Re: My definition of force!!!
From: PD (pdraper_at_yahoo.com)
Date: 03/08/05
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Date: 8 Mar 2005 08:36:28 -0800
TomGee wrote:
> PD wrote:
> > TomGee wrote:
> > > PD wrote:
> > > > TomGee wrote:
> > > > > PD wrote:
> >
> > [snip]
> > > >
> > > It is not only me, but most scientists agree with me, as shown
> below.
> > >
> > > "Usually, several forces act on an object at once. If multiple
> forces
> > > combine to give a net force that is zero, then the object will
not
> > > accelerate; the object will either remain motionless or continue
> > moving
> > > at a constant velocity. For example, if a person pushes a
shopping
> > cart
> > > with a force equal in magnitude to the force of friction that
> opposes
> > > the cart's motion, the forces will cancel, giving a net force of
> > zero.
> > > As a result, the cart will move down the aisle with a constant
> > > velocity. If the person suddenly stops pushing the cart, the only
> > force
> > > acting on the cart is the frictional force. Since the net force
is
> no
> > > longer zero, the cart accelerates: its velocity drops to zero."
> > > Microsoft ® Encarta ® Reference Library 2005. © 1993-2004
> > Microsoft
> > > Corporation. All rights reserved.
> > > Note that the net force is non-zero whenever any force is acting
on
> > the
> > > cart, and so that means that zero energy expended means zero
force.
> >
> > I see. So apparently you are having difficulty reading and
> > understanding even Microsoft Encarta blurbs. No where in there does
> it
> > say that the net force is nonzero whenever any force is acting on
the
> > cart.
>
>
> No, but it states that forces can combine to provide a zero net
force,
> which means that a zero net force does not necessarily indicate a
total
> lack of forces involved. Two forces can combine to produce planetary
> and satellite orbits like the Earth's gravitational force pulls on
the
> moon but the centrifugal force pulls it away and prevents it from
> crashing into us. It's a standoff where the net force is zero not
> because there are no forces acting on the moon but because the two
> forces even out to produce a zero net force.
I was so *hoping* you would say that. In this particular case, the net
force is NOT zero, and yet there is no energy expended. Note the
following facts:
1. There is no such thing as centrifugal force. There is no agent that
could push the satellite outward. If you think there is, name the agent
of the force that is doing the outward pushing. (Centrifugal force is a
common misconception, a "pseudoforce" in physics.)
2. You yourself said that if gravity were turned off (and ONLY gravity
-- no changes to any other forces that may or may not be present), the
satellite would separate from the Earth, because it would proceed in a
straight line, constant velocity motion tangentially away from the
Earth. Straight line, constant velocity motion is evidence for *no* net
force being present. Where has this so-called centrifugal force gone?
Recall we only took away gravity.
3. In any circular motion, like the motion of a satellite, there is
acceleration. This acceleration is called centripetal acceleration, it
is toward the center of the circle, and it has magnitude v^2/r. Note
that this acceleration is a change in *velocity* without implying a
change in speed.
4. The presence of a net acceleration implies the presence of a net
force. Because of Newton's 2nd law, F_net = m*a, the net force F_net
must point in the same direction as the acceleration.
5. In circular motion, like the motion of a satellite, there is indeed
a net force inward. (In the case of the satellite, that force is
clearly the force of gravity toward the Earth.) Indeed, if it were in
equilibrium, the satellite would travel in a straight line at constant
speed, by Newton's 1st law.
6. Despite there being a net force (indeed, a single force) acting on
the satellite, there is no energy expended. It does not change speed
and therefore it's kinetic energy remains the same. Its gravitational
potential energy doesn't change, because it neither approaches nor
recedes from the Earth's surface through an orbit, it doesn't heat up
or cool down. Where is the energy expended by this net force going????
> >
> >
> > In fact it says:
> > "If multiple forces combine to give a net force that is zero..."
> > Namely, here is a case where there are nonzero forces present and
> they
> > combine to give a zero net force.
> >
> >
> Yes, thank you. That is exactly what I said and what you stubbornly
> deny.
What you said was the following:
> Note that the net force is non-zero whenever any force is acting on
the
> cart, and so that means that zero energy expended means zero force.
