> wrote in message
news:8578-4206A7A2-118@storefull-3177.bay.webtv.net...
Jeffrey Gravity is holding the block to the bottom of the tank of
water.Gravity is a down force. Buoyancy is an up force. Lets make the
block 14 cubic inches and made of gold. It weighs about a ton 14' cube
of water will say weighs 80 lb The force resting on the floor of the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic empty
container(just air in it) under water.(not easy) Gold is so very heavy
and that is why I used it to make my point. Bert Please don't flame me
on the size of gold to be a ton
The debate is about the effect (if any) of the floor....
What about something light? Your example suggests it's not possible to get a
block of wood (which normally floats) to remain "flush" on the bottom of a
tank of water.
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 07:37:06 AM |
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G=EMC^2 Glazier wrote:
Jeffrey Gravity is holding the block to the bottom of the tank of
water.Gravity is a down force. Buoyancy is an up force. Lets make the
block 14 cubic inches and made of gold. It weighs about a ton 14'
cube
of water will say weighs 80 lb The force resting on the floor of the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic empty
container(just air in it) under water.(not easy) Gold is so very
heavy
and that is why I used it to make my point. Bert Please don't flame
me
on the size of gold to be a ton
That's not right.
If what you were saying were right, then the most force a suction cup
on your desktop could exert would be its weight. Instead, it's the
weight of all the fluid (air, e.g.) on top of it.
PD
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| User: "CWatters" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 10:08:52 AM |
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"PD" <pdraper@yahoo.com> wrote in message
news:1107783426.908550.181430@g14g2000cwa.googlegroups.com...
G=EMC^2 Glazier wrote:
Jeffrey Gravity is holding the block to the bottom of the tank of
water.Gravity is a down force. Buoyancy is an up force. Lets make the
block 14 cubic inches and made of gold. It weighs about a ton 14'
cube
of water will say weighs 80 lb The force resting on the floor of the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic empty
container(just air in it) under water.(not easy) Gold is so very
heavy
and that is why I used it to make my point. Bert Please don't flame
me
on the size of gold to be a ton
That's not right.
If what you were saying were right, then the most force a suction cup
on your desktop could exert would be its weight. Instead, it's the
weight of all the fluid (air, e.g.) on top of it.
Good example.
.
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| User: "CWatters" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 10:17:07 AM |
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"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:ooMNd.5673$RM2.455809@phobos.telenet-ops.be...
"PD" <pdraper@yahoo.com> wrote in message
news:1107783426.908550.181430@g14g2000cwa.googlegroups.com...
G=EMC^2 Glazier wrote:
Jeffrey Gravity is holding the block to the bottom of the tank of
water.Gravity is a down force. Buoyancy is an up force. Lets make the
block 14 cubic inches and made of gold. It weighs about a ton 14'
cube
of water will say weighs 80 lb The force resting on the floor of the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic empty
container(just air in it) under water.(not easy) Gold is so very
heavy
and that is why I used it to make my point. Bert Please don't flame
me
on the size of gold to be a ton
That's not right.
If what you were saying were right, then the most force a suction cup
on your desktop could exert would be its weight. Instead, it's the
weight of all the fluid (air, e.g.) on top of it.
Good example.
...except I think he's right. The suction cup _does_ only exert it's weight
on the desk, but that's not the same thing as the dorce needed to remove it
which can be a lot larger.
A block of wood would remain on the bottom of the tank if the boyancy (as
calculated by PD's method) divided by the area was greater than the water
pressure. It wouldn't take much depth of water for the wood to stay on the
bottom.
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 06:34:35 PM |
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CWaters A suction cup works because energy removed the air inside the
cup. A hard hat diver only 32 feet under water can have his whole body
squeezed into the helmet(hat) because air pressure in his helmet became
less than the water pressure against his rubber suit. This is the same
physics of a suction cup. Bert PS Hard hat divers call that the
"big squeeze"
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| User: "Dave Baker" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 11:52:34 AM |
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CWatters <colin.watters@pandoraBOX.be> wrote in message
news:7wMNd.5676$vU1.362622@phobos.telenet-ops.be...
"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:ooMNd.5673$RM2.455809@phobos.telenet-ops.be...
"PD" <pdraper@yahoo.com> wrote in message
news:1107783426.908550.181430@g14g2000cwa.googlegroups.com...
