| Topic: |
Science > Physics |
| User: |
"Cliff" |
| Date: |
21 Aug 2006 10:16:58 PM |
| Object: |
Physics of Settling? |
I observed a phenomenon today I'd like to know more about.
Unfortunately, I don't even know the search terms to use, so any
pointers about where I should start reading would be very appreciated!
One can buy 6mm plastic spheres for use as ammunition in an air pistol.
There are at least two densities of plastic used: one yields a 0.12g
sphere, and another yields a 0.20g sphere. While trying to make a
demonstration for a 9th grade science class, I mixed some 0.20g spheres
with some 0.12g spheres in roughly equal proportion. I had hoped that
the density difference was great enough that with gentle agitation the
spheres would separate into two well-defined layers, but the degree of
separation was disappointing.
I then placed the mixture of spheres into water and discovered that the
0.12g spheres were only slightly more dense than water. (In fact, the
low-density plastic was sufficiently hydrophobic that the spheres
tended to clump together, cling to air bubbles, and "float" by surface
tension. It took a drop or two of soap to actually make them behave.)
Under these conditions, it's actually hard to achieve a relatively
homogeneous mixture of the spheres to start my demo because the
high-density spheres move so quickly to the bottom of the container.
The few low-density spheres that get trapped among the high-density
ones do separate out a little more easily, but given the relative net
downward force on each sphere under water, I had expected a big
difference.
Clearly I don't really understand what's going on with settling. I'd
like to learn a little about how to quantify "ease of separating" the
spheres through settling and what factors influence the phenomenon.
Thanks!
Cliff
.
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|
| User: "Sorcerer" |
|
| Title: Re: Physics of Settling? |
21 Aug 2006 11:43:34 PM |
|
|
"Cliff" <hcbowman@gmail.com> wrote in message
news:1156216618.818492.150880@h48g2000cwc.googlegroups.com...
|I observed a phenomenon today I'd like to know more about.
| Unfortunately, I don't even know the search terms to use, so any
| pointers about where I should start reading would be very appreciated!
|
| One can buy 6mm plastic spheres for use as ammunition in an air pistol.
| There are at least two densities of plastic used: one yields a 0.12g
| sphere, and another yields a 0.20g sphere. While trying to make a
| demonstration for a 9th grade science class, I mixed some 0.20g spheres
| with some 0.12g spheres in roughly equal proportion. I had hoped that
| the density difference was great enough that with gentle agitation the
| spheres would separate into two well-defined layers, but the degree of
| separation was disappointing.
|
| I then placed the mixture of spheres into water and discovered that the
| 0.12g spheres were only slightly more dense than water. (In fact, the
| low-density plastic was sufficiently hydrophobic that the spheres
| tended to clump together, cling to air bubbles, and "float" by surface
| tension. It took a drop or two of soap to actually make them behave.)
| Under these conditions, it's actually hard to achieve a relatively
| homogeneous mixture of the spheres to start my demo because the
| high-density spheres move so quickly to the bottom of the container.
| The few low-density spheres that get trapped among the high-density
| ones do separate out a little more easily, but given the relative net
| downward force on each sphere under water, I had expected a big
| difference.
|
| Clearly I don't really understand what's going on with settling. I'd
| like to learn a little about how to quantify "ease of separating" the
| spheres through settling and what factors influence the phenomenon.
|
| Thanks!
|
| Cliff
I'm not sure what you are trying to achieve.
Are you attempting a simulation of some existing industrial process
such as separation of different hydrocarbons? Write a theory?
Do you want separation or no separation?
Have you tried boiling the water to retard separation?
You say this is for a 9th grade science class, but what
are you expecting them to learn? How to experiment?
If so, then the problem as you have it is fine. What is your objective?
You've obviously discovered some of the factors involved,
such as clumping, air bubbles and relative density with respect
to the medium, soapy water. Other considerations might be a
centrifuge, salt water, crude oil, washing up liquid, gasoline... the list
is huge.
Try diced carrot and potato in water, that separates, but I don't
know if you have to take hygiene into consideration.
Androcles
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|
| User: "Dirk Van de moortel" |
|
| Title: Re: Physics of Settling? |
22 Aug 2006 11:32:23 AM |
|
|
"Cliff" <hcbowman@gmail.com> wrote in message news:1156216618.818492.150880@h48g2000cwc.googlegroups.com...
I observed a phenomenon today I'd like to know more about.
