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# Re: [Phys-L] Figuring Physics solution Jan 2018

If I apply a force to an object with an electric solenoid actuator, switching it off removes the force that it applies, does it not? I stop that force with a switch.
If I apply a force with a screw-jack, then that force is not controllable or 'stoppable' but may instead be permanent in this context.

Brian W

On 1/23/2018 4:30 PM, Todd Pedlar wrote:
You've illustrated perfectly by such a concept as an "unstoppable force" is
meaningless. :)

On Tue, Jan 23, 2018 at 4:26 PM, brian whatcott <betwys1@sbcglobal.net>
wrote:

It seems that there is a presumption that a permanent [cannot be stopped']
force necessarily causes movement. It does not.

On the other hand, a force which may be switched on or off may cause
motion. Or not!

Brian W

On 1/23/2018 1:44 PM, Todd Pedlar wrote:

That's the problem with a lot of the language of such questions - the
phrase "that cannot be stopped" is meaningless. I just don't know what
those words add to the context of any particular problem.

On Tue, Jan 23, 2018 at 1:42 PM, Philip Keller <
pkeller@holmdelschools.org>
wrote:

What is a force that "cannot be stopped"? I have no idea what that phrase
means in this context. Can anyone give me a definition and maybe an
example of a force that cannot be stopped and another example of a force
that can in fact "be stopped"?

On Tue, Jan 23, 2018 at 2:27 PM, Folkerts, Timothy J <
FolkertsT@bartonccc.edu> wrote:

Concrete example: a 10 newton force which cannot be stopped, bears
directly on a 1000 kg marble block anchored in the substrate rock. The
block cannot be moved.

What happens?

The 10^3 kg block anchored to the 6x10^24 kg earth accelerates at
1.7x10^-24 m/s^2.