This statement is in direct conflict with what you just said.
>You insist that when there is a net zero force it means there
> are no nonzero forces involved.
On the contrary, this is what YOU said. I, on the other hand, pointed
out a couple cases where there is a net zero force and nonzero forces
involved.
> It seems that you are the one having
> problems understanding even common language blurbs written for the
> unprofessional physicist,
I *love* that phrase, "unprofessional physicist". It's so much more apt
than "amateur physicist".
> even while you claim to be a professional
> one.
On the contrary, anyone reading this thread will see that you are the
one that misinterpreted the Encarta blurb, and you are now trying to
attribute that misinterpretation to me.
> >
> >
> > Notice too in the next sentence:
> > "For example, if a person pushes a shopping cart with a force equal
> in
> > magnitude to the force of friction that opposes the cart's motion,
> the
> > forces will cancel..." This does NOT mean that because the net
force
> is
> > zero, then the person's push must be zero or that the friction must
> be
> > zero. Quite the contrary, anyone that has pushed a shopping cart
> > recently knows that both forces are definitely NONzero. And yet
there
> > is no change of energy of the cart!
> >
> >
> Yes, that is precisely my point and exactly what you have denied up
to
> now.
What you said was:
> Note that the net force is non-zero whenever any force is acting on
the
> cart, and so that means that zero energy expended means zero force.
It seems you were the one denying it, not me.
> You forget your role as the Devil's Advocate and attempt to
> assume my role of the hero!
You view yourself as a hero, a martyr to science, do you?
> Where does that leave the other posters
> who Lemmingly followed you off the cliff, PD?
>
> Now that you agree that there can be forces acting on objects such
that
> they combine to produce a zero net force, you lose your argument that
> the banner and the cup have no forces acting upon them because they
are
> not being displaced.
Again, you misquote me. The sign and the cup DO have forces on them. To
remind you what I said, the cup has two forces acting on it: the force
of gravity and the contact force of the table. The sign has two forces
acting on it: the force of gravity and the tension in the cable. None
of the forces mention expend any energy however, and the energy of the
sign and the energy of the cup are unchanged, exactly as the cart in
the Encarta example.
I'm glad you're learning something. Here are cases where there are
clearly forces present, but no energy expended. So force cannot be "the
expression of energy" or identified with energy-in-use, do you not
agree?
> >
> > What is NOT captured in the Encarta blurb (because its editorially
> > required brevity demands that a full explanation must be
sacrificed)
> > are OTHER circumstances in which a force does not lead to energy
> > expended: a) cases where there is no displacement whatsoever, b)
> cases
> > where the displacement is perpendicular to the direction of the
> force.
> >
> >
> Oh Lordy Lordy, the human race is doomed!!
And yet you just agreed with me for circumstance (a), did you not? See
above!
Now all we have to do is address circumstance (b), don't we?
See the satellite case above.
> >
> >
> > > The net force left on the cart is the frictional force which is
> > caused
> > > by the gravitational force pulling the wheels to the ground.
> > > > > >
> > > > > >
> > > > > > Look up the work-energy theorem.
> > > > > >
> > > > > > If the force of gravity is acting on an object, but there
is
> NO
> > > > > > displacement in the direction of the force of gravity, then
> > there
> > > > > will
> > > > > > be NO energy expended by that force.
> > > > > >
> > > >
> > > I show above where that is patently false.
> >
> > You realize, of course, that you are denying Newtonian physics?
Look
> up
> > the work-energy theorem. You may need something a bit more
> > comprehensive than Encarta.
> >
> >
> No, it is you who denies classical physics. Post your arguments
based
> on your theorem if you wish, but simply throwing theorems at the
> problem is the same as throwing websites at it, i.e., that is only
for
> dolts too dense to be able make specific arguments in support of
their
> disagreements. If you believe that your theorem really does
overthrow
> my claim, why not post it here for us all to decide if it does or
not.
> You won't do that because, obviously, it cannot deny my claims.
First of all, it's not my theorem. Secondly, it is a theorem that is
carefully explained in EVERY introductory physics text, including high
school texts. I'm not about to be browbeaten into typing a long passage
here to save you the work of going to the library and reading a
chapter. It's not the role of this forum to provide people a complete
reference for learning physics. Heck, why don't you use Wikipedia?
