Never weigh a hot object?
Craig Mitchell
I am a lowly, freshman chem student. So this may sound stupid but in
my text book I'm told: "Never weigh an object when it is still hot.
Wait until it cools to room temperature." Why is this?
Thanks, Craig M.
Alan "Uncle Al" Schwartz
Convective air currents wafting by the hot object will levitate it
somewhat. This is a measurable problem with pan balances.
The hot object on a load cell will re rather less affected by convection
(it isn't suspended in mid-air), but the temperature change will alter
how the load cell responds - dimensions, magnetic field, and electrical
resistance.
Also remember that hot air has a lower density than ambient air, and your
object is weighed while displacing air - altered boyancy effects.
A better summary might be, "Weigh it reproducibly if you want precision."
If you have precision you can get accuracy.
--
Alan "Uncle Al" Schwartz
Uncl...@ix.netcom.com ("zero" before @)
http://www.netprophet.co.nz/uncleal/ (best of + new)
http://www.ultra.net.au/~wisby/uncleal.htm (lots of + new)
(Toxic URLs! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!
William Wu
Craig Mitchell (cpm...@ix.netcom.com) wrote:
: I am a lowly, freshman chem student. So this may sound stupid but in
: my text book I'm told: "Never weigh an object when it is still hot.
: Wait until it cools to room temperature." Why is this?
Cause the heat of the object your weighing will create air currents
(updraft) and through off your mesuerments. This will effect both the old
mechancal and newer digital meters.
Lloyd R. Parker
Craig Mitchell (cpm...@ix.netcom.com) wrote:
: I am a lowly, freshman chem student. So this may sound stupid but in
: my text book I'm told: "Never weigh an object when it is still hot.
: Wait until it cools to room temperature." Why is this?
: Thanks, Craig M.
A student of mine once answered, "the atoms are all still jumping around."
That's not it, of course. Think about what the hot object will do to the
air around it, and what the warm air will do to the balance pan.
Travis & Kyla Woodward
because there are minor convection currents around
hot objects that flow upward
the object will appear to weigh less
Craig Mitchell <cpm...@ix.netcom.com> wrote in article
<51iav6$k...@dfw-ixnews9.ix.netcom.com>...
Library Patron
cpm...@ix.netcom.com(Craig Mitchell ) wrote:
>I am a lowly, freshman chem student. So this may sound stupid but in
>my text book I'm told: "Never weigh an object when it is still hot.
>Wait until it cools to room temperature." Why is this?
>
> Thanks, Craig M.
Marko....@guest.arnes.si
Library Patron <pat...@public.lib.ga.us> wrote:
because air moisture can condense while cooling, or to avoid damage
the ballance
mj
Alan "Uncle Al" Schwartz
...and people scoff when I decry "zero-goal" education!
Ross Frisbie
Alan \"Uncle Al\" Schwartz (uncl...@ix.netcom.com) wrote:
: ...and people scoff when I decry "zero-goal" education!
: Alan "Uncle Al" Schwartz
Not all of us, but unfortunatly, not enough of us.
I have no idea how good my usenet feed is, so maybe they already exist,
but shouldn't there be a
sci.chem.questions-I-don't-want-to-look-up-in-my-book-myself-because-that-
takes-more-work-than-asking-others
or a
sci.chem.i-am-trying-to-synthesize-controlled-substances-but-know-
diddley-about-chemistry
to harmlessly shunt off many of these questions?
Or perhaps, Uncle Al, you could be guru and chief debunker in
sci.chem.zero-goal-education?
Ross
salane king
Consider why a hot air baloon rises, then you will know why.
John ross
In article <51nb9a$7...@news-read-1.PeachNet.EDU>, Library Patron <pat...@public.lib.ga.us> says:
>
>cpm...@ix.netcom.com(Craig Mitchell ) wrote:
>>I am a lowly, freshman chem student. So this may sound stupid but in
>>my text book I'm told: "Never weigh an object when it is still hot.
>>Wait until it cools to room temperature." Why is this?
>>
>> Thanks, Craig M.
may through off a volume reading and thus through off a density calculation
Confusious say:
Also, Hot objects burn lowly freshman chem student's hands far easier than
cool objects!
john
R. Bailey
Library Patron <pat...@public.lib.ga.us> wrote:
>cpm...@ix.netcom.com(Craig Mitchell ) wrote:
>>I am a lowly, freshman chem student. So this may sound stupid but in
>>my text book I'm told: "Never weigh an object when it is still hot.
>>Wait until it cools to room temperature." Why is this?
>>
>> Thanks, Craig M.
>
>
pan will rise.
2. Bouyancy if the shape of the object permits it to hold a volume of air
not at the temperature of its surroundings.
Check out an OLD analytical chemistry book where all the tricks for
making accurate measurements are given.
Coen Gronert
Alan "Uncle Al" Schwartz wrote:
>
> Marko....@guest.arnes.si wrote:
> >Library Patron <pat...@public.lib.ga.us> wrote:
> >
> >>cpm...@ix.netcom.com(Craig Mitchell ) wrote:
> >>>I am a lowly, freshman chem student. So this may sound stupid but in
> >>>my text book I'm told: "Never weigh an object when it is still hot.
> >>>Wait until it cools to room temperature." Why is this?
> >>>
> >>> Thanks, Craig M.
> >>because it will weigh more than when at room temp.
