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Re: momentum

At 10:41 AM 7/2/99 -0500, Paul wrote:
Whoa! Did you really mean to say that the energy in Herb's example is
NOT conserved? The system's kinetic energy is obviously not conserved,
but I sure hope its energy is. Can we not agree that the word "energy"
without modifying adjective refers to total system energy?

I agree with Paul that the "system" and "energy" need to be carefully
defined, but if the collision includes a "wall" -- ie a lamp post, tree or
ditch, the system would have to be something impractical like the whole the
Universe for the total energy to be conserved.

I think that it is more helpful to calculate the energy change by the two
cars or by one of them -- which correlates with the damage done. And this
energy is NOT conserved.

But we keep talking about "momentum"! Why?

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen