so this is the modeling that I've been
doing and so this was done with the
purpose of trying to explain the the
data that was extracted from one of the
movies of a real falling slinky
what you see in this one is that the
turns at the top are snapping together
behind a front that propagates down so
the blue section of the top is the part
that has collapsed so initially
nothing's collapsed and then more and
more of the slinky is is collapsed as
that front runs down the slinky and how
close is that to what actually happens
well I think that if you watch the
movies you can see that the turns done
collapse instantly so how did you
improve on that model well I assume that
there's essentially a fixed number of
turns over which that collapse occurs
behind the front those turns they're not
collapsing they're not hammering
together at the top there now you can
gradually relaxing and in fact I've
colored blue the section that is under
collapse or has collapsed and that's
that's far more obvious if you look at
the other video but this to me it looks
much more realistic much more true too
that's why I did it so if someone asks
you why when you let go of this link it
is the bottom not for what do you say
I'd say that there is you know what
you're doing you're changing something
at the top and then there's a finite
time for that information about the
change to get to the bottom of the
slinky I mean that happens even with a
rigid bar with a steel bar just at the
time is very very short
but a lot of people on the internet get
uncomfortable with the term information
I mean what are we saying by information
as a sequence it's a signal so it's
something you know whenever you do
something physically tor to effect a
change causality is you know you do
something and there's a cause and an
effect and that's and between the two
information has to propagate a signal
has to propagate if they're not at the
same location is Italy at the same
location so how long does it take for
the compression wave to get from the top
about a third of a second this new
collapse time is there is there any way
to extend that time because you know if
you decrease the the spring constant
make it a softer spring K yes and then
that takes longer to collapse which is
sort of makes sense the wave propagates
more so you make it more if you increase
the mass of the slinky it gets longer as
well there's more inertia in that
collapse process in a way that yeah you
need kind of a heavy slinky that is very
yeah loose it's odd isn't it like a we
reckon like a lid slinky or if you have
extended systems then to consider the
the motion of the center of mass and
extended system you only need to
consider the the external force that
acts on the center yet on the center of
mass and that's gravity and that starts
into acting you know instantly that this
is released is there to begin with but
its suspended its held out and then once
you take away that suspension that that
center of mass has to start accelerating
downwards instantly so if you watch the
movie you see that the red dot indeed
it's a good test for the modeling the
red dot does start to accelerate and you
didn't build that into the model you
know I only allowed that to after the
fact I calculate the let you know once
you've got the model at each time step I
calculate where that center of mass is
and it you know if it does indeed start
to fall immediately I think we were we
were talking about this earlier and you
actually see the bottom of this things
start to rotate you know now so there's
some kind of torsional mode some
twisting mode a messy signal that gets
down to the bottom of the slinky first
you know rushes ahead but it doesn't
actually relate it doesn't release any
tension clearly because the bottom just
stays
seemingly the only one knows that all
those other turns come down that the
that tension is relaxed I think this
one's finally so in this one you don't
let go of the top of the slinky but you
hold the slinky collapse to the top and
you release the bottom and you hold that
you keep the top fixed and so what it
does is it oscillates back and forth
that's a basic mode in which that whole
thing can oscillate and of course that
mode just depends in a simple way on the
parameters of the slinky so the period
of oscillation that modes a good test
for the parameters that we got
the other modeling out of the falling
the falling slinky this is a very basic
mode that's what I think this is a kind
of breathing mode is this in and out you
know every turn moved in a very simple
way in and out so this breathing logo or
fundamental mode of oscillation wife's