Re: [Phys-l] momentum dissipation?

[chuck britton <cvbritton@mac.com>]

PLEASE don't ! ! ! !
Momentum should be SO much easier to understand than this.
My first real understanding of how momentum could be totally 
misconceived was in freshman physics class.
The problem was a classic - a railcar that has a load of coal dumped 
into it as it rolls down the track.
How much does it slow down? No big deal.
Then the cat coasts across a raised trestle and DUMPS it's load.
Does it speedup?!?!?!?!
No, the prof tells us - because the coal is still moving forward with 
its own momentum.
"oh" a student proclaims "I get it, the car doesn't speed up until 
the coal hits the ground!!!".
And somehow the US nuclear navy survived this NROTC kid's enlistment.

Pick your system.
Extend it enough to keep momentum constant or use N2 in it's delta p 
form to account for any gain/loss.

Momentum should be covered in it's entirety before acceleration comes 
up (except for a fancy word that means 'Slope of a Velocity Graph').

At 6:20 PM -0400 4/25/10, Bob Sciamanda wrote:
> Consider the case of a motorboat accelerating by exchanging momentum with
> the fluid water.  It would seem that in such cases it is legitimate to speak
> of the dissipation of  momentum by the water.  Similar cases occur with
> aircraft/atmosphere interactions.