> >
> >the ballance
> >
> >mj
>
>
> Alan "Uncle Al" Schwartz
> Uncl...@ix.netcom.com ("zero" before @)
> http://www.netprophet.co.nz/uncleal/ (best of + new)
> http://www.ultra.net.au/~wisby/uncleal.htm (lots of + new)
> (Toxic URLs! Unsafe for children, Democrats, and most mammals)
> "Quis custodiet ipsos custodes?" The Net!
We discussed over here that due to E= m.c^2 the mass thus weight
increases with a rising internal energy hence higher temperature.
Where do we go wrong?
Pardon my English.
Coen
John ross
>>>>I am a lowly, freshman chem student. So this may sound stupid but in
>>>>my text book I'm told: "Never weigh an object when it is still hot.
>>>>Wait until it cools to room temperature." Why is this?
>>>>
>>>> Thanks, Craig M.
>>
>>because air moisture can condense while cooling, (snip)
Popycock!!!!
Air moisture will only condense on an object which is cooler than the air!!!
We are talking about a hot object!
john
John ross
>We discussed over here that due to E= m.c^2 the mass thus weight
>increases with a rising internal energy hence higher temperature.
>Where do we go wrong?
>Pardon my English.
>
>Coen
I swear, some people cannot tell the differences between mass, energy,
temperature, density and their arses
Mass is mass... period!
temperature has no bearing on the mass, but it does effect how fast its molecules
are moving around. This in turn affects its energy (E = mc^2), as well as its volume.
If you put an object on an accurate scale and weigh it hot, ambient, or cold( allowing for
any atmosperic condensation) the scale will give the same reading!!
Since the volume can change, this could affect a density calculation, but not its weight.
The only real concerns about weighing a hot object are safty to the operator and the
scale
opinions welcome..
john ro...@mk.com
Stachov
1. You might burn yourself or some other piece of laboratory equipment.
2. If you are concerned about accurate results, the convection currents
from heated air rising around the object could disturb the weighing.
3. If the object is not very dense but has a high coefficient of thermal
expansion the effects of air bouyancy might be significant? (just
speculating)
Coen Gronert
John ross wrote:
>
> In article <3240FA...@euronet.nl>, Coen Gronert <cg...@euronet.nl> says:
>
> >We discussed over here that due to E= m.c^2 the mass thus weight
> >increases with a rising internal energy hence higher temperature.
> >Where do we go wrong?
> >Pardon my English.
> >
> >Coen
>
> I swear, some people cannot tell the differences between mass, energy,
> temperature, density and their arses
I always thought internet to be a friendly crowd.
>
> Mass is mass... period!
> temperature has no bearing on the mass, but it does effect how fast its molecules
> are moving around. This in turn affects its energy (E = mc^2), as well as its volume.
I do bot understand. If the energy increase and light velocity is constant ht
emass should increase isn't it?
> If you put an object on an accurate scale and weigh it hot, ambient, or cold( allowing for
> any atmosperic condensation) the scale will give the same reading!!
> Since the volume can change, this could affect a density calculation, but not its weight.
>
> The only real concerns about weighing a hot object are safty to the operator and the
> scale
> You did not answer my question.
> opinions welcome..
>
> john ro...@mk.com
Can you be more exact in your opinions?
Coen
Tim Blackmore
In article <51rb8u$a...@esgadm.esg.mk.com>, john...@mk.com (John ross) wrote:
>In article <3240FA...@euronet.nl>, Coen Gronert <cg...@euronet.nl> says:
>
>>We discussed over here that due to E= m.c^2 the mass thus weight
>>increases with a rising internal energy hence higher temperature.
>>Where do we go wrong?
>>Pardon my English.
>>
>>Coen
>
>I swear, some people cannot tell the differences between mass, energy,
>temperature, density and their arses
>
>temperature has no bearing on the mass, but it does effect how fast its
molecules
>are moving around. This in turn affects its energy (E = mc^2), as well as
its volume.
allowing for
>any atmosperic condensation) the scale will give the same reading!!
>Since the volume can change, this could affect a density calculation, but not
its weight.
>
>The only real concerns about weighing a hot object are safty to the operator
and the
>scale
>
It will indeed give exactly the same reading. As long as you are working in a
vacuum. The hot object will heat up the air around it. This will affect the
buoyancy on the object while reference weights inside the balance will still
be at room temperature and will not compensate for this effect.
Tim Blackmore tim_bl...@notes.ipl.ca
John ross
The energy of >one billion grams< of TNT >detonating< weighs
>44.5 mg.
>
I'm sorry i thought we we considering weighing a hot vs cold object!!!!!
not a substance undergoing chemical reaction, energy release, and possible
phase change!!
Why can't you people understand that mass doesn't change with temperature;
the gravitational constant is constant; weight does not change!!!
I don't care about "slight convectional currents due to heated air; any decent
scale is shielded from wind and typical lab equipment (beakers, watchglasses)
are heavy enough to completly ignore any false readings from negligable
heat currents
This discussion is amazing!!
also; what sort of flawed logic dictates that 1 billion grams = 44.5 mg????
dosn't anybody think rationally anymore??
john
Alan "Uncle Al" Schwartz
Coen Gronert <cg...@euronet.nl> wrote:
>Alan "Uncle Al" Schwartz wrote:
>>
>> Marko....@guest.arnes.si wrote:
>> >Library Patron <pat...@public.lib.ga.us> wrote:
>> >
>> >>cpm...@ix.netcom.com(Craig Mitchell ) wrote:
>> >>>my text book I'm told: "Never weigh an object when it is still hot.
