Science and Technology news... :: View topic

Andy Hunt · Guest

E=mc2

Energy is mass x the speed of light squared.

(According to Albert Einstein, in any case!)

Andrew

"H.J." <wenonaliar@yahoo.com> wrote in message
news:vukvh3f9mr8ka1@corp.supernews.com...
[quote]Energy - A wee little bit of mass.
Mass - A whole crapload of energy.

"T Rex" <tee.rex@lovemail.com> wrote in message
news:73269c91.0312231225.5ed9661b@posting.google.com...
Looked thru the web.

Unable to find a good site that defines or explian energy.
Mayve I did not get to see the right sites.

One site says that Energy cannot be defined or described.

How do you respond when asked to define energy - by your
kid for example ?.

[/quote]

Jerason Banes · Guest

Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FEF1DA0.4010407@citlink.net>...
[quote]Jerason Banes wrote:
cyril <meyn#ie#r.cy#ril@wan#adoo.fr//virezles#> wrote in message news:<pr9huvoc89m3agcvhamdje1lofrlb8rosb@4ax.com>...

Energy can be descibed as a "money" used to "buy" and "sell" natural
processes.

This definition is totally personnal and non-scientific :-)

A slightly more scientific definition that I like to keep in mind is
that energy is an attribute of the universe winding down...

That is an increase in entropy, not a definition of energy.
[/quote]
Actually, entropy is the natural progression of the Universe toward
its death. I>m saying that energy is an attribute of entropy. By
tapping entropy for our own purposes we can produce useful energy, or
"work". We>re contributing to the slow death of the Universe by doing
so, but in the grand scheme of things, we>re not speeding things up by
much. :-)

Thanks,
Jerason

Dan Bloomquist · Guest

Jerason Banes wrote:
[quote]Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FEF1DA0.4010407@citlink.net>...

Jerason Banes wrote:

cyril <meyn#ie#r.cy#ril@wan#adoo.fr//virezles#> wrote in message news:<pr9huvoc89m3agcvhamdje1lofrlb8rosb@4ax.com>...

Energy can be descibed as a "money" used to "buy" and "sell" natural
processes.

This definition is totally personnal and non-scientific :-)

A slightly more scientific definition that I like to keep in mind is
that energy is an attribute of the universe winding down...

That is an increase in entropy, not a definition of energy.

Actually, entropy is the natural progression of the Universe toward
its death. I>m saying that energy is an attribute of entropy. By
tapping entropy for our own purposes we can produce useful energy, or
"work". We>re contributing to the slow death of the Universe by doing
so, but in the grand scheme of things, we>re not speeding things up by
much. :-)

[/quote]
Hi Jerason,
How about a couple of assumptions to start. First, the universe is
closed. Second, the universe is expanding.

From the first assumption, the total energy in the universe is
constant. From the second, the increasing entropy is a function of
space. The only reason we can 'tap' this imbalance of 'order' is because
the expansion is not uniform. So I would wonder if entropy is a quality
of energy or the space in the universe. What happens if the universe
contracts? It would seem by the laws we know that all the energy in the
universe would return to it>s pristine state.

[quote]Thanks,
Jerason
[/quote]
Best, Dan.

--
http://lakeweb.net
http://ReserveAnalyst.com
dbAtLakewebDotCom

Harry Conover · Guest

Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FEF44EA.3040500@citlink.net>...
[quote]Harry Conover wrote:
Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FE8D8F1.2000802@citlink.net>...

T Rex wrote:

Looked thru the web.

Unable to find a good site that defines or explian energy.
Mayve I did not get to see the right sites.

One site says that Energy cannot be defined or described.

How do you respond when asked to define energy - by your
kid for example ?.

It sometimes gets confusing because there are many forms of energy.

Energy is defined. It is Force times Length in mechanics.

Sorry, Dan, but in physics that>s a definition of work. Energy by
contrast is the capacity to perform work.

Hi Harry,
Happy Holidays!

Well, maybe I have something to learn here, but let>s start with the
work-energy theorem and kinetic energy. Let>s force some mass through a
distance, what you say is not energy. Yet this mass now has an energy
equal to mv^2/2.
[/quote]
Dan, that>s not the general case. If you apply a force over a
distance, you have performed work, but that work is not usually/always
reflected in the production of either kinetic or potential energy.
Force a mass horizontally over a frictional horizontal surface for a
given distance and you may end up with no more kinetic or potential
energy than you started with...because the work you expended has ended
up as heat (which is of course another form of energy).