G=EMC^2 Glazier wrote:
Jeffrey Gravity is holding the block to the bottom of the tank of
water.Gravity is a down force. Buoyancy is an up force. Lets make
the
block 14 cubic inches and made of gold. It weighs about a ton 14'
cube
of water will say weighs 80 lb The force resting on the floor of
the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic
empty
container(just air in it) under water.(not easy) Gold is so very
heavy
and that is why I used it to make my point. Bert Please don't flame
me
on the size of gold to be a ton
That's not right.
If what you were saying were right, then the most force a suction cup
on your desktop could exert would be its weight. Instead, it's the
weight of all the fluid (air, e.g.) on top of it.
Good example.
..except I think he's right. The suction cup _does_ only exert it's weight
on the desk, but that's not the same thing as the dorce needed to remove
it
which can be a lot larger.
A block of wood would remain on the bottom of the tank if the boyancy (as
calculated by PD's method) divided by the area was greater than the water
pressure. It wouldn't take much depth of water for the wood to stay on the
bottom.
It doesn't matter what the depth of water is. If there is no pressure acting
on the bottom of the block there is no boyancy. This is just another example
of the engineer's trick of 'wringing' two perfectly flat gauge blocks
together and showing that they then stick. In this case air has been totally
excluded from the interface so they are held together by atmospheric
pressure on the opposing surfaces.
In the case of a block at the bottom of a tank of water, if the block can be
'wrung' against the bottom of the tank so perfectly that it excludes water,
or alternatively if the joint is sealed with silicone or mastic then the
force holding it down becomes its own weight plus the pressure x area on the
top of the block. Even if the depth of water is negligible, or indeed not
even as high as the top of the block, its own weight remains as a downforce
plus atmospheric pressure x upper surface area of the block.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
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| User: "tj Frazir" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 06:33:15 PM |
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Gong even farther ,,the blck is now 20 feet tall and a bouyant force of
20 cubic feet.
Now the vaccume wount hold it.
is the downforce more or less than the buoyant force ?
Deep 2 has a cam off the shelf HD and put in corn oil and put a
busted light buld in a jar of gassoline and tured it on and looked at
the deepest point on earth with it.
I tested a cell phone in corn oil jar dropped i down 2 miles and back
and it works.
Stangest thing ,,the 5 foot wide crab we saw on a solonon island with a
25 inch shell ..
I ask around and n old dude says the japs liked the giant crabs for the
admerals table and it sank on a jap ship because they only cook them
alive and it was for the admeral .
That crab came from japan and sank on a ship and walked the bottom to
the island .
and learned to hunt birds.
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| User: "tj Frazir" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank idiots |
08 Feb 2005 10:36:26 AM |
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My BLOCK is 20 feet tall with a lift more thann a vaccume will hold back
..
THE BLOCK has lift if its moving or not.
I got rid of the bottom and the 20 foot tall square foot block still
floats up.
IDIOTS
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank idiots |
08 Feb 2005 11:22:40 AM |
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tj Frazir wrote:
My BLOCK is 20 feet tall with a lift more thann a vaccume will hold
back
.
THE BLOCK has lift if its moving or not.
I got rid of the bottom and the 20 foot tall square foot block still
floats up.
IDIOTS
Not a matter if it's moving.
If there is water under it, and the difference between the force
exerted by water pressure on the top and bottom of the blocks is
greater than the weight of the block, then it will float upward.
If there is no water under it -- none -- then there is no force upward
due to water acting on the bottom surface of the block. In this case,
there are three forces in the vertical direction:
1. The force of gravity acting on the block -- down.
2. The weight of all the fluid (water and air) sitting on top of the
block -- down.
3. The contact force of the aquarium pushing up exactly what it needs
to keep the block from penetrating the floor -- up.
That's it. There are no more.
It's wonderful how a simple example like this can uncover so many
misconceptions and half-understood principles.
PD
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| User: "tj Frazir" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank idiots |
08 Feb 2005 12:36:13 PM |
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Snip you off ..
NO water don't nead to be under it IDIOT.
A closed off tube is threw the bottom and nothing is pushing it up.
It may hold it down but wount PUSH it up.
The 4 inch tube of air sticks up in the tank 5 feet and has 40 pounds
of lift.
Nothing is pushing its bottom .
The end of the tube is not inthe water.
Its too stupid to coment on anyway ,,
but you morons are not getting it and its mormid as *****
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank idiots |
08 Feb 2005 01:21:01 PM |
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tj Frazir wrote:
Snip you off ..
NO water don't nead to be under it IDIOT.
A closed off tube is threw the bottom and nothing is pushing it up.
It may hold it down but wount PUSH it up.
The 4 inch tube of air sticks up in the tank 5 feet and has 40
pounds
of lift.