(Hint: search for "mechanical work").
[snip]
> > > >
> > > >
> > > > > I have already disposed of your coffee cup and cable
examples,
> so
> > I
> > > > > will deal with your orbiting moon philosophy.
> > > >
> > > > You have not disposed of the coffee cup and cable examples.
Both
> > are
> > > > cases where there is a force present and no energy expended. In
> the
> > > > sign-on-a-cable example, you actually declare that the sign
> should
> > > heat
> > > > up due to the energy expended by gravity -- which is something
> that
> > > is
> > > > easily experimentally testable, and in fact common experience
> (that
> > > is,
> > > > everyday experiments) rule out.
> > > >
> > > >
> > > No, I have said no such thing.
> >
> > You deny saying the following?
> > ============
> > > > > > > > > A sign suspended from a beam by cable is under the
> > influence
> > > > > > > > > of the force of gravity on Earth.
> >
> >
> No. I said that, but that is not what you said I said.
> >
> >
> > > > > > > > > PD: But it is not moving. There is no expenditure of
> > > > > > > > > energy! If so, what is it?
> > > > > > >TomGee: The force of gravity is pulling on it
continuously.
You said the above line, too.
> > > > > > PD: I see. And where does that energy go? Does it heat up
the
> > > > > > sign?
> > > > > TomGee: It is conserved, that's where it goes.
And you said the above line, too.
> > > > PD: Wow! You really believe that, and it doesn't bother you?
The
> > > > longer the sign just hangs there, the warmer it gets?
> > > Tom Gee: If the sun is shining on it....
> > ===========
> >
> Look above, it turns out it was you who said what you claim I said.
Uh, no. You were the one that said that the energy heats up the sign.
Do you really have the balls to deny that you said it?
> > > >
> > > > >
> > > > > Were you not taught in hs that the moon is caught in the pull
> of
> > > the
> > > > > Earth's gravitational field and that is what keeps it in
orbit,
> > but
> > > > if
> > > > > suddenly there were no attractive force then the moon would
> just
> > > keep
> > > > > on going into space away from Earth?
> > > >
> > > > I did not say that the force was zero. I said that the force
was
> > > > present but the energy expended was zero, because there is no
> > > > displacement in the direction of the force. It is only you who
is
> > > > wedded to the mistaken idea that if the energy expended is
zero,
> > the
> > > > force must be zero.
> > > >
> > > >
> > > Again, see above where I point out your error.
> >
> > No error pointed out. How does the Encarta blurb point out an error
> in
> > my statement?
> >
> >
> By showing that a net zero force can be created by forces expending
> energy to the effect that they cancel each other out.
Forces canceling does not imply that they are expending energy in so
doing. Where is the energy from the forces applied to the cup going?
Where is the energy from the forces on the sign going?
And in the case of the satellite, there is a NONzero net force, and yet
there is no energy expended!
> >
> >
> > [snip]
> > > >
> > > >
> > > > > My model is just a series of alternative explanations of
> observed
> > > > > phenomena which begins with time and progresses through the
> > > creation
> > > > of
> > > > > light. It resolves some current explanations of issues which
> > have
> > > > led
> > > > > us all into dead-end alleyways from which we cannot get out.
> > > >
> > > > Name one dead-end.
> > > > Name your theory's explanation that is successful where the
> current
> > > > model has no consistent explanation.
> >
> > Lack of response noted.
Further lack of response noted.
> >
> > > >
> > > > > Plus it
> > > > > provides fresh looks at the issues and a chance for readers
to
> > get
> > > > > ideas on their own and perhaps come up with even better ideas
> > than
> > > > > mine.
> > > >
> > > > Ideas are worthless until they have shown some bearing on
reality
> > --
> > > > that is, that they extend our predictive powers.
> > > >
> > > > > >
> > > No, not so. New ideas can be worth their weight in platinum,
else
> > > corporations would not spend resources to hold brain-storming
> > sessions
> > > where participants are encouraged to submit anything that comes
> into
> > > their minds during the sessions, no matter how imaginative they
may
> > be.
