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Re: Name that force



Ludwik wrote:-----Original Message-----

From: Ludwik Kowalski [mailto:kowalskil@MAIL.MONTCLAIR.EDU]
Sent: Tuesday, October 28, 2003 1:41 PM
To: PHYS-L@lists.nau.edu
Subject: Re: Name that force

The situation
can be further idealized. A cloud producing rain
is replaced be a shower-head staying above the
car. In that way the BACK wall and the FRONT
wall are dry. Will the car still be slowing down at
a rate proportional to the rate at which the mass
is increasing? I do not think so.

Two observations:

1. The back wall cannot stay dry, unless you drop the water into a barrel, in which case the back wall of the barrel exerts most of the horizontal force to accelerate the water.

2. The instantaneous force must be F = dp/dt = m dv/dt + dm/dt v ... it's clearly more complex than a ~ dm/dt

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George Spagna
Department of Physics
Randolph-Macon College
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e-mail: gspagna@rmc.edu
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