[quote]If you>d like, work is transfer of energy from one
system to another. Transfer of energy means that this connection you
call work must be the same stuff as energy. You are not transferring
something else. It has the same dimensions in mathematical terms, so, it
is the same.
[/quote]
Dan, I prefer to think of it this way. Work is that which is required
to be expended to accomplish configuration changes from one energy
state to another plus losses. Don>t be misled by mathematical
similarities between work and energy, since mathematics doesn>t really
care if you are dealing with apples or oranges, it>s simply an
intellectual abstration that aids in the resolution of quantitative
issues. Similarly, boolean algebra aids in the resolution of logical
issues but also is not physics.

[quote]Sorry to pick nit, but the precise definitions of fundamental units
work and energy, and the distinction between the two terms, is
critical to a clear understanding of basic mecanics.

Please show me the difference in the dimensional system. Or, if you>d
like, explain the difference.
[/quote]
Please see the above.

[quote]To illustrate, the conversion n-joules of energy to n-joules of
accomplished work is impossible, since it would require a perfect
machine to accomplish. Perfect (100% efficient) machines don>t and
cannot exist.

This is beside the point. It does not address a difference between work
and energy. It is still my contention that is is confusing to say they
are something different without clear qualification. And I can think of
nothing clear about saying 'they are different'.
[/quote]
Let me try to clarify. Work is that which must be expended to
accomplish a given physical goal, such as lifting a 1-lb weight to a
height of 10-feet. Hence, the potential energy created is 10-foot-lbs
(whatever units that tranlates to). Still, energy required to
accomplish this lift is greater than 10-foot-pounds, which is why the
distinction between energy and work is becomes so critical. It>s a
real-world issue. In the real-world, energy and work are not directely
equivalent.

The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?

Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.

Kindest regards,

Harry C.

Jeff · Guest

<snip>

[quote]The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?

[/quote]
That one>s easy - it went in heating the wires (including the internal
connections and foil in a real case) during the voltage mismatch. It>s the
same reason a switched capacitor power supply will inherently always have
efficiency problems.

[quote]Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.

Kindest regards,

Harry C.[/quote]

Jo Stein · Guest

On Sun, 28 Dec 2003 22:50:28 -0000, "Andy Hunt"
<mailbox@megalomania.co.uk> wrote in
<EnJHb.2291$Mv.922@newsfep3-gui.server.ntli.net>:

[quote]E=mc2

Energy is mass x the speed of light squared.

(According to Albert Einstein, in any case!)

Energy is best described by P. W. Atkins:[/quote]
--
"We are the children of chaos, and the deep structure of change is
decay. At the root, there is only corruption, and the unstemmable
tide of chaos. Gone is purpose; all that is left is direction.
This is the bleakness we have to accept as we peer deeply and
dispassionately into the heart of the Universe."
The 2nd law, p. 200, by P. W. Atkins

Don Lancaster · Guest

Jeff wrote:
[quote]
snip

The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?

That one>s easy - it went in heating the wires (including the internal
connections and foil in a real case) during the voltage mismatch. It>s the
same reason a switched capacitor power supply will inherently always have
efficiency problems.

Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.

Kindest regards,

Harry C.
[/quote]
The energy lost to charging through a resistor is independent of the
resistor value and equals one half the total.

Should the resistance be nonzero, heat is produced.
Should the resistance be zero, the spark radiates electromagnetically.
Or the model fails and you have to consider resonant inductance, which
also radiates electromagnetically.

--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com fax 847-574-1462

Please visit my GURU>s LAIR web site at http://www.tinaja.com

Dan Bloomquist · Guest

Harry Conover wrote:
[quote]Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FEF44EA.3040500@citlink.net>...
Harry Conover wrote:
Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FE8D8F1.2000802@citlink.net>...
T Rex wrote:
Looked thru the web.

Unable to find a good site that defines or explian energy.
Mayve I did not get to see the right sites.

One site says that Energy cannot be defined or described.

How do you respond when asked to define energy - by your
kid for example ?.