Unfortunately, I don't even know the search terms to use, so any
pointers about where I should start reading would be very appreciated!
One can buy 6mm plastic spheres for use as ammunition in an air pistol.
There are at least two densities of plastic used: one yields a 0.12g
sphere, and another yields a 0.20g sphere. While trying to make a
demonstration for a 9th grade science class, I mixed some 0.20g spheres
with some 0.12g spheres in roughly equal proportion. I had hoped that
the density difference was great enough that with gentle agitation the
spheres would separate into two well-defined layers, but the degree of
separation was disappointing.
I then placed the mixture of spheres into water and discovered that the
0.12g spheres were only slightly more dense than water. (In fact, the
low-density plastic was sufficiently hydrophobic that the spheres
tended to clump together, cling to air bubbles, and "float" by surface
tension. It took a drop or two of soap to actually make them behave.)
Under these conditions, it's actually hard to achieve a relatively
homogeneous mixture of the spheres to start my demo because the
high-density spheres move so quickly to the bottom of the container.
The few low-density spheres that get trapped among the high-density
ones do separate out a little more easily, but given the relative net
downward force on each sphere under water, I had expected a big
difference.
Clearly I don't really understand what's going on with settling. I'd
like to learn a little about how to quantify "ease of separating" the
spheres through settling and what factors influence the phenomenon.
Thanks!
I think the size of the spheres is *much* more important than the weight.
Try to mix small and big marbles in a bucket:
http://groups.google.com/group/sci.physics/msg/f751afc0c1f45142
http://groups.google.com/group/sci.physics/msg/cdd286ab2472f818
Make sure you don't wake the neighbours ;-)
Dirk Vdm
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|
| User: "Weatherlawyer" |
|
| Title: Re: Physics of Settling? |
28 Aug 2006 02:47:16 AM |
|
|
Cliff wrote:
I observed a phenomenon today I'd like to know more about.
Unfortunately, I don't even know the search terms to use, so any
pointers about where I should start reading would be very appreciated!
One can buy 6mm plastic spheres for use as ammunition in an air pistol.
There are at least two densities of plastic used: one yields a 0.12g
sphere, and another yields a 0.20g sphere. While trying to make a
demonstration for a 9th grade science class, I mixed some 0.20g spheres
with some 0.12g spheres in roughly equal proportion. I had hoped that
the density difference was great enough that with gentle agitation the
spheres would separate into two well-defined layers, but the degree of
separation was disappointing.
I then placed the mixture of spheres into water and discovered that the
0.12g spheres were only slightly more dense than water. (In fact, the
low-density plastic was sufficiently hydrophobic that the spheres
tended to clump together, cling to air bubbles, and "float" by surface
tension. It took a drop or two of soap to actually make them behave.)
Under these conditions, it's actually hard to achieve a relatively
homogeneous mixture of the spheres to start my demo because the
high-density spheres move so quickly to the bottom of the container.
The few low-density spheres that get trapped among the high-density
ones do separate out a little more easily, but given the relative net
downward force on each sphere under water, I had expected a big
difference.
Clearly I don't really understand what's going on with settling. I'd
like to learn a little about how to quantify "ease of separating" the
spheres through settling and what factors influence the phenomenon.
Then there is the mixtures of mixings such as rattling quicksand. Make
a set of quick sand apparatus out of pop bottles and hose pipes. And
using a drill with an allen key or somesuch variable speed whacker, see
what unsettles.
.
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|
| User: "Bruce Scott TOK" |
|
| Title: Re: Physics of Settling? |
22 Aug 2006 06:38:42 AM |
|
|
Cliff wrote:
I observed a phenomenon today I'd like to know more about.
Unfortunately, I don't even know the search terms to use, so any
pointers about where I should start reading would be very appreciated!
One can buy 6mm plastic spheres for use as ammunition in an air pistol.
There are at least two densities of plastic used: one yields a 0.12g
sphere, and another yields a 0.20g sphere. While trying to make a
demonstration for a 9th grade science class, I mixed some 0.20g spheres
with some 0.12g spheres in roughly equal proportion. I had hoped that
the density difference was great enough that with gentle agitation the
spheres would separate into two well-defined layers, but the degree of
separation was disappointing.
[...]
Were the spheres the same size?
A phenomenon in this case at least as strong as the density effects is
the size sorting that comes from the details of packing. Google for
``why the brazil nuts rise to the top'' to find all you need.