> >
> > You know why they do that? Because the people that they invite to
> those
> > sessions that have demonstrated to have ideas that are 1)
productive,
> > 2) based on reality and previous lessons learned, 3) and are still
> > imaginative. All three are required. Those that produce ideas that
> > satisfy only one of these criteria are not invited back to those
> > sessions.
> >
> No, there are no such limitations for participation; you just made
all
> that up.
I see. And how many of these corporate brainstorming sessions have you
been invited to? And on what topics?
I know it must seem like I'm telling you there's no Easter bunny, but
I'm not making it up.
You see, I have the advantage of both corporate and academic career
experience.
Much as it would be nice to tell you that there is a reward for people
who simply want to THINK, without accountability for the reality of
their notions, it ain't so, Tom. Grow up.
> >
> > You have such a naive and misguided view of the market value of
free
> > and unconstrained imagination, Tom.
> >
> Certainly you have the right to your own opinions, PD.
And experience, Tom.
> >
> >
> > > Ideas are all that Theoretical Physics holds dear since they
> disdain
> > > experimental research. So, again, you are wrong.
> >
> > Disdain?! Where the HELL did you get that impression? To which
> > theorists have you asked this question and who remarked that they
> > disdain experimental research? Please be specific, because I've
> worked
> > as an experimentalist side-by-side with theorists, applying our
> > different skill sets to the same problems. I can tell you from
> personal
> > experience, Tom, that you are plainly talking out of your rear end
on
> > this one. In fact, I know several theorists that would be deeply
> > offended by this comment.
> >
> > > > > >
> I did that once already for you, but here it is again:
>
> Theoretical Physics, physics employing mathematical models and
> abstractions rather than experimental processes.
And where do you see "disdain" in that? Where do you see "without
regard for experimental verification"? Where do you see "without
collaboration with experimentalists"? Where do you see "without need
for discriminating quantitative predictions"?
Basing your understanding of theoretical physics on a twelve-word
definition is like claiming you understand art on the basis of a box of
twelve crayons.
>
> For information on:
>
> · theoretical physicists, see Aage Niels Bohr; Niels Henrik Bohr;
Max
> Born; Louis Victor Broglie; Freeman Dyson; Albert Einstein; Enrico
> Fermi; George Gamow; Werner Heisenberg; Lev Landau; Gilbert Newton
> Lewis; J. Robert Oppenheimer; Blaise Pascal; Wolfgang Pauli; Max
> Planck; Georg Friedrich Riemann; Andrey Sakharov; Abdus Salam; Erwin
> Schrödinger
> · theoretical object that can absorb all radiation without
reflecting
> or emitting radiation itself, see Blackbody
> · important discoveries developed through theoretical physics, see
> Exclusion Principle; Planck's Constant; Atom: Line Spectra
> · prediction of antiparticles, Elementary Particles: Classification
> · use of mathematical field principles in theoretical physics, see
> Field (mathematics)
> · attempts in theoretical physics to unify three fundamental forces
> of nature into a single theory, see Grand Unification Theories
> · research facility for the study of theoretical physics and other
> advanced disciplines, see Institute for Advanced Study
>
>
> Microsoft ® Encarta ® Reference Library 2005. © 1993-2004
Microsoft
> Corporation. All rights reserved.
>
> > > > > >
> > > SNIP
> > > >
> > > > > Um, what empirical evidence is that?
> > > >
> > > > Precession of the perihelion of Mercury, synchrotron design and
> > > > operation, GPS satellite corrections required by SR and GR and
> not
> > > > predicted by classical physics, predictions of black holes and
> the
> > > > evidence by which we would see evidence of them, curvature of
> light
> > > in
> > > > a gravitational field and gravitational lensing of distant
> > galaxies,
> > > > the expansion of the universe.... Shall I go on? There's a
rather
> > > long
> > > > list.
> > > >
> > > > > >
> > > No. I asked for the one you claim overthrows classical physics,
> which
> > > is the one you failed to list.
> >
> > All of those listed. Classical physics has predictions about
> precession
> > of perihelion of Mercury, and it's wrong. Classical physics has
> > predictions about synchrotron design, and it's wrong (which was
> > discovered in early cyclotrons before it was too late, thank
> goodness).
