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pmb
#10
Oct25-03, 12:27 PM
P: n/a
Originally posted by jcsd
I haven't looked over all of them, but they do seem okay to me, I've the feeling he might of lifted them from a textbook.
Some but not all.

For instance: The author keeps trying to define force as mass times acceleration. That has always gotten him into trouble in the past and I'm sure it will in the future too. In this particular case he tried to derive an expression for the Coriolis force. So he derived an expression for the Coriolis acceleration and then multiplied it times rest mass and calls that the "Coriolis force." His result is incorrect for that reason. His bogus derivation of the Coriolis force is here

http://www.geocities.com/zcphysicsms/chap6.htm#BM80

For a correct derivation see

http://arcturus.mit.edu/8.962/notes/gr6.pdf

Force is defined as the time rate of change of momentum - not as mass times acceleration. Bertschinger gets it right. The author of that web site you referanced was shown this and all he could do was his usual backpeddling - It was too silly of response to repeat here. For those interested go to sci.physics.relativity and read the thread "Centrifugal etc fict-force relativistic derivation"

Then there is the subject regarding tidal forces. He botches that up pretty bad. He does something bizzare - he defines tidal force differently than the rest of the world and then proceeds to show that there is no such thing as a gravitational tidal force. He tries to define tidal force in terms of 4-forces which is quite unlike the term is defined in General Relativity. His definition is that the tidal force is the gradient of a 4-force of a particle in free-fall which is total nonsense since the gravitational force is an inertial force and not a 4-force. Any decent GRist knows that as fact.

Then there is the time where he was totally unable to comphrend what a tidal force tensor was or how it is related to the Riemann tensor.

See - http://www.geocities.com/physics_wor...rce_tensor.htm

for the Newtonian definition. The GR definition is that the tidal force tensor is the Riemann tensor. They're related.

Then there is the part where he claims that by "curvature" cosmologists mean "Gaussian curvature" which is bogus as well.

Then there is his claim that a uniform gravitational field has spacetime curvature when its really defined as having no tidal forces.

Pete