Recently there is some interesting investigation into the competition
between percolation and condensation, according to which this ``Brazil
Nut Effect'' can be reversed. A more technical buzzword in use is
``particle size segregation.''
The first paper on this I noticed was
Rosato, A., Strandburg, K. J., Prinz, F. & Swendsen, R. H.
``Why the Brazil Nuts are On Top: Size Segregation of Particulate
Matter by Shaking.''
Physical Review Letters 58, 1038-1040 (1987).
but there are reviews in the 1970s, including
Williams, J. C.
``The Segregation of Particulate Materials. A Review.''
Powder Technology 15, 245-251 (1976).
--
ciao,
Bruce
drift wave turbulence: http://www.rzg.mpg.de/~bds/
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|
|
| User: "Cliff" |
|
| Title: Re: Physics of Settling? |
22 Aug 2006 02:30:19 PM |
|
|
Bruce Scott TOK wrote:
Were the spheres the same size?
A phenomenon in this case at least as strong as the density effects is
the size sorting that comes from the details of packing. Google for
``why the brazil nuts rise to the top'' to find all you need.
[...]
ciao,
Bruce
Thanks to both Bruce and John for pointing me to "Brazil Nuts." Not
the first search term I would have guessed...
Actually, the spheres are all 6mm in diameter (nominal -- I don't know
the variance), so size shouldn't be the predominating factor. The
particle-size sorting is pretty cool, though.
--Cliff
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|
| User: "Andy Resnick" |
|
| Title: Re: Physics of Settling? |
22 Aug 2006 08:05:28 AM |
|
|
Cliff wrote:
I observed a phenomenon today I'd like to know more about.
Unfortunately, I don't even know the search terms to use, so any
pointers about where I should start reading would be very appreciated!
<snip>
Clearly I don't really understand what's going on with settling. I'd
like to learn a little about how to quantify "ease of separating" the
spheres through settling and what factors influence the phenomenon.
You have stumbled into an extremely active area of current research-
granular media, colloids, condensed matter, all kinds of things. It's
all really exciting, and covers topics like photonic bandgap materials,
phase transitions and critical points, glass dynamics, and foundations
of hydrodynamics.
Basically, what you have is a model system- an experimental system that
can be used to model other systems in a very generic way. I can't be
more specific than that unless I know more about your comfort level.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.
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|
|
| User: "Cliff" |
|
| Title: Re: Physics of Settling? |
22 Aug 2006 02:43:34 PM |
|
|
Andy Resnick wrote:
You have stumbled into an extremely active area of current research-
granular media, colloids, condensed matter, all kinds of things. It's
all really exciting, and covers topics like photonic bandgap materials,
phase transitions and critical points, glass dynamics, and foundations
of hydrodynamics.
Basically, what you have is a model system- an experimental system that
can be used to model other systems in a very generic way. I can't be
more specific than that unless I know more about your comfort level.
Thanks, Andrew. I'd like to know a little more.
The immediate goal is to make plausible the "heterogeneous accretion"
theory of the formation of the Earth. If the post big bang dust cloud
was reasonably well-mixed, why does the Earth have a well-defined iron
core and a silicate crust? But that's my 9th grade science class, and
I'll figure out a demo eventually.
I'm really interested in the behavior of these silly plastic spheres in
my failed demo, and reading about some less-silly examples is exactly
where I'd like to go. Most applied math is pretty familiar, but I'd
need primer materials on the three specific areas you mention in order
to get a handle on the terminology and principles.
Thanks for your time!
--Cliff
.
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|
|
| User: "Llanzlan Klazmon" |
|
| Title: Re: Physics of Settling? |
22 Aug 2006 07:04:56 PM |
|
|
"Cliff" <hcbowman@gmail.com> wrote in news:1156275814.758356.141060@
75g2000cwc.googlegroups.com:
Andy Resnick wrote:
You have stumbled into an extremely active area of current research-
granular media, colloids, condensed matter, all kinds of things. It's
all really exciting, and covers topics like photonic bandgap materials,
phase transitions and critical points, glass dynamics, and foundations
of hydrodynamics.
Basically, what you have is a model system- an experimental system that
can be used to model other systems in a very generic way. I can't be
more specific than that unless I know more about your comfort level.
Thanks, Andrew. I'd like to know a little more.
