Energy...What is it?
Xtrchessreal
I don't want to see E=mc^2 because that just defines a process.
We see the rocks and grass. We know what light is. Electric fields,
Magnetic fields, are apparent by their presence and measured by Flux
and Density etc.
What is energy? Yeah we know that when electrons loose an orbital they
emit energy...what is that?
At least matter has some kind of mass and velocity or acceleration. Is
it heat? What is heat?
X
Publius
news:1169887915.0...@j27g2000cwj.googlegroups.com:
> Anyone here know what energy is?
> What is energy? Yeah we know that when electrons loose an orbital they
> emit energy...what is that?
Energy is the capacity to do work --- to change the value of at least one
variable describing the state of a system.
AE
> Anyone here know what energy is?
It's a property that stays constant in a closed system, like linear and
angular momentum, electric and color charge.
> I don't want to see E=mc^2 because that just defines a process.
>
> We see the rocks and grass. We know what light is. Electric fields,
> Magnetic fields, are apparent by their presence and measured by Flux
> and Density etc.
>
> What is energy? Yeah we know that when electrons loose an orbital
> they emit energy...what is that?
When electrons are changing from one orbital potential energy changes
and the difference gets transformed into electromagnetic energy / a
photon.
> At least matter has some kind of mass and velocity or acceleration.
> Is it heat?
Not necessarily. Heat is a special form of energy.
> What is heat?
Energy in transit.
> X
--
Sir Frederick
Matter/energy, just as space/time are manifests. They are
effectively by magic. No one knows what or why they are.
Frustrating situation, but there it is, no choice.
Recently it is being surmised that other aspects of the
situation are also manifest by this existential magic.
Suggestions include such as : "organizing principles",
qualia, personification, etc.
Sammybaby
On 27 Jan, 10:00, Publius <m.publ...@nospam.comcast.net> wrote:
> "Xtrchessreal" <XtrChessr...@gmail.com> wrote innews:1169887915.0...@j27g2000cwj.googlegroups.com:
>
> > Anyone here know what energy is?
> > What is energy? Yeah we know that when electrons loose an orbital they
> > emit energy...what is that?Energy is the capacity to do work --- to change the value of at least one
> variable describing the state of a system.
but in an einsteinian universe where time is the fourth dimension,
ideas such as capacity - where the future is somehow here in the
present - seem anachronisms. Don't we simply have adjacent states?
Is 'could cause' a valid concept in an einsteinian universe?
I understand it as a practical one from our limited day to day life.
andy-k
> Anyone here know what energy is?
An isolated physical system may undergo changes in its qualitative and
quantitative aspects, and certain aspects are given special consideration
because they remain invariant. The name 'energy' is given to just such an
aspect that may undergo qualitative changes but that remains quantitatively
invariant -- i.e. we describe physical systems in terms of the invariants
we may abstract with regard to those systems, and energy is nothing more
than a name we give to one of those abstracted invariants.
tg
What is mass?
What is an electric field?
What is a magnetic field?
What is velocity?
Do any of these things have meaning independent of measurement? Why is
energy different?
-tg
AE
Theories of relativity don't violate causality.
--
AE
Mass and velocity are aspects we are able to experience in our daily
life.
We can even see the effects of electric and magnetic fields.
The problem with energy is, that we are able to observe special forms
of energy being transmitted (e.g. electromagnetic waves, heat), but
energy as such can't be perceived.
jusholm
"Xtrchessreal" <XtrChe...@gmail.com> wrote in message
news:1169887915.0...@j27g2000cwj.googlegroups.com...
Energy is just another word for anything we can detect therefore its
defining feature is that it can effect our detectors.
jusholm
jusholm
Substance from a Naturalistic and scientific viewpoint is 'point-field' and
as such may not be further analysable. Point-field is to say that a
particular spatial-temporal location certain effect will be observed, this
may even apply at the level of Strings if they prove to be true. The natural
world is an energetic world, energy is the power to effect. Matter is energy
and energy is energy, its all energy. So a point-field is a spatial-temporal
area where certain energetic effects can predictably be observed. The
objects, and properties, of our experience are complex conglomeration and
interactions of these tiny point-fields. It is wrong, strictly, to say that
an object is 10cm across, in truth it is so-and-so many point-fields across,
billions. The reason it has any width at all is that the point-fields exist
and exclude each other. Also they have certain attractions to each other
which tend to keep them together. In this way larger objects are made of
them. Equally it is not true that an object gives off light at a frequency
of 525nm, strictly. In fact, mostly, each individual point-field of an
object tends to redirect, or emit, photons/waves, of that frequency. At the
eye, presumably, only certain proportion of these photons at slightly
varying energy levels are detected, so only an averaged sample of the light
is sensed. In a sense we do not 'see' any of the point-fields, the real
objects, themselves but a net of their effects.
Immortalist
On Jan 27, 12:51 am, "Xtrchessreal" <XtrChessr...@gmail.com> wrote:
> Anyone here know what energy is?
>
a still pool of wate
no wave indeed
the hand stireth
hence energy changeth
The word energy is widely used in various spheres of life, however,
the meanings ascribed to the word are not always precisely identical,
perhaps because there is no universal definition of the word. Thus,
although the word has its roots in the ancient science, today it is
used widely.
Perhaps, a really universal definition of the term energy could be:
a potential for
causing a
change
This definition encompasses nearly all the present usages of the term,
because energy is most often viewed as the cause for changes that
humanity observes.
http://en.wikipedia.org/wiki/Energy
http://en.wikipedia.org/wiki/Energy_%28disambiguation%29
http://en.wikipedia.org/wiki/List_of_energy_topics
Energy is a quantifiable state function of every physical system.
Energy allows one to predict how much work a physical system could be
made to do, or how much heat it can exchange. In general, energy is
inferred whenever there is a change in the properties of an object or
system. This is where the early exploration of the nature of energy
began. As our understanding of the nature of energy progressed,
scientists found it to exist in many forms not readily observable by
the average unaided observer. In fact, in some cases the presence of
particular types of energy prevents changes from being easily observed
in a particular object or system. Empirical observations have shown
that the total quantity of energy is conserved.
http://en.wikipedia.org/wiki/Category:Energy
In the physical sciences, a state of matter is one of the many ways
that matter can interact with itself to form a macroscopic, homogenous
phase. The most familiar examples of states of matter are solids,
liquids, and gases.
States of matter are sometimes confused with phases. This is likely
due to the fact that in many example systems, the familiar phase
transitions are also transformations of the state of matter. In the
example of water, the phases of ice, liquid water, and water vapor are
commonly recognized. The common phase transitions observed in a one
component system containing only water are melting/solidification
(liquid/solid), evaporation/condensation (liquid/gas) and sublimation/
deposition (solid/gas)
http://en.wikipedia.org/wiki/States_of_matter
In general, two different states of a system are in different phases
if there is an abrupt change in their physical properties while
transforming from one state to the other. Conversely, two states are
in the same phase if they can be transformed into one another without
any abrupt changes. There are, however, exceptions to this statement
-- for example the liquid-gas critical point discussed below in the
Phase Diagrams section.
An important point is that different types of phases are associated
with different physical qualities. When discussing the solid, liquid,
and gaseous phases, we talked about rigidity and compressibility, and
the effects of varying the pressure and volume, because those are the
relevant properties that distinguish a solid, a liquid, and a gas.
http://en.wikipedia.org/wiki/Phase_%28matter%29
A cooling curve is a line graph that represents the change of phase of
matter, typically from either a gas to a solid or a liquid to a solid.