> > Classical physics has predictions about the clock behavior on GPS
> > satellites, and it's wrong, and the SR and GR-guided corrections to
> > classical algorithms are now built into GPS satellites. Classical
> > physics not only does not predict black holes but predicts that
they
> > should not exist, and it's wrong. Classical physics does not
predict
> > gravitational lensing, and in fact says it should not happen, and
> it's
> > wrong. Shall I go on?
Lack of response noted.
> >
> > > >
> > > > > >
> > > > Has it ever crossed your mind that "honest research,
theoretical
> or
> > > > empirical" and "consistent with the way I view our world" are
> > > mutually
> > > > incompatible?
> > > >
> > > > > >
> > > Yes, of course.
> >
> > I believe you should investigate that possibility more strongly.
> >
> How will that help you to understand physics better?
It will help YOU understand how to do science better.
> > > > > >
> > > > > >
> > > SNIP
> > > > >
> > > > > ...I have never
> > > > heard
> > > > > of a real physicist ever arguing that an encyclopedia was
> wrong,
> > > >
> > > >
> > > > I don't think you've ever asked the question directly.
> > > >
> > > >
> > > Wrong again. You're running out of bullets.
> >
> > Whom have you asked? Be specific. And I've just started, not even
> > reloaded once yet.
> >
> > > >
> Attempt at distraction noted.
Bull. You claimed you asked the question directly. I'm challenging that
claim. Back it up.
> > > >
> >
> > > > Why don't you
> > > > post a link to an Encarta definition, or quote it directly, and
> ask
> > > the
> > > > physicists here think it is correct? Note there is a similar
> > approach
> > > > by someone named Paulps in these newsgroups who is receiving
> > exactly
> > > > that criticism from the physicists in the group.
> > > >
> > > >
> > > I have done that very same thing.
> >
> > Reference please.
> >
> > > >
> Everything posted here is a cry for critical review from those who
> should know better. If some like you respond, that's helpful, but
few
> well-known authorities in the field respond here. Mostly it's the
> regulars who respond with their own studied beliefs.
So you are now saying that you have NOT asked a physicist directly
whether an Encarta blurb is accurate or complete.
>
> I have been posting excerpts from my essay here since 1996 and if any
> physicists replied, most if not all never claim to be such. You're
an
> exception, of course.
OK, so then I am your FIRST case of a declared physicist that has
challenged the accuracy and completeness of an Encarta blurb? Do you
then value my opinion?
> >
> > > >
> > > > > but
> > > > > plenty of them argue about many authors works and their
ideas.
> > > Your
> > > > > argument on this subject has failed each time you have tried
> it.
> > > You
> > > > > should abandon it.
> > > >
> > > > How has my argument failed? What constitutes success to you?
> > > >
> > > > >
> > > Your argument that encyclopedias are less worthy references than
> > those
> > > in FAQs and physics books failed because the facts in Encarta and
> > > Wikkipedia are supported by authorities in the field, even if not
> by
> > > you.
> >
> > Which authorities? Cited authors and reviewers for Encarta,
please...
> > (I note that you have not once posted a Wikkipedia reference in
this
> > discussion, so your reference to Wikkipedia is irrelevant.)
> >
> >
> So can I take that to mean you believe in Wikkipedia but not in
> Encarta?
I didn't say that at all. I simply noted that your claim that Wikipedia
is supported by authorities in the field is irrelevant, because you
haven't cited Wikipedia.
> Is physics in your mind a popularity contest? I asked you
> before to stop making arguments that pit some reference works against
> others.
I can't do that. There are unquestionably some references that are
better, more complete, and more accurate than others. It is not a
matter of popularity. It is a matter of the intent of the publication.
Encarta is not intended to be a physics reference, and as a result, it
does not successfully serve as one.
> I explained how bankrupt such arguments are based on how
> information is gathered for sale to the public.
And you have no idea how publishing works, my friend. And I would be
REALLY careful about claiming that I don't, either.
> >
> >
> > And what about my arguments about your faulty reading and
> understanding
> > of Encarta blurbs? How have my arguments there failed? What
> constitutes
> > success to you?
> >
> >
> Well, I show above how it is you who suffers from that, not me.
See the above and deny it again.
PD
>
> TomGee
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