It sometimes gets confusing because there are many forms of energy.

Energy is defined. It is Force times Length in mechanics.

Sorry, Dan, but in physics that>s a definition of work. Energy by
contrast is the capacity to perform work.

Well, maybe I have something to learn here, but let>s start with the
work-energy theorem and kinetic energy. Let>s force some mass through a
distance, what you say is not energy. Yet this mass now has an energy
equal to mv^2/2.

Dan, that>s not the general case. If you apply a force over a
distance, you have performed work, but that work is not usually/always
reflected in the production of either kinetic or potential energy.
Force a mass horizontally over a frictional horizontal surface for a
given distance and you may end up with no more kinetic or potential
energy than you started with...because the work you expended has ended
up as heat (which is of course another form of energy).
[/quote]
Hi Harry,
The topic is the work-energy theorem. It is completely unnecessary to
drag the baggage of friction into this.

See Physics for Scientist and Engineers chapter 7
Lectures on Physics vol I chapters 13 and 14.

[quote]If you>d like, work is transfer of energy from one
system to another. Transfer of energy means that this connection you
call work must be the same stuff as energy. You are not transferring
something else. It has the same dimensions in mathematical terms, so, it
is the same.

Dan, I prefer to think of it this way. Work is that which is required
to be expended to accomplish configuration changes from one energy
state to another plus losses.
[/quote]
Configuration state? I don>t know what you mean. But I did write, 'work
is transfer of energy from one system to another'. We don>t need to drag
friction into this.

[quote]Don>t be misled by mathematical
similarities between work and energy, since mathematics doesn>t really
care if you are dealing with apples or oranges, it>s simply an
intellectual abstration that aids in the resolution of quantitative
issues.
[/quote]
When using the dimensional system it is apples and apples. One of the
only abstraction would be to hide ML/T^2 in F.

[quote]Similarly, boolean algebra aids in the resolution of logical
issues but also is not physics.
[/quote]
If speaking of physical quantities, it is physics.

[quote]Sorry to pick nit, but the precise definitions of fundamental units
work and energy, and the distinction between the two terms, is
critical to a clear understanding of basic mecanics.

Please show me the difference in the dimensional system. Or, if you>d
like, explain the difference.

Please see the above.
[/quote]
Sorry Harry, but muddle. My books say FL is a measure of energy.

[quote]To illustrate, the conversion n-joules of energy to n-joules of
accomplished work is impossible, since it would require a perfect
machine to accomplish. Perfect (100% efficient) machines don>t and
cannot exist.

This is beside the point. It does not address a difference between work
and energy. It is still my contention that is is confusing to say they
are something different without clear qualification. And I can think of
nothing clear about saying 'they are different'.

Let me try to clarify. Work is that which must be expended to
accomplish a given physical goal, such as lifting a 1-lb weight to a
height of 10-feet. Hence, the potential energy created is 10-foot-lbs
(whatever units that tranlates to). Still, energy required to
accomplish this lift is greater than 10-foot-pounds, which is why the
distinction between energy and work is becomes so critical. It>s a
real-world issue. In the real-world, energy and work are not directely
equivalent.
[/quote]
See the references I cited. They say work and energy are the same.

[quote]The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?
[/quote]
You can not evade the voltage drop while transferring the charge so the
energy went into heat. Use a switching power supply and you could get
most of the charge to transfer.

[quote]Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.
[/quote]
Loss does not have to enter into this. See the work-energy theorem. It
can be discussed just fine without considering friction.

[quote]
Kindest regards,

Harry C.
[/quote]
Best, Dan.

--
http://lakeweb.net
http://ReserveAnalyst.com
dbAtLakewebDotCom

Jerason Banes · Guest

Hi Dan,

[quote]Hi Jerason,
How about a couple of assumptions to start. First, the universe is
closed. Second, the universe is expanding.
[/quote]
In fact, that>s basic high school physics. As they teach, "There is a
finite amount of energy and matter in the Universe. No matter or
energy may be created or destroyed, but they may be converted." This
seems like a reasonable assumption to make for this discussion. :-)

[quote]From the first assumption, the total energy in the universe is
constant. From the second, the increasing entropy is a function of
space. The only reason we can 'tap' this imbalance of 'order' is because
the expansion is not uniform. So I would wonder if entropy is a quality
of energy or the space in the universe. What happens if the universe
contracts? It would seem by the laws we know that all the energy in the
universe would return to it>s pristine state.
[/quote]
The current evidence in physics, is that the Universe will not
contract and continue to expand forever. In fact, if super-string
theory is shown to be correct, the likelihood of contraction is zero.
According to super-string theory (part of M-Theory), the matter and
energy we>re using is the result of a "splat" between universes. The
force of that splat will eventually dissipate or be replaced when the
Universes go "splat" again.