Time is used in the x-axis while temperature is used for the y-axis.
They are often used in chemistry and physics, and can apply
(misleadingly) to matter behaviour during heating, as well as during
cooling.
...different phases of matter are associated with different
(energy_levels). Steam at 100°C is the same temperature, but contains
much more thermal energy than liquid water at 100°C. The same goes for
water and ice at 0°C. This is because molecules of water are much more
free to move around as a gas than as a liquid, and that freedom of
movement means there is much more kinetic energy associated with each
molecule, and that energy is transferred as the substance shifts phase
- explaining why energy seemingly disappears when boiling a kettle.
http://en.wikipedia.org/wiki/Cooling_curve
In physics, dissipation embodies the concept of a dynamical system
where important mechanical modes, such as waves or oscillations, lose
energy over time, typically due to the action of friction or
turbulence. The lost energy is converted into heat, raising the
temperature of the system. Such systems are called dissipative
systems.
Dissipating forces are those which which can not be described by
Hamiltonian formalism. Losely speaking, friction and all similar
forces which result in decoherency of energy, that is, conversion of
coherent or directed energy flow into an indirected or more isotropic
distribution of energy.
http://en.wikipedia.org/wiki/Dissipation
[spoiler]
The early universe was filled homogeneously and isotropically with an
incredibly high energy density and concomitantly huge temperatures and
pressures. It expanded and cooled, going through phase transitions
pertinent to elementary particles.
Approximately 10-35 seconds after the Planck epoch a phase transition
caused the universe to experience exponential growth during a period
called cosmic inflation. After inflation stopped, the material
components of the universe were in the form of a quark-gluon plasma
(also including all other particles-and perhaps experimentally
produced recently as a quark-gluon liquid [3]) in which the
constituent particles were all moving relativistically. As the
universe continued growing in size, the temperature dropped. At a
certain temperature, by an as-yet-unknown transition called
baryogenesis, the quarks and gluons combined into baryons such as
protons and neutrons, somehow producing the observed asymmetry between
matter and antimatter. Still lower temperatures led to further
symmetry breaking phase transitions that put the forces of physics and
elementary particles into their present form. Later, some protons and
neutrons combined to form the universe's deuterium and helium nuclei
in a process called Big Bang nucleosynthesis. As the universe cooled,
matter gradually stopped moving relativistically and its rest mass
energy density came to gravitationally dominate that of radiation.
After about 300,000 years the electrons and nuclei combined into atoms
(mostly hydrogen); hence the radiation decoupled from matter and
continued through space largely unimpeded. This relic radiation is the
cosmic microwave background.
Over time, the slightly denser regions of the nearly uniformly
distributed matter gravitationally attracted nearby matter and thus
grew even denser, forming gas clouds, stars, galaxies, and the other
astronomical structures observable today. The details of this process
depend on the amount and type of matter in the universe. The three
possible types are known as cold dark matter, hot dark matter, and
baryonic matter. The best measurements available (from WMAP) show that
the dominant form of matter in the universe is cold dark matter. The
other two types of matter make up less than 20% of the matter in the
universe.
The universe today appears to be dominated by a mysterious form of
energy known as dark energy. Approximately 70% of the total energy
density of today's universe is in this form. This dark energy causes
the expansion of the universe to deviate from a linear velocity-
distance relationship, observed as a faster than expected expansion at
very large distances. Dark energy in its simplest formulation takes
the form of a cosmological constant term in Einstein's field equations
of general relativity, but its composition is unknown and, more
generally, the details of its equation of state and relationship with
the standard model of particle physics continue to be investigated
both observationally and theoretically.
All these observations are encapsulated in the ?CDM model of
cosmology, which is a mathematical model of the Big Bang with six free
parameters. Mysteries appear as one looks closer to the beginning,
when particle energies were higher than can yet be studied by
experiment. There is no compelling physical model for the first 10-33
seconds of the universe, before the phase transition that grand
unification theory predicts. At the "first instant", Einstein's theory
of gravitation predicts a gravitational singularity where densities
become infinite.[15] To resolve this paradox, a theory of quantum
gravitation is needed. Understanding this period of the history of the
universe is one of the greatest unsolved problems in physics.
http://en.wikipedia.org/wiki/Big_bang
[one hot "feild" cooled and particles/forces "FROOZE_OUT!" into the
non-coherent -distribution- thus setting up potential unequal areas
interacting and trading the balance and walla e-n-e-r-g-y eeeee,
maaiiim]
Fundamental Interactions (The Four Forces)
The four different types of interaction that can occur between bodies.
These interactions can take place even when the bodies are not in
physical contact and together they account for all the observed forces
that occur in the universe. While the unification of these four types
of interaction into one model, theory, or set of equations has long
been the aim of physicists, this has not yet been achieved, although
progress has been made in the unification of the electromagnetic and
weak interactions. See also elementary particles; gauge theory;
unified-field theory.
1. [The Gravitational_Interaction] some 10^40 times weaker than the
electromagnetic interaction, is the weakest of all. The force that it
generates acts between all bodies that have mass and the force is
always attractive. The interaction can be visualized in terms of a
classical field of force in which the strength of the force falls off
with the square of the distance between the interacting bodies (see
Newton's law of gravitation). The hypothetical gravitational quantum,
the graviton, is also a useful concept in some contexts. On the atomic
scale the gravitational force is negligibly weak, but on the
cosmological scale, where masses are enormous, it is immensely
important in holding the components of the universe together. Because
gravitational interactions are long-ranged, there is a well-defined
macroscopic theory in general relativity. At present, there is no
satisfactory quantum theory of gravitational interaction. Superstring
theory may give a consistent quantum theory of gravity as well as
unifying gravity with the other fundamental interactions.
2. [The Weak_Interaction] some 10^10 times weaker than the
electromagnetic interaction, occurs between leptons and in the decay
of hadrons. It is responsible for the beta decay of particles and
nuclei. In the current model, the weak interaction is visualized as a
force mediated by the exchange of virtual particles, called
intermediate vector bosons. The weak interactions are described by
electroweak theory, which unifies them with the electromagnetic
interactions.
3. [The Electromagnetic_Interaction] is responsible for the forces
that control atomic structure, chemical reactions, and all
electromagnetic phenomena. It accounts for the forces between charged
particles, but unlike the gravitational interaction, can be either
attractive or repulsive. Some neutral particles decay by
electromagnetic interaction. The interaction is either visualized as a
classical field of force (see Coulomb's law) or as an exchange of
virtual photons. As with gravitational interactions, the fact that
electromagnetic interactions are long-ranged means that they have a
well-defined classical theory given by Maxwell's equations. The
quantum theory of electromagnetic interactions is described by quantum
electrodynamics, which is a simple form of gauge theory.
4. [The Strong_Interaction] some 10^2 times stronger than the
electromagnetic interaction, functions only between hadrons and is
responsible for the force between nucleons that gives the atomic
nucleus its great stability. It operates at very short range inside
the nucleus (as little as 10^-15 metre) and is visualized as an
exchange of virtual mesons. The strong interactions are described by
quantum chromodynamics.
http://xrefer.com/entry.jsp?xrefid=488378
http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
James Allen Bressem
"Xtrchessreal" <XtrChe...@gmail.com> wrote in message
news:1169887915.0...@j27g2000cwj.googlegroups.com...
rc
> I don't want to see E=mc^2 because that just defines a process.
What process do you suppose it defines? E=mc^2 is the answer to your
question. How do you suppose Einstein came up with E=mc^2? He didn't
just pull it out of thin air, he derived it based on factors. mc^2 is
what Energy is. In the equation E=mc^2, the equality sign means equals,
literally.
