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Droping a Slinky (Q&A)

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Eric Charles

Droping a Slinky (Q&A)

Below are links to some science videos nifty for two reasons.

1) They ask and answers a pretty cool question: What happens when you hold a slinky out at shoulder height, so it is extended down (the bottom still off the ground) and you let go. Think about it for a second. How does the top part of the slinky move, how does the bottom part move, how does the center of mass move? A good physics thought experiment! (If you are having trouble imagining it, here is the question: http://www.youtube.com/watch?v=wGIZKETKKdw)

2) The answer illustrates the weirdness of trying to apply the term 'information' to all possible situations. At about 1:30, the physics prof offers an explanation for what happens, and (for just a second) talks as if one part of the slinky is transmitting 'information' about its movement to another part of the slinky, which is bizarre way. The slinky itself is moving, it is not transmitting information about the movement, it IS moving. Why would you say that it takes time for 'the information to propagate', instead of simply saying that 'it takes time for the slinky to move'. Weird, weird, weird.

At any rate, Here is the cool answer: http://www.youtube.com/watch?v=eCMmmEEyOO0
(and it continues here: http://www.youtube.com/wa! tch?v=oKb2tCtpvNU&NR=1)

This seemed like the type of thing lots of people on the list would get a kick out of... so... hope you do.

Eric

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FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org

Tom Johnson

Re: Droping a Slinky (Q&A)

Good questions, and I have another one: What is it about Slinky that young children find so fascinating and fun?

-tj

On Sat, Oct 1, 2011 at 7:07 PM, ERIC P. CHARLES <[hidden email]> wrote:

Below are links to some science videos nifty for two reasons.

1) They ask and answers a pretty cool question: What happens when you hold a slinky out at shoulder height, so it is extended down (the bottom still off the ground) and you let go. Think about it for a second. How does the top part of the slinky move, how does the bottom part move, how does the center of mass move? A good physics thought experiment! (If you are having trouble imagining it, here is the question: http://www.youtube.com/watch?v=wGIZKETKKdw)

2) The answer illustrates the weirdness of trying to apply the term 'information' to all possible situations. At about 1:30, the physics prof offers an explanation for what happens, and (for just a second) talks as if one part of the slinky is transmitting 'information' about its movement to another part of the slinky, which is bizarre way. The slinky itself is moving, it is not transmitting information about the movement, it IS moving. Why would you say that it takes time for 'the information to propagate', instead of simply saying that 'it takes time for the slinky to move'. Weird, weird, weird.

At any rate, Here is the cool answer: http://www.youtube.com/watch?v=eCMmmEEyOO0
(and it continues here: http://www.youtube.com/wa! tch?v=oKb2tCtpvNU&NR=1)

This seemed like the type of thing lots of people on the list would get a kick out of... so... hope you do.

Eric

============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org

--
==========================================
J. T. Johnson
Institute for Analytic Journalism -- Santa Fe, NM USA
www.analyticjournalism.com
505.577.6482(c) 505.473.9646(h)
http://www.jtjohnson.com [hidden email]
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FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org

Bruce Sherwood

Re: Droping a Slinky (Q&A)

In reply to this post by Eric Charles

The "information" way of describing this is a powerful and appropriate
way to describe this phenomenon. Another word that comes in
(especially in the case of electromagnetic phenomena) is
"retardation": When you flip the light switch in a room, the electric
field in the bulb filament cannot change for an amount of time equal
to the distance from switch to filament divided by the speed of light
("retardation"), and then the field does change and starts moving
electrons in the bulb filament, and the bulb starts glowing.
Incidentally, the mobile electrons in the copper wires leading to the
bulb move with extremely slow drift speeds. On average, a mobile
electron near the light switch takes about 30 minutes to reach the
bulb. So it really is information (change of electric field) that is
transmitted rapidly, not the moving objects.

Until the ("sound" or "mechanical") wave in the slinky propagates down
to lower parts of the hanging slinky, there is no reason/cause for the
lower parts of the slinky to change position, and they don't. And as
long as the lower parts of the slinky are stretched, they will
continue to support the load below them just as they had been doing
before the top of the slinky was released. Hence the bottom of the
slinky will not move until the wave has propagated down far enough
that the slinky just above the bottom is no longer stretched.