>> >>>Wait until it cools to room temperature." Why is this?
>> >>>
>> >>> Thanks, Craig M.
>> >
>> >because air moisture can condense while cooling, or to avoid damage
>> >the ballance
>> >
>> >mj
>>
>> ...and people scoff when I decry "zero-goal" education!
>>
>> --
>> Alan "Uncle Al" Schwartz
>> Uncl...@ix.netcom.com ("zero" before @)
>> http://www.netprophet.co.nz/uncleal/ (best of + new)
>> http://www.ultra.net.au/~wisby/uncleal.htm (lots of + new)
>> (Toxic URLs! Unsafe for children, Democrats, and most mammals)
>> "Quis custodiet ipsos custodes?" The Net!
>
>increases with a rising internal energy hence higher temperature.
>Where do we go wrong?
>Pardon my English.
Assume the object is at 400 C vs 20 C. What is the E=mc^2 weight
difference?
Hint: The energy of >one billion grams< of TNT >detonating< weighs
44.5 mg.
--
Lloyd R. Parker
John ross (john...@mk.com) wrote:
: I don't care about "slight convectional currents due to heated air; any decent
: are heavy enough to completly ignore any false readings from negligable
: heat currents
Not when balances weigh to the nearest mg or even smaller. It doesn't
matter how heavy the object is; convection currents due to warmed air can
make a difference on a sensitive balance.
:
: This discussion is amazing!!
:
: also; what sort of flawed logic dictates that 1 billion grams = 44.5 mg????
What Al meant was that 1 billion tons of TNT going off would make a
difference of 44.5 mg in the mass of the products -- the energy released
would be such that 44.5 mg of mass would be converted to the energy.
Whenever energy is absorbed or released, the mass changes. Mass is
basically just nature's way of storing energy. Except for nuclear
reactions, though, the mass change is small enough to neglect.
John Cranmer
Alan \"Uncle Al\" Schwartz <uncl...@ix.netcom.com> wrote:
>>We discussed over here that due to E= m.c^2 the mass thus weight
>>increases with a rising internal energy hence higher temperature.
>>Where do we go wrong?
>>Pardon my English.
>Assume the object is at 400 C vs 20 C. What is the E=mc^2 weight
>difference?
>Hint: The energy of >one billion grams< of TNT >detonating< weighs
>44.5 mg.
I thought it was to stop your fingers getting burnt
John
:
We are born naked, wet and hungry. Then it gets worse.
Jeffrey Bodwin
On 19 Sep 1996, John ross wrote:
> The energy of >one billion grams< of TNT >detonating< weighs
> >44.5 mg.
> >
>
> not a substance undergoing chemical reaction, energy release, and possible
> phase change!!
>
> Why can't you people understand that mass doesn't change with temperature;
> the gravitational constant is constant; weight does not change!!!
>
> scale is shielded from wind and typical lab equipment (beakers, watchglasses)
> are heavy enough to completly ignore any false readings from negligable
> heat currents
Before you make even more of an ass of yourself than you already have, do
the experiment. Any decent BALANCE {you're not in the bathroom} will be
shielded from outside currents which will place the object in question
(like a crucible) in an enclosed space, creating air currents inside the
enclosure. Also, any decent BALANCE will weigh to, at the very least,
milligram accuracy and it doesn't take much of a breeze to kick up a few
milligrams. Like the answer or not, take a crucible, heat it until it's
glowing hot, place it on what you consider to be a "decent scale". If the
"decent scale" is worth its weight, you will see the temerature fluctuate.
Oh, and by the way, don't touch the crucible when it's glowing hot.
-------------------------------**-------------------------------
| Jeffrey J. Bodwin I consider myself a pretty good judge |
| bodw...@umich.edu of people. That's why I don't |
| Just me, not you, not UM. like none of them.-Roseanne |
~~~~~~~~~~**~~~~~~~~~**~~~~~~~~~**~~~~~~~~~**~~~~~~~~~**~~~~~~~~~~
Chris Miles
> Why can't you people understand that mass doesn't change with temperature;
> the gravitational constant is constant; weight does not change!!!
You are right in that mass does not change, but you are wrong about
weight. Weight is a measure of the total forces acting on the object being
weighed (so that, for example, the buoyancy of the air is a factor during
weighing) and so weight can change even when the mass of the weighed
object does not. Weigh a full cylinder of helium plus a large empty
balloon. Now empty the cylinder into the ballon and reweigh them. The
total mass of the two hasn't changed, but the total weight in the second
instance (the filled balloon) may well be less than zero due to the
buoyancy of the air.
> I don't care about "slight convectional currents due to heated air; any
decent
> scale is shielded from wind and typical lab equipment (beakers, watchglasses)
> are heavy enough to completly ignore any false readings from negligable
> heat currents
If you have tried weighing a warm object on a good balance you will find
that this is not so. I saw a good demonstration with a glass vial weighed
on a balance that reads to 0.0001 grams. After the vial had been held in
the hand for half a minute it was reweighed and was several milligrams
lighter due to the thermally-induced air currents.
> This discussion is amazing!!
> john
Chris Miles
---------------------------------------------------------------------
Disclaimer: The above is a personal opinion and does not reflect the
official view of AgResearch Ltd.