What you mean to say is, 'I don't want to see E=mc^2 because I don't
understand where it comes from, and hence what it means.'
My advice is, if you want to know what Energy is intimately, follow
Einstein's reasonings from beginning until E=mc^2. Make sure that each
step makes sense to you before moving on. If you don't understand it,
study it more. It takes some time and math skills. If you don't have
them, acquire them. Start with Newtonian physics and evolve with the
science up to relativity and beyond.
Barring that, the only answer you will understand will be in general.
So, in general, there are a few ways to view Energy.
First, energy is simply a quantity that can change forms but it can be
neither created nor destroyed. So energy is always conserved.
Kinetic energy is equal to the total work that was done to accelerate a
particle from rest to its present speed. Mathematically this is
expressed in the equation K=1/2mv^2. Kinetic energy is also equal to
the total work that a particle can do in the process of being brought
to rest.
Potential Energy is energy associated with a position. It relates to
the possibility for work to be done. Gravitational potential energy for
instance is associated with a bodies weight and height above the
ground. Whereas energy stored in a deformable body such as a spring is
elastic potential energy.
We can look at a thermodynamic system as having constituent particles.
The sum of the constituent particle's kinetic energies plus the sum of
the potential energies of interaction among these particles equals the
systems internal energy.
These are just mechanical ways of regarding energy.
> We see the rocks and grass. We know what light is. Electric fields,
> Magnetic fields, are apparent by their presence and measured by Flux
> and Density etc.
>
> What is energy? Yeah we know that when electrons loose an orbital they
> emit energy...what is that?
You mean when they change orbital states? Think of it like this, they
don't just emit energy, they emit energy in the form of x. Where x can
be light, etc... Remember, energy can change forms but it can't be
created or destroyed.
At least matter has some kind of mass and velocity or acceleration.
Exactly, remember kinetic energy is 1/2mv^2, where m= mass and v = velocity.
> Is it heat? What is heat?
Heat is energy that is transferred soley because of temperature differential.
>
Chris H. Fleming
> Anyone here know what energy is?
>
> I don't want to see E=mc^2 because that just defines a process.
>
> We see the rocks and grass. We know what light is. Electric fields,
> Magnetic fields, are apparent by their presence and measured by Flux
> and Density etc.
>
> What is energy? Yeah we know that when electrons loose an orbital they
> emit energy...what is that?
Energy is the conserved quantity you get when the laws of nature have
a time shifting symmetry. That is, they are the same in the future and
in the past. Every symmetry of the laws of nature has an associated
conserved quantity.
> At least matter has some kind of mass and velocity or acceleration. Is
> it heat? What is heat?
Heat is a kind of energy that comes up in thermodynamics. Basically,
when you aren't exactly conserving work-energy, the deficit is some
kind of heat.
rc
<chris_h...@yahoo.com> said:
> Heat is a kind of energy that comes up in thermodynamics. Basically,
> when you aren't exactly conserving work-energy, the deficit is some
> kind of heat.
I see what you mean, but I'm posting this because the person who asked
the original question obviously doesn't have a basis from which to give
you charity.
Heat is an energy. Specifically, its refers to energy in transit
between bodies or systems because of a temperature difference.
Heat and temperature are different. Consider that if you cut an object
in half, both halves are the same temperature as the whole. If we want
to raise the temperature of the halves by a given amount though, it
will require only half as much heat as it did for the whole. With this
in mind, heat is commonly used in terms of "The heat needed to change
the temparature of x object to x degrees." Strictly speaking energy is
always conserved, it is never not exactly conserved.
tooly
"AE" <hid...@nospam.com> wrote in message
news:epfpre$ufa$01$1...@news.t-online.com...
Thanks AE. "what is mass, electric field...etc etc" required an answer...as
'energy' per se, IS different for it is perhaps the fundamental building
block of all the others, but as you say, while having no object itself.
Justintruth
> Potential Energy is energy associated with a position. It relates to
> the possibility for work to be done. Gravitational potential energy for
> instance is associated with a bodies weight and height above the
> ground. Whereas energy stored in a deformable body such as a spring is
> elastic potential energy.
>
One of the things that helped me understand energy in classical
mechanics was to realize its realtionship to two properties of vector
fields called the divergence and the curl.
I am going to be very imprecise but hopefully it will give you the
gist of what I mean.
Basically a "force field" can be though of as an "arrow" attached to
each point of space. If you put something there it will experience a
"force" in the direction the arrow points and, if the arrrow is
longer, the force will push harder.
Now you can imagine many kinds of force fields. Two are very useful to
see what energy really means in classical mechanics.
The first is a force field that goes outward at every point from some
central point. So all of the arrows point away from some center point
or "particle". The size of the arrows get smaller as you move away by
1/r^2 which makes sense because the effect of the force is distributed
over more and more area. If you draw one of these force fields on a
paper you can see visually that the arrows "diverge" from that center
point. Mathemeticians would say that the center point has
"divergence".
Another field that is useful to look at is a force field that goes
around and around. Imagine that there are concentric circles around
some point and each arrow is tangent to those circles. The arrows in a
sense "curl" around the point. Mathemeticians would say the center of
the circles has "curl".
Now the key to see the relation to energy is to see how these force
fields act. For example lets take the "curled" field. Imagine I put a
particle down somewhere. What would happen is that it would be
accelerated around and around. It would go faster and faster and
spiral away from the center. There is a quantity 1/2 m*v^2 which is
"accumulated" as a force acts over a distance. In this kind of a force
field that quantity would get higher and higher and higher as the
particle spiraled out. However if you applied another force to keep
it on a circle, like a string that holds a ball in when you swing it,
then it could go around the circle and be back where it was at the
start. But it would be going faster. The particle would then go around
again and would be going even faster. The process of going faster and
faster would continue and energy would always increase.
Now look at the "divergent" vector field. It turns out that if you
placed a particle a little off center it would move outward faster and
faster.Again the force acting over a distance would constantly
increase the velocity (although suprisingly the velocity would have a
limit that it would never reach- but that is another story). If you
put a wall up and the partical bounced off the wall and started going
back at the same velocity toward the center of the field where it came
from, it would start to slow down and it turns out that it would come
to rest exactly where it started and then repeat the process. This can
be imagined like a ball rolling off of a hill and up another one where
it stops and then rolls back down and back up to where it was and then
repeats. It turns out that wilth this kind of a force field you could
always tell how fast the ball is going just by looking at the height
of the ball on the hill. Because when it goes down it always goes
faster based on how far down it went independent of the path that it
took in going down. A steep hill or a shallow one would result in the
same speed of the ball at a given height (assuming they started at the
same speed and same height). A ball could not end up back in the same
place moving faster. At any point it would always have the same speed
that it had the last time it was at that point.
Therefore in the second case you can define a number called the energy
of the ball. It is sort of like a measure of how high it could go on
its own before it would completely stop and roll back down (unless it
exactly balanced on the top of a hill). As the ball moves up we say
its potential energy (the energy that is dependent on its height)
increases and its kinetic energy (the energy that is dependent on its
velocity) decreases. As the ball moves down the potential energy
decreases and the kinetic energy increases. However, the sum of
potential and kinetic energy remains the same and at any given height
the ball will have a given velocity in such a way that when you add
the energy due to height to the energy due to speed you would always
get the same number. More height less speed. More speed less height.
But the sum of these "quantites" (the force * height and 1/2 mass *
velocity^2) (potential +kinetic energies) would be the same number.