The immediate goal is to make plausible the "heterogeneous accretion"
theory of the formation of the Earth. If the post big bang dust cloud
was reasonably well-mixed, why does the Earth have a well-defined iron
core and a silicate crust? But that's my 9th grade science class, and
I'll figure out a demo eventually.
I suspect the separation occurs when the protoplanet gets large enough to
melt, either through the heat of formation, or radioactive decay or both.
Apparently, this is because molten iron/nickle and molten silicates are
immiscible. cf iron smelting - the slag floats to the surface. I'm sure
it's a bit more complicated than that though. BTW the Earth did not form
from primordial material produced by the big bang. In fact no dust of any
significance was produced by the big bang. Primordial material is believed
to be almost exclusively hydrogen and helium (a trace of Lithium) and the
unknown "dark matter". The bulk of the Earth's material was produced by
nuclear reactions in stars. The iron, probably sourced from supernova
detonations, as iron is produced only by high mass stars (which requires a
supernova to eject the iron from the stars core, or else a type 1a
supernova in which the bulk of a white dwarf star's mass is converted into
iron as the star itself is destroyed).
I'm really interested in the behavior of these silly plastic spheres in
my failed demo, and reading about some less-silly examples is exactly
where I'd like to go. Most applied math is pretty familiar, but I'd
need primer materials on the three specific areas you mention in order
to get a handle on the terminology and principles.
It's obviously far from a trivial question. Good luck with your research.
Klazmon.
Thanks for your time!
--Cliff
.
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|
| User: "Andy Resnick" |
|
| Title: Re: Physics of Settling? |
23 Aug 2006 08:11:12 AM |
|
|
Cliff wrote:
<snip>
I'm really interested in the behavior of these silly plastic spheres in
my failed demo, and reading about some less-silly examples is exactly
where I'd like to go. Most applied math is pretty familiar, but I'd
need primer materials on the three specific areas you mention in order
to get a handle on the terminology and principles.
Thanks for your time!
Check out the following homepages, they would be a good place to start:
http://www.deas.harvard.edu/projects/weitzlab/
http://physics.uchicago.edu/x_cond.html#Nagel
http://www.physics.upenn.edu/duriangroup/index.htm
http://chaos.utexas.edu/swinney.html
Most of these people have links to their papers where you can get
additional information. Swinney, for example, has a paper on size
segregation:
http://arxiv.org/abs/cond-mat/0601179
For the specific issue of planetary accretion, that's outside my field,
so I don't know a good place to start (other than browing say,
Astrophysical Journal).
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.
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|
| User: "Greg Hansen" |
|
| Title: Re: Physics of Settling? |
23 Aug 2006 11:08:56 AM |
|
|
Cliff wrote:
Andy Resnick wrote:
You have stumbled into an extremely active area of current research-
granular media, colloids, condensed matter, all kinds of things. It's
all really exciting, and covers topics like photonic bandgap materials,
phase transitions and critical points, glass dynamics, and foundations
of hydrodynamics.
Basically, what you have is a model system- an experimental system that
can be used to model other systems in a very generic way. I can't be
more specific than that unless I know more about your comfort level.
Thanks, Andrew. I'd like to know a little more.
The immediate goal is to make plausible the "heterogeneous accretion"
theory of the formation of the Earth. If the post big bang dust cloud
was reasonably well-mixed, why does the Earth have a well-defined iron
core and a silicate crust? But that's my 9th grade science class, and
I'll figure out a demo eventually.
I'm really interested in the behavior of these silly plastic spheres in
my failed demo, and reading about some less-silly examples is exactly
where I'd like to go. Most applied math is pretty familiar, but I'd
need primer materials on the three specific areas you mention in order
to get a handle on the terminology and principles.
Thanks for your time!
--Cliff
It occurs to me that if you have mild shaking, that could give them
enough mobility to sort. But violent shaking, like putting a can of
them on a paint shaker, would mix them pretty thoroughly.
If you can, you might play with frequency and amplitude of shaking, and
take samples from the top and bottom and count the number of each kind
to determine effectiveness of separation. And then, heck, if it's an
extremely active area of research, you might be able to get a published
article out of it.
.
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|
|
| User: "Andy Resnick" |
|
| Title: Re: Physics of Settling? |
24 Aug 2006 08:15:22 AM |
|
|
Greg Hansen wrote:
<snip>
It occurs to me that if you have mild shaking, that could give them
enough mobility to sort. But violent shaking, like putting a can of
them on a paint shaker, would mix them pretty thoroughly.