BTW, most textbooks talk about matter to energy and energy to matter
conversion, but leave out the space-time curvature to matter/energy
conversion. The Universe can be "warped" such that matter and energy
are produced, or converted back into space-time. The "splat" theory
would cause a forceful expansion, thus producing the matter and
energy.

No, I am not a physicist. It>s just my hobby. I>m sure I got one or
two points slightly incorrect.

Thanks,
Jerason

Harry Conover · Guest

Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FF054F1.1040807@citlink.net>...
[quote]Harry Conover wrote:
Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FEF44EA.3040500@citlink.net>...
Harry Conover wrote:
Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FE8D8F1.2000802@citlink.net>...
T Rex wrote:
Looked thru the web.

Unable to find a good site that defines or explian energy.
Mayve I did not get to see the right sites.

One site says that Energy cannot be defined or described.

How do you respond when asked to define energy - by your
kid for example ?.

It sometimes gets confusing because there are many forms of energy.

Energy is defined. It is Force times Length in mechanics.

Sorry, Dan, but in physics that>s a definition of work. Energy by
contrast is the capacity to perform work.

Well, maybe I have something to learn here, but let>s start with the
work-energy theorem and kinetic energy. Let>s force some mass through a
distance, what you say is not energy. Yet this mass now has an energy
equal to mv^2/2.

Dan, that>s not the general case. If you apply a force over a
distance, you have performed work, but that work is not usually/always
reflected in the production of either kinetic or potential energy.
Force a mass horizontally over a frictional horizontal surface for a
given distance and you may end up with no more kinetic or potential
energy than you started with...because the work you expended has ended
up as heat (which is of course another form of energy).

Hi Harry,
The topic is the work-energy theorem. It is completely unnecessary to
drag the baggage of friction into this.
[/quote]
Dan, if you pick up a physics 101 text, you>ll find that
friction/losses directly relate to any discussion of work vs. energy.
In Sears and Zemansky>s "University Physics", it is stated that "The
work done by the outside agent is equal to the change in kinetic
energy plus the change in gravitational energy plus the work done
against friction."

In other words: Work = Delta-Energy - Losses

The losses may be frictional, resistive, radiative, or otherwise. The
point to be made is that Work does not equal (change in) energy,
except in a hypothetical, idealized world. While the dimensions of
Work and Energy are identical, their quantities themselves (in the
real-world) always differ.

This is basic physics, and the reason why different terms exist to
distinguish between these two parameters.

[quote]See Physics for Scientist and Engineers chapter 7
Lectures on Physics vol I chapters 13 and 14.
[/quote]
Sorry, but I>m not familiar with these works. I suspect that if you
examine their discussions carefully, you>ll find that they are making
simplifying assumptions that eliminate losses.

[quote]If you>d like, work is transfer of energy from one
system to another. Transfer of energy means that this connection you
call work must be the same stuff as energy. You are not transferring
something else. It has the same dimensions in mathematical terms, so, it
is the same.

Dan, I prefer to think of it this way. Work is that which is required
to be expended to accomplish configuration changes from one energy
state to another plus losses.

Configuration state? I don>t know what you mean. But I did write, 'work
is transfer of energy from one system to another'. We don>t need to drag
friction into this.
[/quote]
See the above. By change in configuration state, I simply mean the
physical configuration that existed before an event compared with that
which existed afterwards.

[quote]Don>t be misled by mathematical
similarities between work and energy, since mathematics doesn>t really
care if you are dealing with apples or oranges, it>s simply an
intellectual abstration that aids in the resolution of quantitative
issues.

When using the dimensional system it is apples and apples. One of the
only abstraction would be to hide ML/T^2 in F.
[/quote]
You>ve completely lost me here.

