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Re: Wave phase reversal on reflection



On Tue, 25 Apr 2000 23:04:50 -0400 Bob Sciamanda <trebor@VELOCITY.NET>
writes:
Herb,
How does the seat of your chair have "the brains or the muscles" to
push up on your fanny and keep you from falling?

The seat of my chair has no brains or muscles it just provides
a "thoughtless" reaction. No muscles are needed because the
chair does not require any mechanical energy (force times distance)
to keep my fanny stationary. When I first sit down on my chair
the wood compresses and, without thinking, it exerts an upward force
in a kinda knee-jerk patella-reflex reaction. (-:

Herb Gottlieb from New York City
(Where our chair seats that fail to react are subject to catastrophic
break-downs)

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
www.velocity.net/~trebor
----- Original Message -----
From: "Herbert H Gottlieb" <herbgottlieb@JUNO.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, April 25, 2000 10:55 PM
Subject: Re: Wave phase reversal on reflection


On Tue, 25 Apr 2000 22:16:12 -0400 Bob Sciamanda
<trebor@VELOCITY.NET>
writes:
Yes, but what is the physical mechanism whereby the cancelling,
reflected wave is generated? Perhaps something like: When an
upward
going vertical pulse on a rope encounters a rigid wall
termination, the
last rope segment exerts an
upward force on the wall. The wall responds by exerting a
downward
pull on
the rope segment (by N3), thus starting a downward going
vertical pulse

on the rope.

Bob....

An excellent try ! I really like it!!

The only trouble with the explanation above is that students
"know"
that a stupid wall does not have the brains or the muscles to
exert
a downward pull ....(unless the wall starts to collapse and fall
down
while
the string is attached). Perhaps it might be better to say that
the
rigid wall termination provides a reaction that has the "same
effect
as a person supplying a downward force on the rope". ......
but I'm sure that someone can provide a much better wording that
I can at the spur of the moment.

Herb
on the