That's where it gets tricky- particles can only move if there is a
cavity for them to move *into*. So motion of particles is correlated,
and we can say there is a 'jamming' transition where particles can't
move at all because the other particles can't move out of the way, and
they can't move out of the way because those *other* particles are in
the way, etc. etc.
http://prola.aps.org/abstract/PRE/v48/i5/p3290_1
http://www.arxiv.org/abs/cond-mat/0412120
http://www.engin.umich.edu/dept/che/research/glotzer/
Here's a simple experiment: fill an open container with sand, or flour,
or pellets, whatever. Then, simply tap the container on the table over
and over while measuring the height of the media filling the container.
What you will find is that the level settles at a logarithmic rate.
And at some point, you are putting more energy into the system by
tapping that is given off by settling.
If you can, you might play with frequency and amplitude of shaking, and
take samples from the top and bottom and count the number of each kind
to determine effectiveness of separation. And then, heck, if it's an
extremely active area of research, you might be able to get a published
article out of it.
Just doing experiments with spheres gives all kinds of interesting
results. Now make them ellipsoids, or rods, given them size
distributions rather than discrete sizes, etc. etc.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.
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| User: "" |
|
| Title: Re: Physics of Settling? |
27 Aug 2006 04:31:02 AM |
|
|
In article <eck8lj$1d9$1@eeyore.INS.cwru.edu>,
Andy Resnick <andy.resnick@op.case.edu> wrote:
Greg Hansen wrote:
<snip>
It occurs to me that if you have mild shaking, that could give them
enough mobility to sort. But violent shaking, like putting a can of
them on a paint shaker, would mix them pretty thoroughly.
That's where it gets tricky- particles can only move if there is a
cavity for them to move *into*. So motion of particles is correlated,
and we can say there is a 'jamming' transition where particles can't
move at all because the other particles can't move out of the way, and
they can't move out of the way because those *other* particles are in
the way, etc. etc.
http://prola.aps.org/abstract/PRE/v48/i5/p3290_1
http://www.arxiv.org/abs/cond-mat/0412120
http://www.engin.umich.edu/dept/che/research/glotzer/
Here's a simple experiment: fill an open container with sand, or flour,
or pellets, whatever. Then, simply tap the container on the table over
and over while measuring the height of the media filling the container.
What you will find is that the level settles at a logarithmic rate.
Logarithmic? Next time I fill the flour canister I'll watch.
And at some point, you are putting more energy into the system by
tapping that is given off by settling.
Yes, that's true with flour.
If you can, you might play with frequency and amplitude of shaking, and
take samples from the top and bottom and count the number of each kind
to determine effectiveness of separation. And then, heck, if it's an
extremely active area of research, you might be able to get a published
article out of it.
Just doing experiments with spheres gives all kinds of interesting
results. Now make them ellipsoids, or rods, given them size
distributions rather than discrete sizes, etc. etc.
Another opportunity to play with food. A can of mixed nuts
should be ineresting.
/BAH
.
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| User: "" |
|
| Title: Re: Physics of Settling? |
24 Aug 2006 04:22:59 AM |
|
|
In article <44EC7D98.3000108@tcq.net>, Greg Hansen <glhansen@tcq.net> wrote:
Cliff wrote:
Andy Resnick wrote:
You have stumbled into an extremely active area of current research-
granular media, colloids, condensed matter, all kinds of things. It's
all really exciting, and covers topics like photonic bandgap materials,
phase transitions and critical points, glass dynamics, and foundations
of hydrodynamics.
Basically, what you have is a model system- an experimental system that
can be used to model other systems in a very generic way. I can't be
more specific than that unless I know more about your comfort level.
Thanks, Andrew. I'd like to know a little more.
The immediate goal is to make plausible the "heterogeneous accretion"
theory of the formation of the Earth. If the post big bang dust cloud
was reasonably well-mixed, why does the Earth have a well-defined iron
core and a silicate crust? But that's my 9th grade science class, and
I'll figure out a demo eventually.
I'm really interested in the behavior of these silly plastic spheres in
my failed demo, and reading about some less-silly examples is exactly
where I'd like to go. Most applied math is pretty familiar, but I'd
need primer materials on the three specific areas you mention in order
to get a handle on the terminology and principles.
Thanks for your time!