[quote]Similarly, boolean algebra aids in the resolution of logical
issues but also is not physics.

If speaking of physical quantities, it is physics.
[/quote]
That>s certain a matter of opinion. As a physicist, I regard
mathematic as simply another tool that aids in the evaluation of
physical relationships, which of course alrady exist in nature without
the aid of mathematics.

[quote]Sorry to pick nit, but the precise definitions of fundamental units
work and energy, and the distinction between the two terms, is
critical to a clear understanding of basic mecanics.

Please show me the difference in the dimensional system. Or, if you>d
like, explain the difference.

Please see the above.

Sorry Harry, but muddle. My books say FL is a measure of energy.
[/quote]
Dan, what the heck is FL? If it suggest that force x disance = energy,
you>d be well advised to consult a more advanced book! :-)
[quote]
To illustrate, the conversion n-joules of energy to n-joules of
accomplished work is impossible, since it would require a perfect
machine to accomplish. Perfect (100% efficient) machines don>t and
cannot exist.

This is beside the point. It does not address a difference between work
and energy. It is still my contention that is is confusing to say they
are something different without clear qualification. And I can think of
nothing clear about saying 'they are different'.

Let me try to clarify. Work is that which must be expended to
accomplish a given physical goal, such as lifting a 1-lb weight to a
height of 10-feet. Hence, the potential energy created is 10-foot-lbs
(whatever units that tranlates to). Still, energy required to
accomplish this lift is greater than 10-foot-pounds, which is why the
distinction between energy and work is becomes so critical. It>s a
real-world issue. In the real-world, energy and work are not directely
equivalent.

See the references I cited. They say work and energy are the same.
[/quote]
In that case, they must be written at the highschool level, because it
is a physical fact that work and energy are definitely not the same.
[quote]
The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?

You can not evade the voltage drop while transferring the charge so the
energy went into heat. Use a switching power supply and you could get
most of the charge to transfer.
[/quote]
Transfer of charge is not the issue, since charge is always conserved.
Also, a switching power supply will not alter the loss figure.

[quote]Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.

Loss does not have to enter into this. See the work-energy theorem. It
can be discussed just fine without considering friction.
[/quote]
Sorry, no. To consider Work = Energy (change) implicitly requires a
simplifying assumption requiring that one forget about real-world
losses. It>s a conceptual simplification done only to allow beginning
students at the highschools and college entry level to grasp basic
ideas.

In a way it>s fully equivalent to providing problems to starting EE
students that alway involve perfect, loss-free, lumped parameter
components.

Kindest regards, and best wishes for a Happy New Year!

Harry C.

Roland Paterson-Jones · Guest

Mike, you>re one of the good guys, so...

Check back on the alt.en.hy newsgroups for many discussions on exergy.

In short. Energy is a book-keeping value that is exchanged between systems
without loss. Entropy is a measure of the disorganisation of a system.
Exergy is a precise measure of the ability to do (useful) work in some
environment.

Exergy is a 'useful' expression of the energy in a system, because (and only
because) it considers the environment.

The 'exergy' of a sample in some environment is the ability of that sample
(ice cube, petrol tank, battery) to do 'work', i.e. mechanical energy (force
times distance) in that environment.

As the Don has stated many times an ice cube in the tropics has (positive)
exergy, even tho it>s internal energy is lower than a similar glass of
water.

Best wishes for the new year
Roland

"Mike Ackerman" <mackermNOSPAM@mailpuppy.com> wrote in message
news:3FECC23E.F1CA715F@mailpuppy.com...
[quote]

Roland Paterson-Jones wrote:

Nope, energy is the capacity or capability to do work in outer space,
where
the temperature is absolute zero.

'Exergy', on the other hand, is the capacity or capability to do work in
any
particular normal situation.

WOW! At last an understandable definition for "exergy".

Mike Ackerman[/quote]

Roland Paterson-Jones · Guest

"Jerason Banes" <jbanes@techie.com> wrote in message

[quote]A slightly more scientific definition that I like to keep in mind is
that energy is an attribute of the universe winding down. The same is
actually true for matter as well, but to keep it simple, we can think
of the universe as a bunch of rocks rolling down a hill. If you push a
rock ahead of you, it speeds up and you slow down. By doing this, you
effectively "unbalance" the current course of the rocks and create
what we think of as work.
[/quote]
Mmm, this appeals to me after a few tokes. Are you claiming that 'energy'
is, in effect a 'derivative' in the calculus sense (i.e. 'differential'), of
the expansion of the universe?

