Re: Name that force

[sampere <sampere@PHYSICS.SYR.EDU>]

How do wheels roll on a friction free surface?  What force makes them roll?

Since the drops do not have any momentum in the forward direction, the
interaction of the drops with the walls of the open freight car are
ultimately responsible for accelerating the drops.  The walls exert a
force on the drops, the drops exert a reaction force back on the walls.
What do you call the force when you push on a wall?  Does it have a
special name?

Sam

Ludwik Kowalski wrote:

> In a conceptual question Hewitt asked what
> happens to the speed of an open freight car
> (increases, decreases or remains the same)
> when it rolls friction-free along a horizontal
> track while a pouring rain falls vertically.
>
> The expected answer is: "speed decreases
> as water accumulates in the car because the
> momentum must be conserved." What is a
> good name for a force responsible for the
> change in speed?
> Ludwik Kowalski