---------------------------------------------------------------------
H. Wayne Richardson
On Thu, 19 Sep 96 14:03:00 GMT, tim_bl...@notes.ipl.ca (Tim
Blackmore) wrote:
>In article <51rb8u$a...@esgadm.esg.mk.com>, john...@mk.com (John ross) wrote:
>>In article <3240FA...@euronet.nl>, Coen Gronert <cg...@euronet.nl> says:
>>
>>If you put an object on an accurate scale and weigh it hot, ambient, or cold(
>allowing for
>>any atmosperic condensation) the scale will give the same reading!!
>>Since the volume can change, this could affect a density calculation, but not
>its weight.
>>
>>The only real concerns about weighing a hot object are safty to the operator
>and the
>>scale
>>
>
>It will indeed give exactly the same reading. As long as you are working in a
>vacuum. The hot object will heat up the air around it. This will affect the
>buoyancy on the object while reference weights inside the balance will still
>be at room temperature and will not compensate for this effect.
>
>Tim Blackmore tim_bl...@notes.ipl.ca
Can't I just heat the balance to the temperature of the object to be
weighed? Will it weigh more or less? And what about Naomi?
Wayne?
Dave Whitman
john...@mk.com (John ross) wrote:
>>>because air moisture can condense while cooling, (snip)
>Popycock!!!!
>Air moisture will only condense on an object which is cooler than the air!!!
>We are talking about a hot object!
>john
Poppycock yourself. Try this experiment:
Put some activated charcoal in a crucible. Heat overnight at 300C.
Take out of the oven while hot and weigh it on an analytical balance
(accurate to 0.0001 g).
Although you'll have trouble getting an accurate reading due to the
convection currents around the crucible in the weighing chamber,
you'll have no trouble watching the weight go up as moisture adsorbs
onto the carbon.
---
Dave Whitman "The opinions expressed are those
Rohm and Haas Company of the author, not Rohm and Haas."
dwhi...@rohmhaas.com They made me say that. Really.
Eric Lucas
Tim Blackmore wrote:
>
> In article <51rb8u$a...@esgadm.esg.mk.com>, john...@mk.com (John ross) wrote:
> >In article <3240FA...@euronet.nl>, Coen Gronert <cg...@euronet.nl> says:
> >
> >>increases with a rising internal energy hence higher temperature.
> >>Where do we go wrong?
> >>Pardon my English.
> >>
> >
> >I swear, some people cannot tell the differences between mass, energy,
> >temperature, density and their arses
> >
> >Mass is mass... period!
> >temperature has no bearing on the mass, but it does effect how fast its
> molecules
> >are moving around. This in turn affects its energy (E = mc^2), as well as
> its volume.
> allowing for
> >any atmosperic condensation) the scale will give the same reading!!
> >Since the volume can change, this could affect a density calculation, but not
> its weight.
> >
> >The only real concerns about weighing a hot object are safty to the operator
> and the
> >scale
> >
>
> It will indeed give exactly the same reading.
In all practical terms, yes, but the poster above was wrong. Special
relativity does indeed predict that the object will have greater mass at
a higher temperature. It's just that this difference will be well
beyond the precision of even the most precise methods to measure mass.
E=mc^2 (or rather the differential form, delta(E) = delta(m)*c^2) tells
you just exactly how much the mass difference is, in terms of the energy
difference, which can be calculated from the temperature difference and
the heat capacity of the material. Trickiest part is to figure out the
correct units involved.
In one sense, he was right--some people don't know mass, energy, density
or temperature from their arse. That's because special relativity tells
us that these are all *exactly* the same thing--mass *is* energy.
Density is mass per volume, and is therefore energy per volume.
Temperature represents thermal energy, which is mass. And, last time I
checked, my arse has mass (never you mind exactly how much) and is
therefore energy.
Eric Lucas
Eric Lucas
Dave Whitman wrote:
>
> john...@mk.com (John ross) wrote:
>
> >>>because air moisture can condense while cooling, (snip)
>
> >Popycock!!!!
>
> >Air moisture will only condense on an object which is cooler than the air!!!
> >We are talking about a hot object!
> >john
>
> Poppycock yourself. Try this experiment:
>
> Put some activated charcoal in a crucible. Heat overnight at 300C.
> Take out of the oven while hot and weigh it on an analytical balance
> (accurate to 0.0001 g).
>
> Although you'll have trouble getting an accurate reading due to the
> convection currents around the crucible in the weighing chamber,
> you'll have no trouble watching the weight go up as moisture adsorbs
> onto the carbon.
Poppycock *yourself*. That's not condensation, that's chemisorption of
water on the activated carbon surface. Two different phenomena, one of
which is a physical phenomenon and the other of which is a chemical
phenomenon that is specific to a certain set of materials. Although,
admittedly, a lot of different materials may chemisorb water when they
are activated at a sufficiently high temperature.
Eric Lucas
Eric Lucas
Jeffrey Bodwin wrote:
>
> On 19 Sep 1996, John ross wrote:
> > The energy of >one billion grams< of TNT >detonating< weighs
> > >44.5 mg.
> > >
> >
> > I'm sorry i thought we we considering weighing a hot vs cold object!!!!!
> > not a substance undergoing chemical reaction, energy release, and possible
> > phase change!!
> >
> > the gravitational constant is constant; weight does not change!!!