--Cliff
It occurs to me that if you have mild shaking, that could give them
enough mobility to sort. But violent shaking, like putting a can of
them on a paint shaker, would mix them pretty thoroughly.
If you can, you might play with frequency and amplitude of shaking, and
take samples from the top and bottom and count the number of each kind
to determine effectiveness of separation. And then, heck, if it's an
extremely active area of research, you might be able to get a published
article out of it.
Doing this with a paint can is fun. I've a color that seems to
separate easily. Instead of using a stick, I've been playing
at jostling the can in various ways. YOu can see the pattern of
mixing on the top. One of the coolest ways was rotating the
can back and forth 90-180 degrees. The drift of the color
that won't mix to the most staid part of the surface is
really intersting. It was not what I expected but could
be due to the fact that I was jostling the can with my
hand.
/BAH
.
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|
|
| User: "Andy Resnick" |
|
| Title: Re: Physics of Settling? |
24 Aug 2006 08:17:58 AM |
|
|
wrote:
<snip>
Doing this with a paint can is fun. I've a color that seems to
separate easily. Instead of using a stick, I've been playing
at jostling the can in various ways. YOu can see the pattern of
mixing on the top. One of the coolest ways was rotating the
can back and forth 90-180 degrees. The drift of the color
that won't mix to the most staid part of the surface is
really intersting. It was not what I expected but could
be due to the fact that I was jostling the can with my
hand.
You are right, it's totally non-intuitive. I had to do a quick
experiment recently, showing that the flow induced by orbital shaking is
much smaller than is expected. Similarly, you are finding that the
velocity must diffuse into the bulk- what you did is Stokes' second problem.
Mixing is not so simple!
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.
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| User: "" |
|
| Title: Re: Physics of Settling? |
26 Aug 2006 04:56:17 AM |
|
|
In article <eck8q7$1d9$2@eeyore.INS.cwru.edu>,
Andy Resnick <andy.resnick@op.case.edu> wrote:
jmfbahciv@aol.com wrote:
<snip>
Doing this with a paint can is fun. I've a color that seems to
separate easily. Instead of using a stick, I've been playing
at jostling the can in various ways. YOu can see the pattern of
mixing on the top. One of the coolest ways was rotating the
can back and forth 90-180 degrees. The drift of the color
that won't mix to the most staid part of the surface is
really intersting. It was not what I expected but could
be due to the fact that I was jostling the can with my
hand.
You are right, it's totally non-intuitive. I had to do a quick
experiment recently, showing that the flow induced by orbital shaking is
much smaller than is expected. Similarly, you are finding that the
velocity must diffuse into the bulk- what you did is Stokes' second problem.
Kewl! It even has a name.
Mixing is not so simple!
Especially reproducing it.
I thought about the paint mixing yesterday. Another thing to try,
but I can't figure out how, is to "see" if the different colors
mix differently (I'm not writing this well). I noticed that
coffee can covers that were dyed were much more difficult for
my hands to pry off than the white lids. My hypothese was that
the color created more stiffness but had no way to verify.
Then I started wondering if colored balls (like some guy is talking
about here) that are the same size should act the same. I'm
not sure they would. Query: would color make the mass differ?
If light had mass then just the color would have an effect.
But it must be the solution of the dye that has a different mass.
/BAH
.
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|
|
| User: "Greg Hansen" |
|
| Title: Re: Physics of Settling? |
26 Aug 2006 09:32:17 AM |
|
|
wrote:
In article <eck8q7$1d9$2@eeyore.INS.cwru.edu>,
Andy Resnick <andy.resnick@op.case.edu> wrote:
I thought about the paint mixing yesterday. Another thing to try,
but I can't figure out how, is to "see" if the different colors
mix differently (I'm not writing this well). I noticed that
coffee can covers that were dyed were much more difficult for
my hands to pry off than the white lids. My hypothese was that
the color created more stiffness but had no way to verify.
The color doesn't determine the properties, although it reflects them.
The lid was colored by adding stuff to it. Possibly including titanium
dioxide powder for opacity. Plasticine clay loaded with BBs is stiffer
than plasticine clay without, and I'd expect plastic loaded with powder
is stiff than plastic without.
