Interesting slo-mo video of a slinky drop...
 

http://www.youtube.com/watch?v=uiyMuHuCFo4


I wouldn't have expected that behavior.


comment:
His theory is not wrong but there's a more direct explanation. Each ring
gets slightly more tensile force from above than from below, exactly
equal to the weight of that ring. This tensile force only depends on
local extension. When the top is released, tensile force everywhere else
is still the same so the lower parts have no reason to come down. Top
ring comes down, tension immediately below is reduced, next ring starts
moving too. Effect decreases exponentially, so limited to short distance.

Interesting slo-mo video of a slinky drop...
 

In article ,
Richard wrote:

http://www.youtube.com/watch?v=uiyMuHuCFo4


I wouldn't have expected that behavior.


comment:
His theory is not wrong but there's a more direct explanation. Each ring
gets slightly more tensile force from above than from below, exactly
equal to the weight of that ring. This tensile force only depends on
local extension. When the top is released, tensile force everywhere else
is still the same so the lower parts have no reason to come down.¤ Top
ring comes down, tension immediately below is reduced, next ring starts
moving too. Effect decreases exponentially, so limited to short distance.

I don't know if someone hit on it in the comments, which I didn't read,
but the correct explanation rests on the speed of propagation of the
information that the top was released. This information is carried by
mechanical (elastic) waves in the slinky, which travel quite slowly, and
do not travel at anything remotely like the speed of light. You can see
the waves running ahead of the collapse point in the movies.

Joe Gwinn

Interesting slo-mo video of a slinky drop...
 

On 6/24/2012 11:01 AM, Joseph Gwinn wrote:
In articleXNqdnRPjWYlXLXnSnZ2dnUVZ_qSdnZ2d@earthlink .com,
wrote:

http://www.youtube.com/watch?v=uiyMuHuCFo4


I wouldn't have expected that behavior.


comment:
His theory is not wrong but there's a more direct explanation. Each ring
gets slightly more tensile force from above than from below, exactly
equal to the weight of that ring. This tensile force only depends on
local extension. When the top is released, tensile force everywhere else
is still the same so the lower parts have no reason to come down.¤ Top
ring comes down, tension immediately below is reduced, next ring starts
moving too. Effect decreases exponentially, so limited to short distance.

I don't know if someone hit on it in the comments, which I didn't read,
but the correct explanation rests on the speed of propagation of the
information that the top was released. This information is carried by
mechanical (elastic) waves in the slinky, which travel quite slowly, and
do not travel at anything remotely like the speed of light. You can see
the waves running ahead of the collapse point in the movies.

Joe Gwinn


Interesting observation, Joe.
Thanks.

Richard