> >
> > scale is shielded from wind and typical lab equipment (beakers, watchglasses)
> > are heavy enough to completly ignore any false readings from negligable
> > heat currents
> Before you make even more of an ass of yourself than you already have,
I agree! This guy has absolutely no understanding of relativity, nor
has he ever done any work in a chemistry laboratory, apparently.
> Oh, and by the way, don't touch the crucible when it's glowing hot.
I'll never forget the time when I was in high school that the smartest
kid in chemistry class heated a crucible to glowing and turned off the
Bunsen burner. I think you see where this is going.... I turned around
and was doing something else a few seconds later when I heard a very
loud scream, and the sound of a crucible smashing on the floor. His
excuse was "well, it wasn't glowing anymore, so I didn't think it was
hot." This is the same guy that put his goggles on upside down and left
them that way for the whole class period. At the end, he complained to
the teacher that his goggles hurt his nose and that they didn't fit
right. All brains, no common sense!
Eric Lucas
the man
On 19 Sep 1996 21:41:55 GMT, mil...@agresearch.cri.nz (Chris Miles)
wrote:
SNIP
>
>> I don't care about "slight convectional currents due to heated air; any
>decent
>> scale is shielded from wind and typical lab equipment (beakers, watchglasses)
>> are heavy enough to completly ignore any false readings from negligable
>> heat currents
>
>If you have tried weighing a warm object on a good balance you will find
>that this is not so. I saw a good demonstration with a glass vial weighed
>on a balance that reads to 0.0001 grams. After the vial had been held in
>the hand for half a minute it was reweighed and was several milligrams
>lighter due to the thermally-induced air currents.
>
>
since at least some of you don't have a clue about this simple
question:
a balance weighs everything over the pan, relative to everything under
the pan. If the air over the pan is heated, and the air under the pan
is not, the pan will weigh less!!!!!!!
it doesn't get any simpler.
Thallion
sk> From: salane king <sk...@pediatrics.uams.edu>
sk> Consider why a hot air baloon rises, then you will know why.
Duh? As long as he is not weighing a gas, this will be of NO importance.
//Thallion
-+- OLMS 2.5p UNREG
-+- OLMS 2.5p UNRE
the man
On 18 Sep 1996 15:19:59 GMT, john...@mk.com (John ross) wrote:
>In article <51nb9a$7...@news-read-1.PeachNet.EDU>, Library Patron <pat...@public.lib.ga.us> says:
>>
>>cpm...@ix.netcom.com(Craig Mitchell ) wrote:
>>>I am a lowly, freshman chem student. So this may sound stupid but in
>>>my text book I'm told: "Never weigh an object when it is still hot.
>>>Wait until it cools to room temperature." Why is this?
>>>
>>> Thanks, Craig M.
>The temperature of the object should not affect the weight of the object, but it
>may through off a volume reading and thus through off a density calculation
>Confusious say:
>Also, Hot objects burn lowly freshman chem student's hands far easier than
>cool objects!
>
>john
let's see. the density of air at room temp is about 30 grams per mole,
and 24.45 moles per liter. that comes to 1.23 milligrams per
milliliter.
the density of air at 25 C is 1.25 times the density of air at 100 C.
373 K / 298 K = 1.25
now, we can eaily see that the mass of 1 ml of air at 100 C is 0.31 mg
less than 1 ml of air at room temp.
conclusion: the weight of air setting on top of the balance pan is
lighter than the weight of air setting on top of the counter balances
(in the weighing mechanisms) when the balance pan has a hot object on
it.
IF THAT'S NOT SIMPLIFIED ENOUGH FOR A BUNCH OF CHEMISTS, THEN YOU
SHOULD ALL GO BACK TO HIGH SCHOOL!!!!!
the man
Reposting article removed by rogue canceller.
Ian Woollard
In article <51rtcn$a...@esgadm.esg.mk.com>, John ross <john...@mk.com> wrote:
> The energy of >one billion grams< of TNT >detonating< weighs
>>44.5 mg.
>>
>
>I'm sorry i thought we we considering weighing a hot vs cold object!!!!!
>not a substance undergoing chemical reaction, energy release, and possible
>phase change!!
>
>Why can't you people understand that mass doesn't change with temperature;
>the gravitational constant is constant; weight does not change!!!
According to Special Theory of Relativity the mass of an object DOES
change as you heat it. Hence the object weighs more. But the effect is
very, very, very tiny.
The increased mass is:
E/C^2
- because C is 3*10-8, the added mass is indetectable with a
scale. However experiments with subatomic particles like electrons
show that the increased mass is real.
>I don't care about "slight convectional currents due to heated air; any decent
>scale is shielded from wind and typical lab equipment (beakers, watchglasses)
>are heavy enough to completly ignore any false readings from negligable
>heat currents
Perhaps, but don't bet on it.
>This discussion is amazing!!
>
>also; what sort of flawed logic dictates that 1 billion grams = 44.5 mg????
That would be 1 billion grams of *TNT* and that would be a military
definition... ;-)
>dosn't anybody think rationally anymore??
Always. But where you end up depends on what axioms you start with.
>john
--
-Ian (wo...@nortel.co.uk)
A day for firm decisions| Predestination was | Put off procrastination
Or is it? | doomed from the start | as long as possible.