Here's an article about the slinky phenomenon, in which the physicist
Rhett Allain, blogging for Wired, models the motion using VPython
(vpython.org):

http://www.wired.com/wiredscience/2011/09/modeling-a-falling-slinky/

Bruce

On Sat, Oct 1, 2011 at 7:07 PM, ERIC P. CHARLES <[hidden email]> wrote:

> Below are links to some science videos nifty for two reasons.
>
> 1) They ask and answers a pretty cool question: What happens when you hold a
> slinky out at shoulder height, so it is extended down (the bottom still off
> the ground) and you let go. Think about it for a second. How does the top
> part of the slinky move, how does the bottom part move, how does the center
> of mass move? A good physics thought experiment! (If you are having trouble
> imagining it, here is the question:
> http://www.youtube.com/watch?v=wGIZKETKKdw)
>
> 2) The answer illustrates the weirdness of trying to apply the term
> 'information' to all possible situations. At about 1:30, the physics prof
> offers an explanation for what happens, and (for just a second) talks as if
> one part of the slinky is transmitting 'information' about its movement to
> another part of the slinky, which is bizarre way. The slinky itself is
> moving, it is not transmitting information about the movement, it IS moving.
> Why would you say that it takes time for 'the information to propagate',
> instead of simply saying that 'it takes time for the slinky to move'. Weird,
> weird, weird.
>
> At any rate, Here is the cool answer:
> http://www.youtube.com/watch?v=eCMmmEEyOO0
> (and it continues here: http://www.youtube.com/wa! tch?v=oKb2tCtpvNU&NR=1)
>
> This seemed like the type of thing lots of people on the list would get a
> kick out of... so... hope you do.
>
> Eric
>
> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at cafe at St. John's College
> lectures, archives, unsubscribe, maps at http://www.friam.org
>

============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org

Eric Charles

Re: Droping a Slinky (Q&A)

In reply to this post by Eric Charles

Bruce says:
Until the ("sound" or "mechanical") wave in the slinky propagates down to lower parts of the hanging slinky, there is no reason/cause for the lower parts of the slinky to change position, and they don't. And as long as the lower parts of the slinky are stretched, they will continue to support the load below them just as they had been doing before the top of the slinky was released. Hence the bottom of the slinky will not move until the wave has propagated down far enough that the slinky just above the bottom is no longer stretched.

I says:
Yes, exactly!
Why would you want to take that perfectly good explanation and insert things like "The bottom part of the slinky doesn't know to move until it gets information indicating that the top part is falling." The idea that you enhance the physical description of the slinky by anthropomorphizing it in that way is weird. (Note, this clearly isn't a Shannon 'information' thing either... at least not as far as I can tell. I cannot see anything analogous to a decision being made after a clarification of uncertainty. There is no analog to signal and noise.)

Nick Thompson

Re: Droping a Slinky (Q&A)

Hi, Eric,

I agree that using the term signal to describe “anything that happens” or term “information” to describe “anything related to anything that happens” is bad form.

But who did that? Certainly not Bruce.

When you (eric) wrote

Why would you want to take that perfectly good explanation and insert things like "The bottom part of the slinky doesn't know to move until it gets information indicating that the top part is falling." The idea that you enhance the physical description of the slinky by anthropomorphizing it in that way is weird

Who were you quoting? I know people who talk like that. But the “you” was a “one-you” not a “you-you”, right?

And what about hero Gibson’s use of the term? Doesn’t he refer to “information pickup” as if the physical relation between two thing constitutes knowledge about the one provided by the other?

I haven’t looked at the videos yet.

Nick

From: [hidden email] [mailto:[hidden email]] On Behalf Of ERIC P. CHARLES
Sent: Saturday, October 01, 2011 9:44 PM
To: Bruce Sherwood
Cc: The Friday Morning Applied Complexity Coffee Group
Subject: Re: [FRIAM] Droping a Slinky (Q&A)

Bruce says:
Until the ("sound" or "mechanical") wave in the slinky propagates down to lower parts of the hanging slinky, there is no reason/cause for the lower parts of the slinky to change position, and they don't. And as long as the lower parts of the slinky are stretched, they will continue to support the load below them just as they had been doing before the top of the slinky was released. Hence the bottom of the slinky will not move until the wave has propagated down far enough that the slinky just above the bottom is no longer stretched.

I says:
Yes, exactly!
Why would you want to take that perfectly good explanation and insert things like "The bottom part of the slinky doesn't know to move until it gets information indicating that the top part is falling." The idea that you enhance the physical description of the slinky by anthropomorphizing it in that way is weird. (Note, this clearly isn't a Shannon 'information' thing either... at least not as far as I can tell. I cannot see anything analogous to a decision being made after a clarification of uncertainty. There is no analog to signal and noise.)

Eric Charles

Re: Droping a Slinky (Q&A)

In reply to this post by Eric Charles

Sorry for any confusion.

It was the videos that I thought people might like... and then any discussion it generated might be bonus. Maybe I shouldn't have said anything, and just forwarded the videos.

The demonstrator in the video has been teaching physics at the University of Sydney for quite a long time. He uses information-speak in a few places. One example is when he explains that the bottom does not move:

"until the bottom end gets the information that the tension has changed. It takes time for that information to propagate down through the slinky to reach the bottom end. It is propagating down as a compressional wave."

The host/narrator in the video then throws in the term 'know' a couple of times, and the demonstrator goes along with it smoothly.

In contrast, Bruce gave a perfectly good explanation without any of that additional baggage. So why do so many people (including professional physicists) find the 'information' and 'know' language so appealing?

Eric

P.S. I thanked Bruce off list for the very cool and insightful explanations regarding the speed of light, but I'll mention my thanks again here.