[quote]Thus energy is the universe winding down.
[/quote]
So, according to your hypothesis, as the universe winds down, there will be
increasingly less energy available (since the rate of expansion of the
universe is on the decrease)?

Mmm, but entropy has been typically associated with cycles of universal (in
the sense of 'the universe') expansion and contraction.

[quote]Work is attempts to unbalance that energy in order to make something
useful happen.
[/quote]
No, work is simply local exergy exchange.

Roland

Dan Bloomquist · Guest

Harry Conover wrote:
[quote]Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FF054F1.1040807@citlink.net>...

Harry Conover wrote:

Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FEF44EA.3040500@citlink.net>...

Harry Conover wrote:

Dan Bloomquist <lakeweb@citlink.net> wrote in message news:<3FE8D8F1.2000802@citlink.net>...

T Rex wrote:

Looked thru the web.

Unable to find a good site that defines or explian energy.
Mayve I did not get to see the right sites.

One site says that Energy cannot be defined or described.

How do you respond when asked to define energy - by your
kid for example ?.

It sometimes gets confusing because there are many forms of energy.

Energy is defined. It is Force times Length in mechanics.

Sorry, Dan, but in physics that>s a definition of work. Energy by
contrast is the capacity to perform work.

Well, maybe I have something to learn here, but let>s start with the
work-energy theorem and kinetic energy. Let>s force some mass through a
distance, what you say is not energy. Yet this mass now has an energy
equal to mv^2/2.

Dan, that>s not the general case. If you apply a force over a
distance, you have performed work, but that work is not usually/always
reflected in the production of either kinetic or potential energy.
Force a mass horizontally over a frictional horizontal surface for a
given distance and you may end up with no more kinetic or potential
energy than you started with...because the work you expended has ended
up as heat (which is of course another form of energy).

Hi Harry,
The topic is the work-energy theorem. It is completely unnecessary to
drag the baggage of friction into this.

Dan, if you pick up a physics 101 text, you>ll find that
friction/losses directly relate to any discussion of work vs. energy.
[/quote]
I>ve cited my references.

[quote]In Sears and Zemansky>s "University Physics", it is stated that "The
work done by the outside agent is equal to the change in kinetic
energy plus the change in gravitational energy plus the work done
against friction."
[/quote]
Page and chapter. I>d like to see the context next time I get to ASU.

[quote]In other words: Work = Delta-Energy - Losses

The losses may be frictional, resistive, radiative, or otherwise. The
point to be made is that Work does not equal (change in) energy,
except in a hypothetical, idealized world. While the dimensions of
Work and Energy are identical, their quantities themselves (in the
real-world) always differ.

This is basic physics, and the reason why different terms exist to
distinguish between these two parameters.

See Physics for Scientist and Engineers chapter 7
Lectures on Physics vol I chapters 13 and 14.

Sorry, but I>m not familiar with these works. I suspect that if you
examine their discussions carefully, you>ll find that they are making
simplifying assumptions that eliminate losses.

If you>d like, work is transfer of energy from one
system to another. Transfer of energy means that this connection you
call work must be the same stuff as energy. You are not transferring
something else. It has the same dimensions in mathematical terms, so, it
is the same.

Dan, I prefer to think of it this way. Work is that which is required
to be expended to accomplish configuration changes from one energy
state to another plus losses.

Configuration state? I don>t know what you mean. But I did write, 'work
is transfer of energy from one system to another'. We don>t need to drag
friction into this.

See the above. By change in configuration state, I simply mean the
physical configuration that existed before an event compared with that
which existed afterwards.

Don>t be misled by mathematical
similarities between work and energy, since mathematics doesn>t really
care if you are dealing with apples or oranges, it>s simply an
intellectual abstration that aids in the resolution of quantitative
issues.

When using the dimensional system it is apples and apples. One of the
only abstraction would be to hide ML/T^2 in F.

