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Re: momentum conservation(2)



Hi John,
The crux is not a difference in time; both forces operate for the same
time duration. But during that common "force-operating time interval"
each particle may travel a different distance through space (than the
other particle).

It may help to note that (eg., in one dimension):
ma*dx =mv*dv, the integral of which is the change in mv^2 [a scalar]
(regardless of the details of the motion).
Compare with ma*dt=m*dv, whose integral is the change in mv [a vector].
The mathematics and the physics allow the change in the system "mv"
[vector] to be zero, even though the change in the system mv^2 [scalar]
may be non-zero.

Bob

Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: "John Barrer" <forcejb@YAHOO.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, March 14, 2000 10:45 AM
Subject: momentum conservation(2)


. . . During the Pasco cart collision, momentum is
transferred during the entire time of contact (during
which forces act) but the motions of the CMs of the
cars (ie, the velocities) are only changed during a
portion of the contact time. That is, the integral of
Fdx occurs over a different (ie, shorter) time than
that during which there is momentum transfer. During
the "rest" of the time energy is "dissipated"
internally producing an increased internal energy
which does not contribute to CM motion.
. . .