Re: Name that force

[Larry Cartwright <exit60@CABLESPEED.COM>]

John Denker's exposition is IMHO a showpiece of clarity, of logical
progression.  What fun it is to see such excellent teaching.

I'm wondering if anyone on the list has a problem with the concept of a
"flow" of momentum?  We all know that treating quantities as if they
were substances has raised mighty objections from some Physl-L members
in the past.

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright                    Retired Physics Teacher
<exit60@cablespeed.com>              Charlotte MI 48813 USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

John Denker wrote:
> Consider the following situation:
>   -- Hopper-shaped car, so no rain can hit the front wall,
>      because of the sloping front wall.
>   -- Almost full of water, so no rain can hit the rear wall.
>
> .     \WWWWwwwwwwww/
> .      \          /
> .       \________/
> .  rear  OO    OO  front ==>
>
> In addition, somewhere hidden down in the undercarriage,
> there is a half-full bottle of water.  Spring water, not
> rainwater.
>
> Here's the momentum balance:
>
>    new rainwater slows down old rainwater
>    rainwater slows down car
>    car slows down bottled springwater.
>
> That is, the momentum flow is:
>    new rainwater
>      --> old rainwater
>           --> car
>                --> bottled springwater