So for a force field that has a "curl" it turns out energy isn't
conserved and something will go faster and faster. But if the field
has zero curl and is basically like a bunch of hills with a ball
rolling around on it, then the ball will have a quantity that stays
the same called "energy". That energy will switch back and forth
between potential and kinetic depending on how the ball is rolled. It
turns out that most (maybe all) force fields in nature have zero curl.
You can then think of a spring. Imagine pulling it out and then
letting it go. It will "fall" inwards and pass the point where it
would be at rest and then compress and then expand again and it is
like a ball on the hill. At the extremes of compression and expansion
the spring comes to rest for a moment. At that point it has
"potential" energy and then the spring starts moving and at the
"equilibrium" where the spring is neither compressed or uncompressed
it will be moving fast and has "kinetic" energy.
The same thing with someone on a swing. At the height they have
potential energy and at the bottom kinetic.
Also a satellite. Its orbit has a high point called apogee and a low
point called perigee. It will go faster at perigee because its height
has been lowered and now the potential energy has been turned into
kinetic energy.
The problem in a spring is that it is made up of atoms and eventually
all of the energy gets them vibrating in random directions. They are
still going from potential to kinetic but over tiny distances and it
looks like the spring has come to rest but in reality at a molecular
level it is vibrating. That "energy" has become "heat" which means it
has become microscopic and in radom directions. It seems to run down
or "dampen" but in reality it is just that the motion is becoming
microscopic. And so you can sometimes add heat into the equation.
When Einstein did relativity theory he found out that the "mass" of a
object increased as it was accelerated. That lead to a change in the
"classical" theory of energy and E=mc^2 came about. (BTW in the right
units the equation is E=M). Also Eienstein showed that part of what
one observer saw as "energy" would not be "energy" for another moving
relative to the first. He greated a "momentum energy fourvector" and
latter a "stress energy momentum tensor" which are the descendents of
the classical concept of energy. My understanding is that in General
relativity there really is no notion of conservation of energy
strictly speaking although I am still trying to understand that
theory.
Hope it helps. I also wonder what "energy" is.
One thing for sure. It is not something hokey. It is a concept that
has a precise mathematical definition relative to the equations of
motion that are used in physics.
The above "explanation" is very imprecise and in some ways misleading.
It would be better to learn the equations to see what energy really
means.
andy-k
<snip>
> The above "explanation" is very imprecise and in
> some ways misleading. It would be better to learn
> the equations to see what energy really means.
I haven't come across such nice down-to-earth explanations
of div and curl. Books on vector analysis usually skip the
bottom level and dive straight into the abstractions.
tg
On Jan 29, 7:09 am, "andy-k" <spam.free@last> wrote:
> "Justintruth" wrote:<snip>
>
> > The above "explanation" is very imprecise and in
> > some ways misleading. It would be better to learn
> > the equations to see what energy really means.I haven't come across such nice down-to-earth explanations
> of div and curl. Books on vector analysis usually skip the
> bottom level and dive straight into the abstractions.
Except that we now have the question: What is a 'force field'? (Star
Trek aside.)
There is a good reason for the lack of "down to earth" explanations---
we are talking exactly about abstractions, and confusion like the OP's
arises from not understanding that.
-tg
andy-k
> "andy-k" wrote:
>> I haven't come across such nice down-to-earth explanations
>> of div and curl. Books on vector analysis usually skip the
>> bottom level and dive straight into the abstractions.
>
> Except that we now have the question: What is a 'force field'?
> (Star Trek aside.)
>
> There is a good reason for the lack of "down to earth"
> explanations--- we are talking exactly about abstractions,
> and confusion like the OP's arises from not understanding that.
I appreciate what you're saying tg, but that is something that is
best understood from a higher perspective. When math isn't one's
strong point, there needs to be some way of getting a foothold
at the bottom of the rockface in order to begin the ascent at all.
Even if there may be some ambiguities, such ambiguities may be
skillfully used in order to ascend to the level where disambiguation
becomes necessary. I think that many physicists miss this point
because they have no problem with the math to begin with, and
can't get down to my level of ignorance in order to point the way.
(And having failed to elucidate such fundamentals, lecturers then
proceed to throw the poor students straight into Maxwell's equations!)
Justintruth
what a "field" is.
Again being imprecise....
FIrst "Force":The simplest way to look at it is to take your hand and
push on something. What you are doing is "applying a force" to the
object. A "force" "makes things accelerate" which means it changes the
thing from not moving to moving or changes the motion from moving to
not moving such as when a shopping cart is comming at you and you push
on it to stop it. Force changes the velocity of something. The real
trick of it is to see how Newtons law "defines" force. Newtons law
says "A body in motion tends to stay in motion a body at rest tends to
remain at rest". What that really meant was that as far as he was
concerned (from that day forward he would think of it this way)
nothing was required to "explain" what a body that is "at rest" stayed
"at rest" and that nothing was required to "explain" why a body "in
motion" stayed "in motion" it just "tended to". However if a body at
rest were somehow "speeded up" or a body in motion (having one
velocity) were either "speeded up" or "slowed down" then that would
require something to explain why... what he called a "force" acting on
it - it would require a force to "cause" the speedup or slowdown. So
basically whenever something is speeded up or slowed down there must
be a "force" doing it.
That was just his theory, his "way of looking at it" and it worked
amazingly well. This was just his "way of looking at things" or his
"theory", but if you think like he did then you can explain a lot of
things.
There is one subtlety. The "speed" of an object is how fast it is
going (relative to something). So for a car on a highway it is like 55
miles an hour. However, in physics they use the term "velocity" which
is speed in a given direction. So a car going north at 55 miles/hour
has the same speed as a car going south at 55 miles per hour but the
velocity is not the same because the direction is opposite. So speed
is a number but velocity is an arrow (basically a number and a
direction) They use the term "vector" instead of "arrow" sometimes but
it is the same thing. It turns out that whenever the "velocity"
changes then there is a force that changes it. So, if I have a
satellite and it is orbiting the earth at the same speed all the time
in a big circle, then there is still a change in the direction of the
speed as it goes around and so there is still a force (gravity in this
case) that causes the change in velocity.
If you take a spring an stretch it and connect one end to one thing
and another end to another thing each thing will pull on the other and
when you let them go they will not stay at rest they will "accelerate"
meaning thier velocity will increase towards each other. This is an
example of forces being "equal and opposite". It turns out that the
objects, if they are identical to each other will accelerate toward
each other at the same rate of acceleration. But if one object is
twice as big as the other and made of the same stuff then the big one
will accelerate toward the small one slower than the small one
accelerates toward the bigger. You could say one pulled harder on the
other but Newton said no. He said lets assume they are pulled on just
as hard (the spring is the same spring after all) but that one thing
has a property that is different than the other (which made sense
because if they are the same material one is bigger than the other!)
He calle the property mass. So what Newton did was imagine a
"standard" thing. He then imagined hooking all kinds of things too it
with a spring (for example) and seeing how they accelerate. If they
accelerate the same then he said they have the same "mass" as the
standard mass if they accelerate twice as slow then they have twice
the mass (of that standard mass) half as slow and they have half the
mass. The mass is therefore a ratio of accelerations relative to a
standard mass. The equation was then Force=mass * acceleration. Which
is true because that is how you find the mass in the first place. If
you hook anything to a standard mass and it accelerates twice as slow
toward the standard mass as the standard mass does toward it then it
is twice as "massive" so of course Force = mass * acceleration since
he assumed (in another law) that the forces were always equal and
opposite.
