let me first say that I have never read a better analysis on
pseudo-forces than the one David Bowman provided! However, I'd
like to respond to David's fourth point:
"4) It is at least cumbersome and probably problematic to consider
N3 as applying to forces exerted by disembodied force fields"
Here is passage relevant to the above point; the following is a summary of David Hestenes' text (see the original text for
more details):
"Hestenes (1998, 11) defines the third law:
'To the force exerted by any object on a particle there
corresponds an equal and opposite force exerted by the particle
on that object.'
The relation [f12 = - f21, both vectors] is satisfied by Newton’s gravitational force law and Coulomb’s law, but it fails for
direct magnetic interactions between charged particles.
Newton's third law can be rewritten in terms of the rate at
which momemtum changes (for a two-particle system):
dp1/dt = -f21 (p and F as vectors)
This equation can be interpreted as a law of momentum exchange. Hence, a failure of the third law would be a failure of the law
of conservation of momentum. The law of conservation of momentum
is regarded as more fundamental than Newton’s laws because it
holds in modern physics as well. Classical field theory can be
used to explain magnetic interactions between charged particles
by attributing momentum to the electromagnetic field. This saves
the third law in magnetic interactions between charged particles
if the ‘object’ in the third law is interpreted as a field."
It seems that there are people in physics (probably more than Hestenes :-)) who are ready to accept field as an 'object' in the above sense.
Regards,
Antti
Antti Savinainen
Kuopio Lyseo High School
Finland
E-mail: <antti.savinainen@kuopio.fi>
Website: <http://kotisivu.mtv3.fi/physics/>
Reference:
Hestenes, D. (1998). Foundations of mechanics (Originally published as Chapter 9 in the first edition of New Foundations for Classical Mechanics, 1986). Online at <http://modelingnts.la.asu.edu/pdf/Foundations.pdf>
--
Viesti on tarkastettu MailScanner ohjelmistolla
virusten ja roskapostien suodattamiseksi.
Kuopion kaupunki / ATK-keskus
--