You>ve completely lost me here.
[/quote]
To abstract is to hide complexities that you don>t need to see.

[quote]Similarly, boolean algebra aids in the resolution of logical
issues but also is not physics.

If speaking of physical quantities, it is physics.

That>s certain a matter of opinion. As a physicist, I regard
mathematic as simply another tool that aids in the evaluation of
physical relationships, which of course alrady exist in nature without
the aid of mathematics.
[/quote]
The beauty of physics is that math and observations fit like a jig saw.

[quote]Sorry to pick nit, but the precise definitions of fundamental units
work and energy, and the distinction between the two terms, is
critical to a clear understanding of basic mecanics.

Please show me the difference in the dimensional system. Or, if you>d
like, explain the difference.

Please see the above.

Sorry Harry, but muddle. My books say FL is a measure of energy.

Dan, what the heck is FL? If it suggest that force x disance = energy,
you>d be well advised to consult a more advanced book! :-)
[/quote]
I>ll check yours out. The ones I cited aren>t grade school stuff.

[quote]To illustrate, the conversion n-joules of energy to n-joules of
accomplished work is impossible, since it would require a perfect
machine to accomplish. Perfect (100% efficient) machines don>t and
cannot exist.

This is beside the point. It does not address a difference between work
and energy. It is still my contention that is is confusing to say they
are something different without clear qualification. And I can think of
nothing clear about saying 'they are different'.

Let me try to clarify. Work is that which must be expended to
accomplish a given physical goal, such as lifting a 1-lb weight to a
height of 10-feet. Hence, the potential energy created is 10-foot-lbs
(whatever units that tranlates to). Still, energy required to
accomplish this lift is greater than 10-foot-pounds, which is why the
distinction between energy and work is becomes so critical. It>s a
real-world issue. In the real-world, energy and work are not directely
equivalent.

See the references I cited. They say work and energy are the same.

In that case, they must be written at the highschool level, because it
is a physical fact that work and energy are definitely not the same.
[/quote]
If you insist, but I>m not buying it. So far every definition I>ve seen
puts them in the same bag. (You might like 'Lectures on Physics'.)

[quote]The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?

You can not evade the voltage drop while transferring the charge so the
energy went into heat. Use a switching power supply and you could get
most of the charge to transfer.

Transfer of charge is not the issue, since charge is always conserved.
[/quote]
Yes, yes! Very sloppy of me. I meant transfer of energy.

[quote]Also, a switching power supply will not alter the loss figure.
[/quote]
Certainly it will! (Want the details?)

[quote]Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.

Loss does not have to enter into this. See the work-energy theorem. It
can be discussed just fine without considering friction.

Sorry, no. To consider Work = Energy (change) implicitly requires a
simplifying assumption requiring that one forget about real-world
losses.
[/quote]
I disagree.

[quote]It>s a conceptual simplification done only to allow beginning
students at the highschools and college entry level to grasp basic
ideas.
[/quote]
And friction seems to be left as another subject from what I read. I
also checked my 'Handbook of Engineering Fundamentals', Eshbach.

[quote]
In a way it>s fully equivalent to providing problems to starting EE
students that alway involve perfect, loss-free, lumped parameter
components.

Kindest regards, and best wishes for a Happy New Year!

Harry C.
[/quote]
And I wish you a delightful New Year!
Best, Dan.

--
http://lakeweb.net
http://ReserveAnalyst.com
dbAtLakewebDotCom

Dan Bloomquist · Guest

Jerason Banes wrote:
[quote]Hi Dan,

Hi Jerason,
How about a couple of assumptions to start. First, the universe is
closed. Second, the universe is expanding.

In fact, that>s basic high school physics. As they teach, "There is a
finite amount of energy and matter in the Universe. No matter or
energy may be created or destroyed, but they may be converted." This
seems like a reasonable assumption to make for this discussion. :-)
[/quote]
Yes, but it is not only finite, it is an invariant.

[quote]From the first assumption, the total energy in the universe is
constant. From the second, the increasing entropy is a function of
space. The only reason we can 'tap' this imbalance of 'order' is because
the expansion is not uniform. So I would wonder if entropy is a quality
of energy or the space in the universe. What happens if the universe
contracts? It would seem by the laws we know that all the energy in the
universe would return to it>s pristine state.