So basically you can think of a force as an arrow that accelerates
things. If the thing is less massive the same force (same arrow) will
accelerate them more and if it is more massive then the same force
(same arrow) will accelerate them less. So if you push the same
strength on a block of lead it will accelerate less than if you push
just as hard on a block of styrofoam.
So force is represented by and "arrow" that shows the direction you
mean to push and then a size (the length of the arrow) that shows how
hard you are pushing. Interesting that if you push on one side and
just as hard on the other side then the forces cancel and nothing
moves.
So much for "Force" now what is a "Field". A "field" is sort of like
this: Imagine a field of corn. Each "place" in the field has a corn
stalk that has so many ears of corn on it. So you have a relationship
between the place and something else called the corn. It is a corn
field. Well a force field is a lot like that. Imagine space and at any
point in space imagine there is a force (arrow) at that point. Then in
physics they say there is a "force field" around the point. That is
all it means basically. At every point in space there is an arrow. Its
a field of arrows. A force field of force arrows or a "force field"
for short.
For example take the earth. Basically there is a "gravitational force
field" around it. That means that at any point in the space around the
earth you can put an arrow which will show how a mass will "be
accelerated" both in direction and in amount of acceleration if you
"dropped" it (let it go). If the earth was a perfect sphere all of the
arrows would point toward the center of the earth. Then the
gravitational force field would have no "curl" it would only have
"divergence" and in that force field we could define the energy of
anything moving in it and as it moved up or down the energy would stay
the same changing from potential when higher to kinetic when lower.
So we could then watch a bouncing ball in the "gravitational force
field". As it goes up it is slowed down by the force of gravity until
it reaches the top and then it starts back down. At any point however
if you measured the kinetic energy and the potential energy they would
be the same. That's really why the physicists define it. Because I can
just look at how high it started at and as it falls I can tell you
what its speed is at any height because "independent of the path" the
thing took the energy is conserved. It can make the calculations a lot
easier to do. If I know how fast a satellite is going at appogee (its
highest point) then I can calculate its energy. Then you pick any
point in the orbit and tell me how high it is and I can calculate how
much kinetic energy it now must have and then give you its velocity.
That is why it is a useful concept when doing these calculations.
The really hard thing to get your mind around is that the force field
goes on infinitely but it gets weaker and weaker and it turns out that
there is a speed which if you throw the ball up it will start going
slower and slower and at any time in the future you can look at its
velocity and if you look latter it will have a slower velocity but it
will never go to zero. That speed which, if you throw something up at
it then it will never return, is called the escape velocity. The
strange thing is that if you have a sum with an infinite number of
terms you would think the sum would be infinite. Like sum=a1 + a2 + a3
+ .... for ever infinitely should be infinite. The sum you would
think would be infinite. But, if each term gets smaller and smaller
then it turns out it is not infinite.
For example if you stand 10 feet from a wall and then go 5 feet and
then 2.5 feet and then 1.25 feet and keep doing that and make a sum:
sum=5+2.5+1.25+.625... forever infinitely... it turns out the sum is
10 feet even though the number of terms is infinite. In the same way
even though gravity goes on infinitely it has a finite effect because
it gets weaker and weaker.
Later on Einstein redefined what Newton had done. He changed the rule
that said "A body in motion...." by changing what was meant by "being
in motion". In his physics something that falls was moving on a
special curved line called a "geodesic" and only if a thing deviated
from that line would their be a "force". So there is no "gravitaional
force field" in his theory.
It really is amazing. Those guys who think these things up, like
Newton and Einstein, are really amazing.
On Jan 29, 8:33 am, "tg" <tgdenn...@earthlink.net> wrote:
> On Jan 29, 7:09 am, "andy-k" <spam.free@last> wrote:
>
> > "Justintruth" wrote:<snip>
>
> > > The above "explanation" is very imprecise and in
> > > some ways misleading. It would be better to learn
> > > the equations to see what energy really means.I haven't come across such nice down-to-earth explanations
> > of div and curl. Books on vector analysis usually skip the
> > bottom level and dive straight into the abstractions.Except that we now have the question: What is a 'force field'? (Star
Wanker
On 27 Jan, 08:51, "Xtrchessreal" <XtrChessr...@gmail.com> wrote:
> Anyone here know what energy is?
energy
1599, from M.Fr. energie, from L.L. energia, from Gk. energeia
"activity, operation," from energos "active, working," from en- "at" +
ergon "work" (see urge (v.)). Used by Aristotle with a sense of "force
of expression;" broader meaning of "power" is first recorded in Eng.
1665. Energize "rouse to activity" is from 1753; energetic of persons,
institutions, etc., is from 1796. Energy crisis first attested 1970.
(cf. http://www.etymonline.com/index.php?
search=energy&searchmode=none)
heat
O.E. hætu, hæto, from P.Gmc. *khaitin- "heat," from *khaitaz
"hot" (cf. O.S. hittia, O.N. hiti, O.Fris. hete, Ger. hitze "heat,"
Goth. heito "fever"). The same root is the source of O.E. hat "hot"
and hæða "hot weather." The verb is from O.E. hætan, from P.Gmc.
*khaitijanam. Meaning "a single course in a race" is from 1663,
perhaps from earlier fig. sense of "a single intense effort" (c.1380),
or meaning "run given to a horse to prepare for a race" (1577).
Meaning "sexual excitement in animals" is from 1768. Meaning "trouble
with the police" attested by 1920. Heat wave "period of excessive hot
weather" first attested 1893. (cf http://www.etymonline.com/index.php?
search=heat&searchmode=none)
> X
So that's what heat and energy are.
If what you really mean is "What's the common factor between heat,
energy, electrons and so forth" then what you want is physics, unless
you've already decided that there must be one common factor between
all of them, in which case you need philosophical therapy.
Justintruth
do the equations trough rote memory but I just could not understand
why they called it "curl" or "divergence". I really wished they had
just drawn a picture on a blackboard. It took me years to understand
and its really simple. I guess they just thought I knew. If I was a
physics teacher I would always include a question like "Why do they
call it the curl?" in my final. That's the problem I have with
relativity also. They go through the equations but its really hard
sometimes to get what they are even talking about without pictures. I
think they need a lot more pictures in the textbooks. Or even
better, .avi files or some sort of animation. It could be made a lot
easier to learn that way.
On Jan 29, 7:09 am, "andy-k" <spam.free@last> wrote:
> "Justintruth" wrote:<snip>
>
> > The above "explanation" is very imprecise and in
> > some ways misleading. It would be better to learn
> > the equations to see what energy really means.I haven't come across such nice down-to-earth explanations
tg
On Jan 29, 10:31 am, "andy-k" <spam.free@last> wrote:
> "tg" wrote:
> > "andy-k" wrote:
> >> I haven't come across such nice down-to-earth explanations
> >> of div and curl. Books on vector analysis usually skip the
> >> bottom level and dive straight into the abstractions.
>
> > Except that we now have the question: What is a 'force field'?
> > (Star Trek aside.)
>
> > There is a good reason for the lack of "down to earth"
> > explanations--- we are talking exactly about abstractions,
> > and confusion like the OP's arises from not understanding that.I appreciate what you're saying tg, but that is something that is
> best understood from a higher perspective. When math isn't one's
> strong point, there needs to be some way of getting a foothold
> at the bottom of the rockface in order to begin the ascent at all.
> Even if there may be some ambiguities, such ambiguities may be
> skillfully used in order to ascend to the level where disambiguation
> becomes necessary. I think that many physicists miss this point
> because they have no problem with the math to begin with, and
> can't get down to my level of ignorance in order to point the way.