Gary Dyrkacz
"R. Bailey" <bai...@rpi.edu> wrote:
>Library Patron <pat...@public.lib.ga.us> wrote:
>>cpm...@ix.netcom.com(Craig Mitchell ) wrote:
>>>I am a lowly, freshman chem student. So this may sound stupid but in
>>>my text book I'm told: "Never weigh an object when it is still hot.
>>>Wait until it cools to room temperature." Why is this?
>>>
>>> Thanks, Craig M.
>>because it will weigh more than when at room temp.
>>
>>
>1. Convection currents - air around the hot object and the balance
>pan will rise.
>2. Bouyancy if the shape of the object permits it to hold a volume of air
>not at the temperature of its surroundings.
>Check out an OLD analytical chemistry book where all the tricks for
>making accurate measurements are given.
So I gather the new books don't talk about this? The above reasons
were the ones I was taught from both the "old" analtycial chemistry
books and drummed into me by my anaytical chemistry teachers Was this
a surprise to many people?
[rant mode on]
While were on balances, and books: I hope the new texts do a better
job discussing issues such as wieghing very dry materials on those
modern wonders, the electronic analytical balance. We have both a
modern 5 place electronic balance and an electronic microbalance. We
often have to weigh dry organic powders, and especially for accurate
weights on small amounts we resort to our ancient knife edge single
beam models to get accurate weights. The electronic balances and
especially our microbalance turn out to be a great device to measure
static charges. Oh yes, we know about static eliminator counter tops,
alpha sources and special anti-static pan configurations. They help
but none work real well. If you want to experience this for yourself
try drying a Nucleopore membrane filter at say 60 C then weigh it.
I wonder what will happen when all the old knife balances have finally
gone the way of the rubber stoppered flask?
[rant mode off]
Opinions and rants reflect the author's views not his workplace.
Gary Dyrkacz
Argonne National Laboratory
dyr...@anlchm.chm.anl.gov
Tim Blackmore
In article <51rtcn$a...@esgadm.esg.mk.com>, john...@mk.com (John ross) wrote:
> The energy of >one billion grams< of TNT >detonating< weighs
>>44.5 mg.
>>
>
>I'm sorry i thought we we considering weighing a hot vs cold object!!!!!
>not a substance undergoing chemical reaction, energy release, and possible
>phase change!!
>
>Why can't you people understand that mass doesn't change with temperature;
>the gravitational constant is constant; weight does not change!!!
>
decent
>scale is shielded from wind and typical lab equipment (beakers, watchglasses)
>are heavy enough to completly ignore any false readings from negligable
>heat currents
>
>
>also; what sort of flawed logic dictates that 1 billion grams = 44.5 mg????
>
>
Clueless. Truely clueless.
Tim Blackmore tim_bl...@notes.ipl.ca
Richard J. Bucek
tick...@europa.com (the man) wrote:
>On 19 Sep 1996 21:41:55 GMT, mil...@agresearch.cri.nz (Chris Miles)
>wrote:
>SNIP
>>
>>> I don't care about "slight convectional currents due to heated air; any
>>decent
>>> scale is shielded from wind and typical lab equipment (beakers, watchglasses)
>>> are heavy enough to completly ignore any false readings from negligable
>>> heat currents
>>
>>If you have tried weighing a warm object on a good balance you will find
>>that this is not so. I saw a good demonstration with a glass vial weighed
>>on a balance that reads to 0.0001 grams. After the vial had been held in
>>the hand for half a minute it was reweighed and was several milligrams
>>lighter due to the thermally-induced air currents.
>>
>>
>since at least some of you don't have a clue about this simple
>question:
>a balance weighs everything over the pan, relative to everything under
>the pan. If the air over the pan is heated, and the air under the pan
>is not, the pan will weigh less!!!!!!!
>it doesn't get any simpler.
There is another factor, that from my experience, could affect the
perceived weight of an object. That is the charge that can build up
on a weighing vessal, when placed on an analytical balance enclosed in
glass!!!! This is known as the "Capacitor Effect" distorting
critical weighings.
Joe Bramblett
On 16 Sep 1996 10:39:09 -0400, lpa...@larry.cc.emory.edu (Lloyd R. Parker)
wrote:
>A student of mine once answered, "the atoms are all still jumping around."
>
>That's not it, of course. Think about what the hot object will do to the
>air around it, and what the warm air will do to the balance pan.
>
Also, some scales aren't particularly receptive to hot objects. Consider that a
lot of freshman students are less than cautious about these sort of things, and
that dropping that still-glowing crucible onto the metal pan with the plastic
support isn't a very good way to treat precision equipment.
Joe Bramblett
airnews...@airmail.net
Internet America
Airnews Project Manager
http://www.airnews.net
Scott Sutherland
In a reply to an article on weighing hot objects, "Ross
Frisbie" puts down people who submit questions to
U
Scott Sutherland
In a reply to an article on weighing hot objects, "Ross
don't-want-to-look-up-in-my-book-myself-because...'.
This implies that people who look for information on the
USENET are lazy. I disagree. When looking for a solution
to a particular problem, or the answer to a question, it
makes perfect sense to use all of the resources at your
disposal. My training as a Ph.D. in chemistry exposed me
to many resources for information, including text books,
Beilstein, Chem Abstracts, on-line searching, conversations
with other scientists (in person and on the phone),and my own
brain (deriving equations and coming up with solutions,
that is ;^)
ALL of these are valid approaches to getting information.