Nothing is pushing its bottom .
The end of the tube is not inthe water.
Its too stupid to coment on anyway ,,
but you morons are not getting it and its mormid as *****
A closed-off tube through the bottom of an aquarium, with its bottom
end below the bottom of the tank, and its top end submerged under the
water, will get pushed DOWN, not UP.
Idiot.
PD
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| User: "tj Frazir" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 06:17:00 PM |
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Some for some against .
The block is boyant and its lift is its displacement..
BUT ,,if it cant get water under it it wount mover BUT there is still
buoyant force.
If the capped tube passes thew and can slide threw the bottom without
water getting out.
near the bottom with only 1 foot up in the tank,,the water pushes it
down out of the tank .
But If I put 5 feet up in the tank the lift overcomed the push down
andthe tube floats its self up with nothing pushing at the bottom.
with it floating UP and nothing pushing up from under because it
passes threw the tanks bottom here no water can push it.
A vaccume from sitting th block down and preventing water from
getting under it works
better under water ,,sucksion cups work best underwater. But held down
by the water due to a vaccume dont mean theres no bouyancy.
Lack of changing methods is a lack of sci
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 10:46:37 AM |
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CWatters wrote:
"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:ooMNd.5673$RM2.455809@phobos.telenet-ops.be...
"PD" <pdraper@yahoo.com> wrote in message
news:1107783426.908550.181430@g14g2000cwa.googlegroups.com...
G=EMC^2 Glazier wrote:
Jeffrey Gravity is holding the block to the bottom of the tank
of
water.Gravity is a down force. Buoyancy is an up force. Lets
make the
block 14 cubic inches and made of gold. It weighs about a ton
14'
cube
of water will say weighs 80 lb The force resting on the floor
of the
tank. 2,000 lb less 80 lb. Jeffrey don't be fooled into
thinking
buoyancy is a weak up force,just try pushing a 14 cubic plastic
empty
container(just air in it) under water.(not easy) Gold is so
very
heavy
and that is why I used it to make my point. Bert Please don't
flame
me
on the size of gold to be a ton
That's not right.
If what you were saying were right, then the most force a suction
cup
on your desktop could exert would be its weight. Instead, it's
the
weight of all the fluid (air, e.g.) on top of it.
Good example.
..except I think he's right. The suction cup _does_ only exert it's
weight
on the desk, but that's not the same thing as the dorce needed to
remove it
which can be a lot larger.
A block of wood would remain on the bottom of the tank if the boyancy
(as
calculated by PD's method) divided by the area was greater than the
water
pressure. It wouldn't take much depth of water for the wood to stay
on the
bottom.
The critical point is that the buoyancy force calculation PRESUMES that
the fluid is in contact with all surface of the object. For a cube, for
example, the buoyancy force stems *directly* from the difference
between the pressure exerted by the fluid on the top and bottom
surfaces of the cube. There is no "magic" buoyancy force caused by
displacement of fluid -- it just happens to equal the weight of the
displaced fluid and therefore serves as a handy mnemonic.
If there IS NO fluid in contact with the bottom of the cube, then there
IS NO buoyancy force, and including one in a free body diagram of the
cube would lead to an error.
PD
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
07 Feb 2005 06:52:31 PM |
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RD If the cube can be compressed as it goes deeper(less volume) its up
force of bouyantcy would be less. Deep enough and an air bubble can be
squeezed to a point where they will not rise. In scuba diving your
air bubbles get smaller and smaller the deeper down you go,and also rise
much slower. Best to make a diving bell round because water pressure is
equal top bottom and sides. An interesting question would be. Water is
basically non compressible,but could water molecules move closer
together say 35,000 feet down??? Bert
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 07:59:07 AM |
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Well gentleman my pet white octopus "Moby" tells me a flat block lying
on the very flat bottom does not create any suction. He also knows that
even as you think there is no water pressure pushing this object up from
its bottom the water pressure is just as equal at the bottom as any
where else. Think only how bouyantcy works. Moby can use some of his
body energy to create suction in his cups. Can climb up the glass sides
of his tank. Can create friction with these suction cups to walk across
6 feet to my wifes exotic fish tank,and get into the tank eat her most
expensive fish and be back in his tank before sun rise. Well Moby
should know since he is the smartest,and most popular octupus in the
world.Last week he was in Time mag science section Those that would
like a picture of my Moby let me know by email Bert
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 08:51:00 AM |
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G=EMC^2 Glazier wrote:
Well gentleman my pet white octopus "Moby" tells me a flat block
lying
on the very flat bottom does not create any suction.