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| User: "" |
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| Title: Re: Physics of Settling? |
27 Aug 2006 04:28:09 AM |
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In article <44F05B71.1060102@tcq.net>, Greg Hansen <glhansen@tcq.net> wrote:
jmfbahciv@aol.com wrote:
In article <eck8q7$1d9$2@eeyore.INS.cwru.edu>,
Andy Resnick <andy.resnick@op.case.edu> wrote:
I thought about the paint mixing yesterday. Another thing to try,
but I can't figure out how, is to "see" if the different colors
mix differently (I'm not writing this well). I noticed that
coffee can covers that were dyed were much more difficult for
my hands to pry off than the white lids. My hypothese was that
the color created more stiffness but had no way to verify.
The color doesn't determine the properties, although it reflects them.
The lid was colored by adding stuff to it. Possibly including titanium
dioxide powder for opacity. Plasticine clay loaded with BBs is stiffer
than plasticine clay without, and I'd expect plastic loaded with powder
is stiff than plastic without.
Thank you :-). [emoticon checks off another mystery of life]
Stupid question: Would round balls, where stiffness isn't part
of the dynamic, behave differently if they were different colors?
Would stiffness not be part of the dynamic?
We used to figure all this out when we were kids. :-) We just
couldn't put the math to it.
/BAH
/BAH
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| User: "Andy Resnick" |
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| Title: Re: Physics of Settling? |
29 Aug 2006 01:38:38 PM |
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wrote:
<snip>
Thank you :-). [emoticon checks off another mystery of life]
Stupid question: Would round balls, where stiffness isn't part
of the dynamic, behave differently if they were different colors?
Would stiffness not be part of the dynamic?
Sort of, but only when the particles approach the wavelength of light, a
micron or so. That's the basis for 'photonic bandgap materials' in that
there are certain directions that light can no longer propagate, in
analogy to electronic bandgaps.
If you then dope the material with fluorescent particles, you can affect
the excitation lifetime. If the material is made from for example, a
liquid crystal emulsion with the liquid crystal drops in a nematic,
smectic, or cholesteric phase, then other things can happen. It's
easier to think of materials to make than to predict what the
macroscopic properties will be. Ellipsoidal particles, binary alloys,
rods, discs, dielectric particles, conducting particles, etc. etc. Even
the most basic properties, for example the equilibrium crystal
structure, is extremely difficult to calculate.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
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| User: "Greg Hansen" |
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| Title: Re: Physics of Settling? |
27 Aug 2006 10:13:10 AM |
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wrote:
In article <44F05B71.1060102@tcq.net>, Greg Hansen <glhansen@tcq.net> wrote:
wrote:
In article <eck8q7$1d9$2@eeyore.INS.cwru.edu>,
Andy Resnick <andy.resnick@op.case.edu> wrote:
I thought about the paint mixing yesterday. Another thing to try,
but I can't figure out how, is to "see" if the different colors
mix differently (I'm not writing this well). I noticed that
coffee can covers that were dyed were much more difficult for
my hands to pry off than the white lids. My hypothese was that
the color created more stiffness but had no way to verify.
The color doesn't determine the properties, although it reflects them.
The lid was colored by adding stuff to it. Possibly including titanium
dioxide powder for opacity. Plasticine clay loaded with BBs is stiffer
than plasticine clay without, and I'd expect plastic loaded with powder
is stiff than plastic without.
Thank you :-). [emoticon checks off another mystery of life]
Stupid question: Would round balls, where stiffness isn't part
of the dynamic, behave differently if they were different colors?
Would stiffness not be part of the dynamic?
Mechanics doesn't care what color a particle is. Mechanics cares about
things like stiffness, density, and friction. It's possible that
different colored balls would behave differently, but that would be
because they have different mechanical properties. Maybe because
they're made of different materials, and maybe because of additives.
At least, that seems like a reasonable hypothesis. Effects strictly of
color would be on the order of (E_lambda_1 - E_lambda_2)/c.
We used to figure all this out when we were kids. :-) We just
couldn't put the math to it.
/BAH
Kids usually have more free time, too.
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| User: "Weatherlawyer" |
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| Title: Re: Physics of Settling? |
27 Aug 2006 12:59:21 PM |
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Greg Hansen wrote:
Mechanics doesn't care what color a particle is. Mechanics cares about
things like stiffness, density, and friction. It's possible that
different colored balls would behave differently, but that would be
because they have different mechanical properties. Maybe because
they're made of different materials, and maybe because of additives.
At least, that seems like a reasonable hypothesis. Effects strictly of
color would be on the order of (E_lambda_1 - E_lambda_2)/c.
Actually in a controlled environment the temperature is going to rule
the colours inconsequential but in real life the colour would have the
most effect on the temperature.