> (And having failed to elucidate such fundamentals, lecturers then
> proceed to throw the poor students straight into Maxwell's equations!)
In the Subject and Object thread, you talked about "the experience" of
an electron. I think that's an excellent point and well developed in
your paragraph. Why can't we say to people that a field is a
representation of what an electron experiences, but that it is in
effect a *subjective* experience?---it is no more accessible to our
sensual paradigm than what a dog smells when it sniffs your crotch.
It is the attempt to create analogies to our physical experiences that
creates the confusion as far as I can tell. Remember, the language of
fields follows the language of fluid dynamics. Is there a fluid? Well,
working on magnetic fields one might very well come to internalize and
visualize problems as if there were, but when the job changes, that
sense is discarded. I'd like people to understand that, rather than
think that any of our analogies are 'reality'.
-tg
Wanker
On 29 Jan, 13:33, "tg" <tgdenn...@earthlink.net> wrote:
> On Jan 29, 7:09 am, "andy-k" <spam.free@last> wrote:
>
> > "Justintruth" wrote:<snip>
>
> > > The above "explanation" is very imprecise and in
> > > some ways misleading. It would be better to learn
> > > the equations to see what energy really means.I haven't come across such nice down-to-earth explanations
> > of div and curl. Books on vector analysis usually skip the
> > bottom level and dive straight into the abstractions.
> Except that we now have the question: What is a 'force field'? (Star Trek aside.)
This question is (in this context) exactly the same as the question
"What sense shall we give the expression 'force field'?"
IOW - it means what you want it to mean because it doesn't already
have a well-defined meaning, even though it has several commonly-
understood meanings, such as:
"A region of space throughout which the force produced by an agent or
several agents, such as an electric charge, is operative."
"The space around a radiating body within which its electromagnetic
oscillations can exert force on another similar body not in contact
with it"
or even
"A human-invisible barrier under the control of the USS Enterprise
which aims to prevent harmful phenomena entering that spaceship."
> There is a good reason for the lack of "down to earth" explanations---
> we are talking exactly about abstractions, and confusion like the OP's
> arises from not understanding that.
There aren't any down to earth explanations for the same reason as the
action of pointing at an object's shape, colour or size won't in and
of itself tell you which of the above was being pointed at.
> -tg
ck
> Anyone here know what energy is?
>
> I don't want to see E=mc^2 because that just defines a process.
>
> We see the rocks and grass. We know what light is. Electric fields,
> Magnetic fields, are apparent by their presence and measured by Flux
> and Density etc.
>
> What is energy? Yeah we know that when electrons loose an orbital they
> emit energy...what is that?
>
> At least matter has some kind of mass and velocity or acceleration. Is
> it heat? What is heat?
>
> X
>
I would say energy exist in the potential between one state and another.
It a measure of differance, the motion which occurs between differing
bodies.
tg
On Jan 29, 10:53 am, "Justintruth" <truth.jus...@gmail.com> wrote:
> I agree. I got an "A" in electricity an magnetism in college. I could
> do the equations trough rote memory but I just could not understand
> why they called it "curl" or "divergence". I really wished they had
> just drawn a picture on a blackboard.
You took an E and M course and there were no pictures in the
textbook? Did you ever open it?
-tg
andy-k
> "andy-k" wrote:
>> "tg" wrote:
>>> Except that we now have the question: What is a 'force field'?
>>> (Star Trek aside.)
>>
>> > There is a good reason for the lack of "down to earth"
>> > explanations--- we are talking exactly about abstractions,
>> > and confusion like the OP's arises from not understanding that.
>>
>> I appreciate what you're saying tg, but that is something that is
>> best understood from a higher perspective. When math isn't one's
>> strong point, there needs to be some way of getting a foothold
>> at the bottom of the rockface in order to begin the ascent at all.
>> Even if there may be some ambiguities, such ambiguities may be
>> skillfully used in order to ascend to the level where disambiguation
>> becomes necessary. I think that many physicists miss this point
>> because they have no problem with the math to begin with, and
>> can't get down to my level of ignorance in order to point the way.
>> (And having failed to elucidate such fundamentals, lecturers then
>> proceed to throw the poor students straight into Maxwell's equations!)
>
> In the Subject and Object thread, you talked about "the experience"
> of an electron. I think that's an excellent point and well developed
> in your paragraph. Why can't we say to people that a field is a
> representation of what an electron experiences, but that it is in
> effect a *subjective* experience?---it is no more accessible to our
> sensual paradigm than what a dog smells when it sniffs your crotch.
I like this -- it puts me in mind of a Leibnizian view of the world.
> It is the attempt to create analogies to our physical experiences that
> creates the confusion as far as I can tell. Remember, the language of
> fields follows the language of fluid dynamics. Is there a fluid? Well,
> working on magnetic fields one might very well come to internalize and
> visualize problems as if there were, but when the job changes, that
> sense is discarded. I'd like people to understand that, rather than
> think that any of our analogies are 'reality'.
Your point is well made. The most obvious case is the Quantum Theory
-- best admired from a distance by the mathematically challenged like
myself. I recall being fascinated by the introductory course describing the
historical necessity for a new paradigm, but in a subsequent course getting
hopelessly lost in all that eigenvector and eigenvalue stuff. Dirac's own
book (where he describes his bra and ket nomenclature) gave me the
feeling that he was working at a high level of abstraction in order to avoid
all the implicit misunderstandings that accompany our propensity to create
analogies to our physical experiences, but that in doing so, he'd deprived
the novice of any means of getting a foothold. Like trying to climb a glass
wall.
tg
You have a dog named Leibniz?
>
> > It is the attempt to create analogies to our physical experiences that
> > creates the confusion as far as I can tell. Remember, the language of
> > fields follows the language of fluid dynamics. Is there a fluid? Well,
> > working on magnetic fields one might very well come to internalize and
> > visualize problems as if there were, but when the job changes, that
> > sense is discarded. I'd like people to understand that, rather than
> > think that any of our analogies are 'reality'.
>Your point is well made. The most obvious case is the Quantum Theory
> -- best admired from a distance by the mathematically challenged like
> myself. I recall being fascinated by the introductory course describing the
> historical necessity for a new paradigm, but in a subsequent course getting
> hopelessly lost in all that eigenvector and eigenvalue stuff. Dirac's own
> book (where he describes his bra and ket nomenclature) gave me the
> feeling that he was working at a high level of abstraction in order to avoid
> all the implicit misunderstandings that accompany our propensity to create
> analogies to our physical experiences, but that in doing so, he'd deprived
> the novice of any means of getting a foothold. Like trying to climb a glass
> wall.
I am hardly a defender of how math is taught at all levels and within
disciplines like physics. We have software now that would eliminate
90% of the the things that turn people off.
The claim that you only 'understand' something like QM if you have
worked through the math is simply the result of the effect I mentioned
about internalizing a model and dealing with it as reality. If you
work through the math, you understand it the way people who have
worked through the math understand it. Which of course is what
physicists do. However, as you were taught in that first course,
breakthroughs happen when people *stop* understanding things the way
they learned.
-tg
andy-k
> "andy-k" wrote:
>> "tg" wrote:
>> > In the Subject and Object thread, you talked about "the experience"
>> > of an electron. I think that's an excellent point and well developed
>> > in your paragraph. Why can't we say to people that a field is a
>> > representation of what an electron experiences, but that it is in
>> > effect a *subjective* experience?---it is no more accessible to our
>> > sensual paradigm than what a dog smells when it sniffs your crotch.