On Sun, Oct 2, 2011 12:58 AM, "Nicholas Thompson" <[hidden email]> wrote:

Hi, Eric,

I agree that using the term signal to describe “anything that happens” or term “information” to describe “anything related to anything that happens” is bad form.

But who did that? Certainly not Bruce.

When you (eric) wrote

Why would you want to take that perfectly good explanation and insert things like "The bottom part of the slinky doesn't know to move until it gets information indicating that the top part is falling." The idea that you enhance the physical description of the slinky by anthropomorphizing it in that way is weird

Who were you quoting? I know people who talk like that. But the “you” was a “one-you” not a “you-you”, right?

And what about hero Gibson’s use of the term? Doesn’t he refer to “information pickup” as if the physical relation between two thing constitutes knowledge about the one provided by the other?

I haven’t looked at the videos yet.

Nick

From: [hidden email] [mailto:[hidden email]] On Behalf Of ERIC P. CHARLES
Sent: Saturday, October 01, 2011 9:44 PM
To: Bruce Sherwood
Cc: The Friday Morning Applied Complexity Coffee Group
Subject: Re: [FRIAM] Droping a Slinky (Q&A)

Bruce says:
Until the ("sound" or "mechanical") wave in the slinky propagates down to lower parts of the hanging slinky, there is no reason/cause for the lower parts of the slinky to change position, and they don't. And as long as the lower parts of the slinky are stretched, they will continue to support the load below them just as they had been doing before the top of the slinky was released. Hence the bottom of the slinky will not move until the wave has propagated down far enough that the slinky just above the bottom is no longer stretched.

I says:
Yes, exactly!
Why would you want to take that perfectly good explanation and insert things like "The bottom part of the slinky doesn't know to move until it gets information indicating that the top part is falling." The idea that you enhance the physical description of the slinky by anthropomorphizing it in that way is weird. (Note, this clearly isn't a Shannon 'information' thing either... at least not as far as I can tell. I cannot see anything analogous to a decision being made after a clarification of uncertainty. There is no analog to signal and noise.)
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org

Eric Charles

Professional Student and
Assistant Professor of Psychology
Penn State University
Altoona, PA 16601

Stephen Guerin

Re: Droping a Slinky (Q&A)

In reply to this post by Eric Charles

Cool! Thanks, Eric.

I was curious and mocked up a quick spring model in Netlogo to play
with the dynamics. You can see a video here
http://www.youtube.com/watch?v=AtWiM5jicOI

-S

On Sat, Oct 1, 2011 at 7:07 PM, ERIC P. CHARLES <[hidden email]> wrote:

Nick Thompson

Re: Droping a Slinky (Q&A)

Stephen,

I take it that your model's "intuition" is that the bottom should start
moving a bit before the top gets to it.

I looked at Eric's video again and again, feeling that I had seen something
like it before. And then I remembered what that something was. The
collapse of the twin towers.

N

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Stephen Guerin
Sent: Sunday, October 02, 2011 1:04 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: Re: [FRIAM] Droping a Slinky (Q&A)

Cool! Thanks, Eric.

I was curious and mocked up a quick spring model in Netlogo to play with the
dynamics. You can see a video here
http://www.youtube.com/watch?v=AtWiM5jicOI

-S

On Sat, Oct 1, 2011 at 7:07 PM, ERIC P. CHARLES <[hidden email]> wrote:

> Below are links to some science videos nifty for two reasons.
>
> 1) They ask and answers a pretty cool question: What happens when you
> hold a slinky out at shoulder height, so it is extended down (the
> bottom still off the ground) and you let go. Think about it for a
> second. How does the top part of the slinky move, how does the bottom
> part move, how does the center of mass move? A good physics thought
> experiment! (If you are having trouble imagining it, here is the question:
> http://www.youtube.com/watch?v=wGIZKETKKdw)
>
> 2) The answer illustrates the weirdness of trying to apply the term
> 'information' to all possible situations. At about 1:30, the physics
> prof offers an explanation for what happens, and (for just a second)
> talks as if one part of the slinky is transmitting 'information' about
> its movement to another part of the slinky, which is bizarre way. The
> slinky itself is moving, it is not transmitting information about the

movement, it IS moving.

> Why would you say that it takes time for 'the information to
> propagate', instead of simply saying that 'it takes time for the
> slinky to move'. Weird, weird, weird.
>
> At any rate, Here is the cool answer:
> http://www.youtube.com/watch?v=eCMmmEEyOO0
> (and it continues here: http://www.youtube.com/wa!
> tch?v=oKb2tCtpvNU&NR=1)
>
> This seemed like the type of thing lots of people on the list would
> get a kick out of... so... hope you do.
>
> Eric
>
> ============================================================
> FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe
> at St. John's College lectures, archives, unsubscribe, maps at
> http://www.friam.org
>

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office: 505.995.0206 mobile: 505.577.5828

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============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives,
unsubscribe, maps at http://www.friam.org

============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org