Depends on whether any water seeps under the block. If you have smooth
glass and a smooth metal block and you press the block to the glass,
you'll be suprised to find that it's held there as firmly as a suction
cup would be, and for exactly the same reason.
He also knows that
even as you think there is no water pressure pushing this object up
from
its bottom the water pressure is just as equal at the bottom as any
where else. Think only how bouyantcy works. Moby can use some of his
body energy to create suction in his cups. Can climb up the glass
sides
of his tank. Can create friction with these suction cups to walk
across
6 feet to my wifes exotic fish tank,and get into the tank eat her
most
You're right about the friction, but you also have to consider this
chain of thinking.
Friction is not caused by suction directly.
Friction is a coefficient (determined by the two surfaces in contact)
times the contact force one surface exerts on the other.
Suction is not a force.
What is pushing the suction cup onto the glass is the water pressure
(or air pressure, outside the tank) pushing on the TOP of the suction
cup. The glass has to push back, and this is what determines the
contact force between the glass and the BOTTOM of the suction cup.
PD
expensive fish and be back in his tank before sun rise. Well Moby
should know since he is the smartest,and most popular octupus in the
world.Last week he was in Time mag science section Those that
would
like a picture of my Moby let me know by email Bert
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| User: "CWatters" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 08:59:43 AM |
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"PD" <pdraper@yahoo.com> wrote in message
news:1107874260.519333.89040@z14g2000cwz.googlegroups.com...
G=EMC^2 Glazier wrote:
Well gentleman my pet white octopus "Moby" tells me a flat block
lying
on the very flat bottom does not create any suction.
Depends on whether any water seeps under the block.
Does the viscosity of the water matter?
How about a bit of oil under the block?
How about a bit of glass (a rather viscous liquid)?
How about the bottom of the tank itself?
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 09:06:36 AM |
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CWatters wrote:
"PD" <pdraper@yahoo.com> wrote in message
news:1107874260.519333.89040@z14g2000cwz.googlegroups.com...
G=EMC^2 Glazier wrote:
Well gentleman my pet white octopus "Moby" tells me a flat block
lying
on the very flat bottom does not create any suction.
Depends on whether any water seeps under the block.
Does the viscosity of the water matter?
Not as much as the surface tension.
How about a bit of oil under the block?
No.
How about a bit of glass (a rather viscous liquid)?
Not sure what you mean.
How about the bottom of the tank itself?
Not sure what you mean.
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| User: "CWatters" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 11:23:23 AM |
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"PD" <pdraper@yahoo.com> wrote in message
news:1107875196.917252.100640@f14g2000cwb.googlegroups.com...
How about the bottom of the tank itself?
Not sure what you mean.
I was trying to make the point that the material under the block (water,
oil, glass or metal tank) shouldn't make any difference... or does it?
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| User: "PD" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 11:48:24 AM |
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CWatters wrote:
"PD" <pdraper@yahoo.com> wrote in message
news:1107875196.917252.100640@f14g2000cwb.googlegroups.com...
How about the bottom of the tank itself?
Not sure what you mean.
I was trying to make the point that the material under the block
(water,
oil, glass or metal tank) shouldn't make any difference... or does
it?
Sure it does. If it's a fluid, then it can transmit fluid pressure. If
it's a solid, then no. Glass can't be considered a fluid in this
context.
The definition of a fluid, for this purpose, is that an infinitesimal
(or, if you don't like that word, use "small enough") chunk of fluid
exerts pressure equally over the surface of the chunk.
Sorry, I didn't get your drift initially.
PD
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Buoyancy on a submerged block on bottom of tank |
08 Feb 2005 02:47:59 PM |
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PD Right you are suction is a push force. Take the air out of a can and
the 14.7 lb psi pressure will push its sides in. Take a flat piece of
glass wet it place another flat glass on top of it,and the only way you
can separate them is sliding them apart. That begs these questions "Did
the water molecules act like suction cups?" Are we seeing the cohesion
force created by molecules interacting with each other(close contact)
because of the flatness of these two surfaces?. Does this bonding help
if both surfaces touching are made of the same molecules? How does
gravity fit in? How does magnetisum fit in? Could there be an
electro-magnetic attraction?(static electricity) Could all of
the above be different parts to the answer PD wants? Could Moby be
wrong even when his species has lived on the oceans floors millions of
years longer than humankind been on Earths surface. Always best to think
in every direction. This would be a very easy experiment. I think
Feynman would like to do it. If the box got positive bouyantcy will
it rise off the tank floor? Or would it not? Moby and I want to know
Bert
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