>
>>I like this -- it puts me in mind of a Leibnizian view of the world.
>
> You have a dog named Leibniz?
Now *there's* a good name for my new pup!
I could call him "nits" for short.
>>Your point is well made. The most obvious case is the Quantum Theory
>> -- best admired from a distance by the mathematically challenged like
>> myself. I recall being fascinated by the introductory course describing
>> the historical necessity for a new paradigm, but in a subsequent course
>> getting hopelessly lost in all that eigenvector and eigenvalue stuff.
>> Dirac's own book (where he describes his bra and ket nomenclature)
>> gave me the feeling that he was working at a high level of abstraction in
>> order to avoid all the implicit misunderstandings that accompany our
>> propensity to create analogies to our physical experiences, but that in
>> doing so, he'd deprived the novice of any means of getting a foothold.
>> Like trying to climb a glass wall.
>
> I am hardly a defender of how math is taught at all levels and within
> disciplines like physics. We have software now that would eliminate
> 90% of the the things that turn people off.
>
> The claim that you only 'understand' something like QM if you have
> worked through the math is simply the result of the effect I mentioned
> about internalizing a model and dealing with it as reality. If you
> work through the math, you understand it the way people who have
> worked through the math understand it. Which of course is what
> physicists do. However, as you were taught in that first course,
> breakthroughs happen when people *stop* understanding things the way
> they learned.
Sure -- it's just that the math is needed to describe things that go on in
our physical experiences rather than being a stand-alone enterprise (math
for math's sake), but in the case of QM the connection seems to get lost
somewhere, as though our physical experiences were the wrong place to
start and we only stumbled across the right place to start by serendipity.
Reminds me of an old joke about a stranger passing through a village in
Ireland and asking one of the yokels the direction to Galway, and the yokel
replies "If I wanted to get to Galway, I wouldn't have started from here!"
tg
On Jan 29, 2:48 pm, "andy-k" <spam.free@last> wrote:
> "tg" wrote:
> > "andy-k" wrote:
> >> "tg" wrote:
> >> > In the Subject and Object thread, you talked about "the experience"
> >> > of an electron. I think that's an excellent point and well developed
> >> > in your paragraph. Why can't we say to people that a field is a
> >> > representation of what an electron experiences, but that it is in
> >> > effect a *subjective* experience?---it is no more accessible to our
> >> > sensual paradigm than what a dog smells when it sniffs your crotch.
>
> >>I like this -- it puts me in mind of a Leibnizian view of the world.
>
> > You have a dog named Leibniz?Now *there's* a good name for my new pup!
Well, I understand that I may be different in how I see these things.
I don't find
QM mysterious, or at least not any more mysterious than charge for
example. And in my conception of things, the idea that there is a
'some-thing' and that it has a 'position' that is equivalent to the
abstraction called a 'point in space' is pretty spooky. For lots of
people in the world, indeterminacy is just the way things are, and
they never heard of QM at all.
-tg
andy-k
> Well, I understand that I may be different in how I see these things.
> I don't find QM mysterious, or at least not any more mysterious than
> charge for example. And in my conception of things, the idea that there
> is a 'some-thing' and that it has a 'position' that is equivalent to the
> abstraction called a 'point in space' is pretty spooky. For lots of people
> in the world, indeterminacy is just the way things are, and they never
> heard of QM at all.
"Shut up and calculate"? Didn't Feynman also say that
"If a person isn't baffled by quantum mechanics,
then that person doesn't understand quantum mechanics"?
rc
> My understanding is that in General
> relativity there really is no notion of conservation of energy
> strictly speaking although I am still trying to understand that
> theory.
There is a notion of it, its just generalized into the mass-energy
conservation law. Conservation of mass and conservation of energy,
which developed independantly from one another, are actually both cases
of this broader conservation principle. Einstein saw that in order to
maintain conservation of momentum and energy the equations regarding
momentum, kinetic energy and Newtons Second Law had to be generalized.
This generalization leads to the concept of rest energy. As I
understand it, this is experimentally proven by particle
transformations. A neutral pion for instance has no kinetic energy
before decay. As it decays EM radiation appears. The EM radiation that
appears corresponds to the rest mass that disappeared. The total energy
of the EM radiation after decay is equal to mc^2 exactly. This
generalized principle of conservation is how a nuclear plant generates
power. When uranium undergoes fission, the rest mass of the fragments
is less than the rest mass of the parent nucleus. The energy released
used to turn the turbines is equal to the decrease in mass multiplied
by c^2.
> Hope it helps. I also wonder what "energy" is.
Energy is everything and everything is energy. Even things with no
mass, such as photons, can be regarded in terms of energy provided they
travel at light speed.
> One thing for sure. It is not something hokey.
> It is a concept that
> has a precise mathematical definition relative to the equations of
> motion that are used in physics.
> It would be better to learn the equations to see what energy really
> means.
"What does energy mean?" doesn't bother me near as much as "what does
meaning mean?".
I assume that when the question "what does energy mean?" is raised, a
pragmatic answer is called for. I then access the extent of my
knowledge and express it using words. The whole while, no matter how
thorough my explanation, it seems to fall short of "what energy means".
As you say, it does have a precise mathematical definition, but math is
just another language like english, or chinese.
Is that ...hokey :)
rc
> You have a dog named Leibniz?
I have a dog with one testicle named monad.
> I am hardly a defender of how math is taught at all levels and within
> disciplines like physics. We have software now that would eliminate
> 90% of the the things that turn people off.
>
> The claim that you only 'understand' something like QM if you have
> worked through the math is simply the result of the effect I mentioned
> about internalizing a model and dealing with it as reality. If you
> work through the math, you understand it the way people who have
> worked through the math understand it. Which of course is what
> physicists do. However, as you were taught in that first course,
> breakthroughs happen when people *stop* understanding things the way
> they learned.
>
> -tg
Well stated. Math is a language, and thats all. For that matter, I
don't really think people are 'bad' at math, they just don't like to
study it because its rules are black and white. People hate to hear
'your wrong'. When I go through equations with someone, I treat it like
a conversation. I try not to say 'your wrong'. I try to say 'I don't
agree'. At that point we can't move on until we both agree.
Breathroughs happen in math, as you say, because we don't usually think
in terms of math. When we understand a concept mathematically we have a
*wow* moment because it is literally a new way of understanding the
concept. This should never be misunderstood as the *only* way, or the
*right* way to understand a concept.
Physicists live in Physicsland; and in physics land they speak math. If
you want to visit Physicsland, you should learn some basic phrases at
least, or you won't benefit as much as you could. When someone asks
'what does energy mean?' I take it they want the definition from
Physicsland because that, in my opinion, is the most pragmatic
definition. In Metaphysicsland they pronounce energy like this :
'soaaal', but they also have alot of different dialects over there.
tg
Well, he also co-authored a paper on time-reversed particles. Which
tells me that he realized that where he was wasn't the only place he
could be.
-tg
Justintruth
"Because spacetime is curved there is no well defined notion of
vectors at different points being parallel; parallel transport is
curve dependent. Thus, there is no natural "global family" of inertial
observers, and a given observer cannot, in general, define the energy
of a distant particle...... the argument fails that the equation
delaTab=0 (Tab is the stress energy momentum tensor) implies strict
energy conservation."
He attributes this to the fact of tidal gravitation.
So, I do not think that the stress energy momentum tensor results in a
global law of conservation of energy like there is in special
relativity. My understanding is that energy is not conserved in the
universe according to general relativity. I emphasis that I have read
this and am trying now to understand it. I do no yet understand it
mathematically on my own. I do understand his comment on "path
dependence".