The current evidence in physics, is that the Universe will not
contract and continue to expand forever.
[/quote]
I>m curious about this evidence.

[quote]In fact, if super-string
theory is shown to be correct, the likelihood of contraction is zero.
According to super-string theory (part of M-Theory), the matter and
energy we>re using is the result of a "splat" between universes. The
force of that splat will eventually dissipate or be replaced when the
Universes go "splat" again.
[/quote]
I am ignorant of super string. But one catch is whether we will ever
make a super-string observation. So, for now, it is philosophical.

[quote]BTW, most textbooks talk about matter to energy and energy to matter
conversion, but leave out the space-time curvature to matter/energy
conversion. The Universe can be "warped" such that matter and energy
are produced, or converted back into space-time. The "splat" theory
would cause a forceful expansion, thus producing the matter and
energy.
[/quote]
I purposefully left 'time' out when I posted. I have no idea how to four
vector entropy. Just as I left the E=mc^2 stuff alone because space-time
requires tossing a lot of preconceived notions about space-time.

See above on string-theory. If we use the existing laws, there is no
producing matter and energy. The primordial hyper expansion is a theory
to get use beyond the unknown we would have to deal with, without it.

[quote]
No, I am not a physicist. It>s just my hobby. I>m sure I got one or
two points slightly incorrect.
[/quote]
And I>ll put my foot in my mouth on a regular basis, as I>m just a
novice. :) But what the hell, this is as good a place as any to learn.

[quote]
Thanks,
Jerason
[/quote]
Best, Dan.

--
http://lakeweb.net
http://ReserveAnalyst.com
dbAtLakewebDotCom

Jeff · Guest

"Don Lancaster" <don@tinaja.com> wrote in message
news:3FF0477C.171E7EE9@tinaja.com...
[quote]Jeff wrote:

snip

The classic example of this is an old freshman physics problem. IIRC,
when you discharge a capacitor charged to 100 volts into an identical
uncharged capacitor, the result is both capacitors now are charged to
50 volts each, but mysteriously energy has vanished. Where did it go?

That one>s easy - it went in heating the wires (including the internal
connections and foil in a real case) during the voltage mismatch. It>s
the
same reason a switched capacitor power supply will inherently always
have
efficiency problems.

Dan, the essence of this pontification is that you cannot simply
interchange energy with work. Agreed that both units are of the same
dimensions, but it is physically impossible to exchange one for the
other without loss.

Kindest regards,

Harry C.

The energy lost to charging through a resistor is independent of the
resistor value and equals one half the total.
[/quote]

Yes, lets go one step further and show it:

E = CV^2, at 1/2 V, times two gives E = 2*C(V/2)^2 = 2*C(V^2/4) = CV^2 / 2,
therefore half the energy is gone, so the only place for it to go is in the
resistance (or other radiated forms listed below), otherwise it would be a
violation of the first law of thermodynamics.

[quote]
Should the resistance be nonzero, heat is produced.
Should the resistance be zero, the spark radiates electromagnetically.
[/quote]
Zero resistance is not likely, but can be approximated. Also, the plasma
created in the air spark has resistance. Another thing not to forget about
is the energy released in vaporizing the metal as the arc erodes it! A nice
100,000 uf computer cap I have will make a 2 to 3 foot diameter shower of
sparks when charged up to about 14 V and shorted with a screw driver
(admittedly, some of the sparks are from the iron igniting).

[quote]Or the model fails and you have to consider resonant inductance, which
also radiates electromagnetically.
[/quote]
You must be talking about dinky little capacitors with long leads charged up
to very high voltages for that to add up to much!

[quote]
--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com fax 847-574-1462

Please visit my GURU>s LAIR web site at http://www.tinaja.com[/quote]


www.GetXFactor.com Leading Technology, Science, Agriculture News and information	Part of the Identityscape.com network... getxfactor.com jmoodmusic.com smartbusinesschoices.com mintdepot.com lowfaresalways.com evangelicalview.com shoppingpodder.com soproudlywehail.com webnews.ws currenthumor.com

Science and Technology news... Forum Index -> Energy - Hydrogen Forum	Goto page Previous 1, 2, 3, 4 Next
Page 3 of 4