There is no "correct order" in which to use these resources.
Now that the INTERNET is so easily accessed, and
encyclopedias come on CD-ROM, why NOT use them to their fullest
potential. As a grad student (1985-90), I had access to the
Internet and found it an INVALUABLE resource. Access to
thousands of scientists worldwide! I agree that students need
to use ALL of their resources, but don't label them LAZY for
using any ONE of them.
IMHO, Scott Sutherland 10267...@compuserve.com
Jeroen BELLEMAN
In article <526b1g$a...@milo.mcs.anl.gov>,
Gary Dyrkacz <dyr...@anlchm.chm.anl.gov> wrote:
>We often have to weigh dry organic powders, and especially for accurate
>weights on small amounts we resort to our ancient knife edge single
>beam models to get accurate weights. The electronic balances and
>especially our microbalance turn out to be a great device to measure
>static charges.
That's interesting. What is it that makes electronic balances so
much more sensitive to static charges? At first sight I'd say there
may be a serious design error in there.
Jeroen Belleman
jeroen....@cern.ch
Triple Quadrophenic
In article <52799e$o9m$4...@mhafn.production.compuserve.com>,
10267...@CompuServe.COM (Scott Sutherland) says...
There are several reasons why I don't agree with handing out answers to
obvious homework questions without making them do some work on the answer.
A good teacher will set a homework question that requires the student to
understand a process/technique to reach the correct answer. If somebody on
the net just hands out the correct answers then the only person to benefit
is the person who posted the answer (boosted ego). The student is allowed to
progress through their course whilst an important concept is alien to them.
Sooner or later this fact will be exposed, normally in an exam when it's too
late to do anything about it. The teacher wastes a good portion of their
time trying to teach people who don't understand anything but always get
good marks.
Morally, there is no difference between asking for the answer on the net and
copying from another student. The reasons for not doing the latter are the
same as those given above.
Any student that relies on info from the net, especially newsgroups,
deserves to fail. Who knows what sort of loon could be posting completely
wrong facts. Witness the post yeasterday where somebody said that you'd get
no adverse reaction by mixing bleach and ammonia!
Yes the net is a good resource. It's problem is that it can be too easy to
use. If a student finds that every question can be answered here then
they'll never have to use any of the other resources. Sometime they'll
advance enough (maybe) to find something that can't be answered here. Then
they're up the creek without a paddle.
Of course, you get some questions that should be answered. I've got this
problem; I've tried this and read that; I'm stuck here. Anything that
indicates that the student isn't just after the easy way out.
--
-- BEGIN NVGP SIGNATURE Version 0.000001
Frank J Hollis, Mass Spectroscopy, SmithKline Beecham, Welwyn, UK
Frank_H...@sbphrd.com or fj...@tutor.open.ac.uk
These opinions have not been passed by seven committes, eleven
sub-committees, six STP working parties and a continuous improvement
team. So there's no way they could be the opinions of my employer.
Scott Hinman
Triple Quadrophenic wrote:
> (Informed opinion deleted)
>
Well put. My feelings exactly.
Regards, Scott
William R. Penrose
In article <01bbb31d$9dd62060$d6fa...@pn92.dial.pipex.com> "Keith Wilkinson" <k.wil...@dial.pipex.com> writes:
>assertion 1
> 'shouldn't there be a
>chem.question-I-don't-want-to-look-up-in-my-book-myself-because...'.
...
>As a teacher, I welcome the idea of students putting questions on the net,
>but I think it is more appropriate to sixth form chemistry (>15yo) where
>the concepts become more stretching and require more understanding (eg:
>entropy and free energy).
Another reason for waiting until students are more advanced is that they will
have enough self-confidence to ignore the inevitable "well, you could look
this up in your textbook, if you could only read" type of answer. A sarcastic
response from some authoritative voice on the net (no names) could have
drastic effects on the embryonic enthusiasm that gets people into science in
the first place.
Bill
********************************************************
Bill Penrose, Sr. Scientist, Transducer Research,
600 North Commons Dr., Suite 117
Aurora, IL 60504, 630-978-8802, fax: -8854
NOTE: NEW AREA CODE
email wpen...@interaccess.com
********************************************************
Purveyors of contract R&D and fine gas
sensors to this and nearby galaxies.
********************************************************
Keith Wilkinson
assertion 1
'shouldn't there be a
chem.question-I-don't-want-to-look-up-in-my-book-myself-because...'.
I was very interested to read the views expressed on the question of
students putting questions up on Usenet. In the UK we are experiencing an
Internet boom but the presence of school aged students on the Internet
hasn't reached the perceived US level (yet).
As a teacher, I welcome the idea of students putting questions on the net,
but I think it is more appropriate to sixth form chemistry (>15yo) where
the concepts become more stretching and require more understanding (eg:
entropy and free energy). Below this level, assertion 1 has a certain
validity.
I enjoy answering questions that appear on this group, and I am encouraging
my students to use the Internet as a resource for two reasons.
- it enriches their ability to communicate (and I feel we have a great need
to instill that skill if we are to have good scientists)
- it enables them to get a range of good scientific responses from
academics and engineers with their own experience and perspective of the
concept. Putting such explanations together greatly enriches the students
ideas and assists understanding.
What I like about sci.chem is that there is always at least one question
that a student is able to answer or comment on. This encourages students to
explain a concept in formulating a reply, and that itself is a learning
process for them. I find it is only when one has explained a concept that
one truly understands it.
