Re: A few silly questions

"David L. Burkhead" <dburkhead@xxxxxxx> wrote in message
news:e9ydnXCDop5mBE_YnZ2dnUVZ_sGqnZ2d@xxxxxxxxxxxxxxx
Ben Newsam wrote:
On Fri, 09 Feb 2007 19:56:24 GMT, "Wayne Dobson"
<nospam@xxxxxxxxxxxxx> wrote:

By the way, I'm not just asking these questions
because I'm too lazy to do any study, but that without any outside
input, I get the feeling that the person I'm arguing with feels at
liberty to call anything I say, wrong, regardless of its merits.

We get a few of those in here.

Unfortunately, Mr. Dobson is one of them. He only came here looking for
"ammo."

How come I didn't fire it, then?

I'm the person he was arguing with. The context was from his claim that,
in
the case of a falling body brought to a stop by a cord (as in a hanging),
"considering only those two factors [height and weight], the forces
involved
are very predictable." I immediately pointed out that those two factors
don't define the problem, let alone lead to "very predictable" forces.
Given only those two factors, the only thing that can really be said is 0
<
F < infinity. And since F here is magnitude rather than vector force,
that's really no restriction at all.

When we went around on this, the infinite force limit was brought up and
Mr.
Dobson said that of course that would require infinite energy (or words to
that effect). Which I disputed since, yes, you would have infinite force,
but, since (by the initial stipulation of the condition), it would take
place over zero distance. infinity * zero, undefined but possibly
meaningful if considered as a limit.

You said it was something which occured, which I disputed and you
maintained. The conditions set out under the limit that you are speaking of
do not occur, except as a concept. The argument was about reality, yet you
flit back and forth between theoretical concepts and reality - without
warning, so as to cause confusion.

(In this case, the limit should come to
simply the kinetic energy of the falling body--not the "infinite energy"
Mr.
Dobson claimed.) This, of course, leaves aside that stopping a moving
body
in a particular frame doesn't require energy.

If you were to stop the moving body, would it require energy?

Rather it gives up energy

Does it also give up force?

whether it's used to move something else or is given up as heat, breaking
things, whatever.

I guess you could stop a truck without using any energy or breaking a sweat,
then?

Several times over the course of the discussion I pointed out that the
infinite force--where the time over which it is applied and, by extention,
the distance over which it is applied, is zero--was the case "at the
limit."
Likewise the F=0 end (where the distance over which it is applied would be
zero. These were only cited as the extreme cases, the limits, which
illustrate why the claim of "forces are very predictable" is incorrect.

And, at the limit (speaking purely mathematically) there is no prohibition
on having a change in velocity/momentum occur in zero time. All you've
done
is specify a point in the position/time curve where the curve is
continuous
but at which the first and all subsequent derivatives does not exist.

How does something change in zero time? A plain English answer will
suffice.

Well, eventually, he finally got around to claiming that he actually meant
to include those other factors necessary to define the problem and we
should
just try to forget that he spent considerable time trying to defend the
original proposition, as originally worded.

It took me that long to figure out that you were being so pedantic.

--
AKA "Dobbie The House Elf"


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