In my opinion classical energy conservation is based on the fact that
the curl of the force fields are zero. However this physics was done
on a flat manifold. In general relativity the manifold is not "flat"
and so if you displace a vector in a curve it will not return as the
same vector. If I take a vector on the plane and move it in a square
it will come back to the same vector but not if I do it on a sphere.
Consider moving a vector from the north poll south to the equator and
the 90 deg along the equator and then back to the north pole. The
result is a 90 deg rotation of the vector. So I think that his point
is the same only with the stress mass energy tensor being displaced.
Two different paths to the source and you have two different vectors.
Energy is not conserved.
With respect to the meaning of meaning I get your point.
It seems to me that some of the most meaningful things are those that
are least defined and I do not think that lack of definition implies
lack of meaning - or rigour. I think, however, that "energy" in the
scientific sense is well defined. I think of "definition" as the
process of "limiting the meaning at its boundary". With adequate
definition the meaning becomes more exact and gets distinguished from
other meanings which, without the defintion, would cause
equivocation.
For example, I often see metaphysical statements confused with
physical statements when it comes to the term "energy". The writings
often will confuse an experience of being with an experience of "the
universe" which is interpreted as "being energy". You will then hear
things like "that place had good energy" and really, the person is so
confused, that they think that what they are calling "good energy" is
in fact what scientists refer to as "energy". They are not the same
albeit they are related.
I think that the relation is because and "energyless" particle would
not interact with any instruments and so physically would not exist.
So I think the idea of energy becomes confused with the idea of
material existence which then becomes further equivocated with
existence itself. In my opinion it is better to precisely define
energy as a physical term and make it distinct from the metaphysics of
Being.
This I think is why cosmology and religion always get mixed up. I
personally don't think they are related. I guess that is what I mean
by "hokey". Whenever physics is confused with metaphysics a type of
fundamentalism occurs which is IMO destructive of real understanding.
I therefore prefer to "define" the term energy mathematically as a
submeaning under the general physical sciences understanding that this
does not invalidate metaphysics but rather distinguishes it from
"natura" or "physics".
Don't you agree?
On Jan 30, 2:46 am, rc <nos...@gmail.com> wrote:
> On 2007-01-29 05:26:34 -0600, "Justintruth" <truth.jus...@gmail.com> said:
>
> > My understanding is that in General
> > relativity there really is no notion of conservation of energy
> > strictly speaking although I am still trying to understand that
> > theory.There is a notion of it, its just generalized into the mass-energy
> conservation law. Conservation of mass and conservation of energy,
> which developed independantly from one another, are actually both cases
> of this broader conservation principle. Einstein saw that in order to
> maintain conservation of momentum and energy the equations regarding
> momentum, kinetic energy and Newtons Second Law had to be generalized.
> This generalization leads to the concept of rest energy. As I
> understand it, this is experimentally proven by particle
> transformations. A neutral pion for instance has no kinetic energy
> before decay. As it decays EM radiation appears. The EM radiation that
> appears corresponds to the rest mass that disappeared. The total energy
> of the EM radiation after decay is equal to mc^2 exactly. This
> generalized principle of conservation is how a nuclear plant generates
> power. When uranium undergoes fission, the rest mass of the fragments
> is less than the rest mass of the parent nucleus. The energy released
> used to turn the turbines is equal to the decrease in mass multiplied
> by c^2.
>
> > Hope it helps. I also wonder what "energy" is.Energy is everything and everything is energy. Even things with no
Justintruth
>You took an E and M course and there were no pictures in the textbook? Did you ever open it?
>
Yea, I opened it. I studied it for years. In the end the pages were
worn out and the bindings were broken. It took me more than 10 years
to get through it and there are still some aspects that I don't get.
For example I think that the Euler characteristic of a manifold should
have some effect on electricity and magnetism and I am trying to
understand that still.
But what was disapointing was that the result of all that time...it
seemed most of it was wasted in retrospect... it seemed that if there
had been like a slide show instead of text... then the result would
have beed obtained easier. I feel that a lot of the time was wasted
because the understanding I got banging my head against the wall could
have been done easier with lots of pictures. I think I could teach it
a lot faster than I learned it.
I don't think it would have been a little easier with lots of
pictures, I think it would have been a lot easier with lots of
pictures.
I spoke to someone who worked on the math curicula for California once
about it. She told me that was exactly what they had found with
teaching things like square root etc to children. If it is does with
the geometry as a companion to the artitmetic it becomes much easier
to see. As for myself I didn't even realize until after college that
"sq meters" were really square meters. It might seem obvious but some
of us are... challenged.
I was very hung up on covarient and contravarient vectors until I
understood there relationship to the geometry of a paralellogram.
There are a lot of examples.
Justintruth
intuitiveness" of the theory of relativity and a "lack of
imaginability" of how things are. It is the absence of a geometrical
"picture" of the universe, a picture which, if it existed, would
constitute a priveleged frame of reference that causes the perception
of counter-intuitivess. The universe is "unimaginable" that is why it
is "counter intuitive". In fact "counter intuition" is just attempting
to imagine the unimaginable (at least in the case of relativity).
That's why I HATE those descriptions of relativity that say something
like "One observer would see the car contract in the direction of
motion" while the other would not. That is totally wrong. What each
observer would do is see the same thing as any other colocated
observer in the any other frame right next to him requardless of
relative velocity. Then they would CALCULATE a picture that they would
call "real". The results of the calculations differ but NOT the
observations on which they are base. I think a lot of the descriptions
of relativity are perversly causing a mysteriousness to the theory
because of that.
On Jan 29, 5:56 pm, "tg" <tgdenn...@earthlink.net> wrote:
> On Jan 29, 10:53 am, "Justintruth" <truth.jus...@gmail.com> wrote:
>
> > I agree. I got an "A" in electricity an magnetism in college. I could
> > do the equations trough rote memory but I just could not understand
> > why they called it "curl" or "divergence". I really wished they had
> > just drawn a picture on a blackboard.You took an E and M course and there were no pictures in the
Leon2
> Anyone here know what energy is?
>
> I don't want to see E=mc^2 because that just defines a process.
>
> We see the rocks and grass. We know what light is. Electric fields,
> Magnetic fields, are apparent by their presence and measured by Flux
> and Density etc.
>
> What is energy? Yeah we know that when electrons loose an orbital they
> emit energy...what is that?
>
> At least matter has some kind of mass and velocity or acceleration. Is
> it heat? What is heat?
>
> X
>
There doesn't have to be matter for motion. I've got a
thought-experiment for that:
Think of a circulair motion in front of you. When the motion is towards
you it could touch you. This means it's touchable, it's matter.
When the motion is away from you it pulls you like a wind, it's a force.
So motion divides in to phenomena: matter and force.
It now is silly to think of motion as needing matter. Matter is an
effect of motion. So is force (gravitational force).
Elementairy is the circular motion. You've got circular motions and
straight forward motions. If you study motions of waves on a circle you
get for exactly one wave on a circle a point of escape from the circle
for the wave. The escape of the wave is in packages, one wave on the
circle, one wave in straight forward motion. Light can be seen as single
short waves with a time interval travelling in a straight forward way.
Light seen as such will have the character of parts and of waves.
The waves still don't consist of something material. They can be seen as
breach in space and time. Mainly because there are so much circular
motions means that there exists something (it keeps repeating itself and
therefor "is")
Don't forget this is philosophical fantasy of course.
rc
whoa. :)
Leon2
Touching the + and - of an electrical cable gives a shock. Maybe it's
still linguering...