Try getting out more:
"The researchers initially considered a system of same-size particles,
and equated the kinetic energy of each particle, which is directly
related to the ambient temperature in kinetic theory, to its equivalent
potential energy.
They found that a critical temperature exists below which a layer of
particles 'condenses out' at the bottom of the vessel. This critical
temperature corresponds to a particular ratio of mass and diameter."
http://physicsweb.org/articles/news/5/4/5
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| User: "" |
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| Title: Re: Physics of Settling? |
28 Aug 2006 04:13:23 AM |
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In article <1156701561.475442.291750@m73g2000cwd.googlegroups.com>,
"Weatherlawyer" <Weatherlawyer@hotmail.com> wrote:
Greg Hansen wrote:
Mechanics doesn't care what color a particle is. Mechanics cares about
things like stiffness, density, and friction. It's possible that
different colored balls would behave differently, but that would be
because they have different mechanical properties. Maybe because
they're made of different materials, and maybe because of additives.
At least, that seems like a reasonable hypothesis. Effects strictly of
color would be on the order of (E_lambda_1 - E_lambda_2)/c.
Actually in a controlled environment the temperature is going to rule
the colours inconsequential but in real life the colour would have the
most effect on the temperature.
Try getting out more:
There is some snot on your nose. If people don't ask questions,
they won't learn. The only reason science has advanced is because
people notice stuff and wonder.
<snip>
/BAH
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| User: "Greg Hansen" |
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| Title: Re: Physics of Settling? |
27 Aug 2006 09:31:23 PM |
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Weatherlawyer wrote:
Greg Hansen wrote:
Mechanics doesn't care what color a particle is. Mechanics cares about
things like stiffness, density, and friction. It's possible that
different colored balls would behave differently, but that would be
because they have different mechanical properties. Maybe because
they're made of different materials, and maybe because of additives.
At least, that seems like a reasonable hypothesis. Effects strictly of
color would be on the order of (E_lambda_1 - E_lambda_2)/c.
Actually in a controlled environment the temperature is going to rule
the colours inconsequential but in real life the colour would have the
most effect on the temperature.
Try getting out more:
"The researchers initially considered a system of same-size particles,
and equated the kinetic energy of each particle, which is directly
related to the ambient temperature in kinetic theory, to its equivalent
potential energy.
They found that a critical temperature exists below which a layer of
particles 'condenses out' at the bottom of the vessel. This critical
temperature corresponds to a particular ratio of mass and diameter."
http://physicsweb.org/articles/news/5/4/5
Oh, good. A clickable link. I can get out without prying my butt from
the chair.
The article didn't seem to suggest that color would have much of an
effect in real life or the lab, though. Temperature differences caused
by radiant heating would pretty much be thermalized by conduction and
convection through the mass of all those small particles in thermal
contact, although the temperature discussed in that article is more of
an analogy, as if the macroscopic spheres were atoms in kinetic theory.
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| User: "John Bailey" |
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| Title: Re: Physics of Settling? |
22 Aug 2006 06:34:12 AM |
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On 21 Aug 2006 20:16:58 -0700, "Cliff" <hcbowman@gmail.com> wrote:
I observed a phenomenon today I'd like to know more about.
Unfortunately, I don't even know the search terms to use, so any
pointers about where I should start reading would be very appreciated!
Clearly I don't really understand what's going on with settling. I'd
like to learn a little about how to quantify "ease of separating" the
spheres through settling and what factors influence the phenomenon.
http://en.wikipedia.org/wiki/Brazil_nut_effect
Also: cond-mat/0402256
Google with the terms: Brazil Nut effect. Shinbrot as a term will
narrow the search. Apparently at least three effects compete in the
settling process and various experiments produce conflicting results.
"Shaken, not stirred...." Fleming
John
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| User: "Cliff" |
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| Title: Re: Physics of Settling? |
22 Aug 2006 02:51:37 PM |
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Replying to my own post. How egotistical is that? :-)
I now remember attending a departmental lecture many years ago about
"food engineering." The speaker had worked on a variety of really
unusual projects, including one to keep the marshmallows from settling
out in a box of Lucky Charms. General Mills had contracted his firm to
figure out how to make the sugary marshmallows (which tended to be
denser) from separating from the oat-based cereal.
Unfortunately, he didn't get into the physics of settling in a cereal
box.
--Cliff
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