Lastly, if a student uses Usenet either to pose a question and assimilate
the replies, or else answer someone elses question, then their efforts will
be well rewarded as their confidence increases. Thus whilst I don't want
to get puritanical the greater ego trip is deservedly theirs (and why
shouldn't we get the fun out of helping them on that journey).
KRW
-------------------------------------------------------------
Keith Wilkinson Winchester UK
Department of Chemistry
St Mary's College
+44(0)1962-854412
http://schools.sys.uea.ac.uk/schoolnet/winchester
k.wil...@dial.pipex.com
-------------------------------------------------------------
Salane King
Thallion wrote:
sk> From: salane king <sk...@pediatrics.uams.edu>
sk> Consider why a hot air baloon rises, then you will know why.
Duh? As long as he is not weighing a gas, this will be of NO
importance.
//Thallion
DUH As if the air above the pan weighs nothing. and you are using a
kilogram scale.
William R. Penrose
In article <B.Hamilton....@irl.cri.nz> B.Ham...@irl.cri.nz (Bruce Hamilton) writes:
>I repeat. Sci.chem exists for the discussion of items of
>chemical interest, and wholesale posting by students
>who haven't performed the groundwork will inevitably
>distract from the overall signal of the group.
And that is one person's opinion. Not mine.
Bill
************************************************************
Bill Penrose, Sr. Scientist, Transducer Research, Inc.
600 North Commons Drive, Suite 117
Aurora, IL 60504
!!!Note new area code!!!
630-978-8802, fax -8854, email wpen...@interaccess.com
************************************************************
Purveyors of fine gas sensors and
contract R&D to this and nearby galaxies.
************************************************************
Bruce Hamilton
In article <01bbb31d$9dd62060$d6fa...@pn92.dial.pipex.com>
"Keith Wilkinson" <k.wil...@dial.pipex.com> writes:
>I enjoy answering questions that appear on this group, and I am encouraging
>my students to use the Internet as a resource for two reasons.
Fine, but please ensure they don't view sci.chem as a resource
to post homework questions to. Sci.chem was established as a
*discussion* group, not as a resource for students to post
questions to just so they could build their confidence.
>What I like about sci.chem is that there is always at least one question
>that a student is able to answer or comment on.
I repeat. Sci.chem exists for the discussion of items of
chemical interest, and wholesale posting by students
who haven't performed the groundwork will inevitably
distract from the overall signal of the group.
Many of the posters to sci.chem are still referred to information
sources, such as Kirk Othmer, that they should have investigated
prior to posting. If we had allowed your predecessors ( and there
have been many over the years ) to misuse sci.chem for their own
educational purposes, the group would be much different to what
it is today. That's not to say students should not post, but that
they should ensure they are contributing to the discusiion when
they post.
>Lastly, if a student uses Usenet either to pose a question and assimilate
>the replies, or else answer someone elses question, then their efforts will
>be well rewarded as their confidence increases.
Will we get a share of your salary for performing your work?
You have discovered a discussion group and you want us
to help your students develop because of the quality of the
discussion you have found here.
If you want a group that exists to help student develop, then
create it, and don't misuse sci.chem. You may believe that
I'm being unduly harsh, but the reality is sci.chem has only
retained diversity and quality because knowledgeable people
spend their valuable time adding a perception to an issue.
They stay and contribute because they also learn from others
who are skilled in another field that they are also interested in.
We all gain when discussions are informative and high quality.
Your students should only post questions to sci.chem if they
can't locate the response from the traditional chemical information
sources, and some of the common ones are described in the FAQ.
Have you and your students read the FAQ?.
Do you recall the following?
Bruce Hamilton
[ Begin sci.chem extract ]
5.1 What topics does sci.chem cover?
Sci.chem is a discussion group, and it covers the scientific discussion of
all issues concerning chemistry....
5.6 Should I post my homework question?
In general, definitely not. Your homework question is designed to challenge
you to understand an aspect of chemistry, and your teacher will have
ensured that there are appropriate resources available to you at your
institution. The library is always an excellent place to start, and the
librarians are skilled at finding information - if you ask for assistance.
However, if you find that the library and other available resources can not
fully satisfy your curiosity, then carefully outline your problem and do
post *only* to the most appropriate group. If it is the wrong group,
somebody will point you to the correct one. Do not expect to receive the
actual answer, we will carefully consider your request, and frame a response
to ensure that you need to perform some work before your can answer your own
question. The most obvious technique is to respond with a similar worked
example that is sufficiently different to ensure you can not plug in the
numbers and arrive at your correct answer. Also, remember that we are not
obliged to provide only correct answers, we can deliberately introduce
errors to ensure direct copying without comprehension results in the wrong
answer - it is not *our* homework :-). Do not expect sensible or accurate
responses if you post from anonymous servers.
[ end extract ]
Thallion
SK> From: Salane King <sk...@pediatrics.uams.edu>
SK> Consider why a hot air baloon rises, then you will know why.
Th> Duh? As long as he is not weighing a gas, this will be of NO
Th> importance.
SK> DUH As if the air above the pan weighs nothing. and you are using a
SK> kilogram scale.
Oh! If a hot object is placed on a scale, then the air above it will warm
up, and get lighter. Then the object will seem lighter, because the air
pressure just above the scale will be lower? Ahaaa! Interesting.